North Dakota State University

Good weed control with PPI and PRE herbicides depends on many factors, including rainfall after application, soil moisture, soil temperature, soil type and weed species. For these reasons, PRE herbicides applied to the soil surface sometimes fail to control weeds. Herbicides that are incorporated into the soil surface usually require less rainfall after application for effective weed control than unincorporated herbicides. Small weeds just emerging through a PRE herbicide may be controlled by a rotary hoe or harrow, which may also help activate the herbicide under dry conditions.

Many factors influence the activity and performance of soil- applied herbicides. Factors that should be considered are: rate too low for soil type, high weed pressure, weeds not listed on label, poor control in wheel tracks, cloddy soil, wet soil, amount of previous crop residue, dry weather, poor incorporation, improper setting of incorporation implement, herbicide resistant weeds, incorporation too shallow or deep, incorporation speed too slow, worn sweeps on cultivator, single pass instead of two pass incorporation, and second incorporation deeper than first. Consider these possibilities before poor weed control is attributed only to the herbicide.

Buckle, Eptam, Far-Go, Ro-Neet, Sonalan, and trifluralin require incorporation. Eptam, Far-Go, and Ro-Neet must be incorporated immediately (within minutes) after application. Trifluralin incorporation may be delayed up to 24 hours if applied to a cool, dry soil and if wind velocity is less than 10 mph. Sonalan incorporation may be delayed up to 48 hours. Pendimethalin is labeled only PPI in soybean, dry beans, and pulse crops and PRE, not PPI, on corn. Alachlor, acetochlor, dimethenamid, and metolachlor may be used PRE but PPI improves weed control, particularly on fine textured soils. Incorporation of alachlor, ethofumesate, and metolachlor may be delayed several days. Incorporation of Eradicane and Eptam can be delayed up to 4 hours when applied with liquid fertilizer and the same day when impregnated on dry bulk fertilizer. Ro-Neet can be incorporated up to 4 hours after application and up to 8 hours when impregnated on dry fertilizer.

A second tillage at right angles to the initial incorporation is needed if a disk or field cultivator is used. The second incorporation will incorporate any herbicide remaining on the soil surface and provide more uniform distribution in the soil, thereby improving weed control and reducing crop injury.

Many herbicides are partially adsorbed and inactivated by soil organic matter, so knowledge of the organic matter level will serve as a guide in selecting an effective herbicide and rate of application. Most soil-applied herbicides require higher rates to be effective in high organic matter soils, but crop safety may be marginal on low organic matter soils. Herbicides also are adsorbed to the clay fraction in a soil, thereby reducing weed control. However, organic matter level generally affects herbicide performance more than clay content.

Some herbicides give good weed control only when organic matter levels are low. Lorox has not been effective in the Red River Valley, except on coarse-textured soils with less than 3% organic matter. The lower the organic matter, the more effective they become. The rate of most soil-applied herbicides must be adjusted according to organic matter levels; apply the high labeled rates on high organic matter soils. Many herbicides such as Far-Go, trifluralin and most POST herbicides are affected only slightly by organic matter levels. Organic matter levels should be determined on each field where organic-matter-sensitive herbicides are to be used. Organic matter levels change very slowly, and testing once every 5 years should be adequate.

Acetochlor, Eptam, Far-Go, metolachlor, Ro-Neet, Sonalan, sulfentrazone, and trifluralin may be fall applied. Trifluralin should be fall-applied when soil temperatures are consistently below 50 F. Sonalan can be fall-applied between October 1 and December 31 in sunflower and dry edible bean in reduced till or conservation tillage systems. Sonalan can be incorporated with a V-blade plow or undercutter. Fall treatments of acetochlor, Eptam, Far-Go, metolachlor, and Ro-Neet should be applied after October 15 and until soil freeze-up. Application of herbicides after October 15, when soil temperature has cooled, minimizes herbicide loss by volatilization and microbial and chemical degradation. Acetochlor, metolachlor, EPTC, and sulfentrazone fall-applied may give poor weed control in spring because of insufficient residual activity. Both granular and liquid formulations of herbicides are registered for use in fall. Granular herbicides fall-applied generally give more effective weed control than the liquid formulations, especially under heavy crop residue situations.

Eptam (EPTC) fall-applied at 4 to 5 pt/A or 17 to 22 lb/A 20G or Ro-Neet (cycloate) at 5.3 pt/A give good control of annual grasses and certain broadleaf weeds. Both must be incorporated into the soil immediately after application to prevent loss of herbicide. The liquid and granular formulations of Eptam may be fall-applied for weed control in dry bean, potatoes, sugarbeet, and sunflower. Ro-Neet is registered only on sugarbeet.

Far-Go (triallate) is applied at 2 to 3 pt/A or 10 to 15 lb/A 10G in the fall when temperatures are consistently below 50 F. See tables for specific rates of liquid and granules for each crop. Far-Go performs best when incorporated immediately after application; however, Far-Go granules may be surface applied in the fall and incorporated with normal tillage operations the following spring. Research at NDSU with fall application indicated that, at similar rates, the granular formulation performed more effectively than the liquid formulation but fall surface-applied Far-Go gave less consistent weed control than when fall incorporated.

Trifluralin fall-applied at 1 to 2 pt/A, or 5 to 10 lb/A 10G (depending on crop) controls annual grasses and some small-seeded broadleaf weeds. Trifluralin liquid or 10G formulations may be applied in spring or fall for weed control in soybean, canola, tame mustard, safflower, dry bean, sunflower, flax, wheat, and barley. Sonalan can be fall-applied or spring-applied but the label does not specify the number of incorporations required. However, herbicide must be thoroughly and uniformly mixed in the top 2 to 3 inches of soil. The number of incorporation passes differ depending on formulation. For Treflan HFP and 10G, incorporation must be performed within 24 hours after application. Sonalan HFP and 10G must be incorporated within 48 hours after application. The second incorporation of Treflan HFP and Sonalan HFP can be done anytime after the first, but the second incorporation of Treflan 10G must be done no sooner than 5 days after the first. The second incorporation of Sonalan 10G must be done no sooner than 3 to 5 days after the first. Delay between first and second incorporation of 10G formulation allows the active ingredient to release from granule. The first incorporation is to cover the granule and the second is to thoroughly mix the active ingredient. Pendimethalin at 2.4 to 3.6 pt EC/A fall-applied in sunflower gives good control of annual grasses and some broadleaf weeds except wild mustard. Incorporation may be delayed 7 days. The liquid may be fall-applied for weed control in sunflower.

Weed control from POST herbicides is influenced by rate, weed species, weed size, and climatic conditions. Low labeled rates will be effective under favorable conditions and when weeds are small and actively growing. Use the highest labeled rates under adverse conditions and for well established weeds.

Sunlight inactivates some herbicides by the ultraviolet (UV) spectrum of light. Trifluralin and Eptam degradation is minimal when incorporated soon after application. "Dim" herbicides (Achieve, Poast, and Select) are highly susceptible to UV light and will degrade rapidly if left in nonmetal spray tanks for an extended period of time or if applied during mid-day. To avoid UV breakdown, apply soon after mixing and with an effective oil adjuvant which speeds absorption.

Ideal temperatures for applying most POST herbicides are between 65 and 85 F. Speed of kill may be slow when temperatures remain below 60 F. Some herbicides may injure crops if applied above 85 F or below 40 F. Avoid applying volatile herbicides under conditions where vapors and particle drift may injure susceptible crops, shelterbelts, or farmsteads.

Temperatures following herbicide application influence crop safety and weed control from herbicides. Crops often metabolize herbicides but metabolism slows during cool or cold conditions, which extends the amount of time required to degrade herbicides in plants. Rapid degradation under warm conditions allows crop plants to escape herbicide injury. Herbicides may be sprayed following cold night-time temperatures if day-time temperatures warm to at least 60 degrees.

Some "Fop" ACCase herbicides are more effective during cold/cool temperatures and are much less effective when grass weeds are drought stressed. Other ACCase herbicides, such as Assure II, Poast, and Select control grasses best in warm weather when grasses are actively growing. ALS grass herbicides in wheat generally provide more consistent and greater grass control in warm, dry conditions compared with cool, wet conditions. Cool or cold conditions at or following application of ACCase herbicides and significant rainfall shortly after Achieve application may increase injury to wheat. Wild oat is a cool season grass but green and yellow foxtail are warm season grasses which may stop growing under cold conditions, resulting in poor control. Grass and broadleaf weeds are controlled most effectively when plants are actively growing.

Cold temperatures, including freezing conditions following application of ALS herbicides, Sencor, and bromoxynil may increase crop injury of labeled crops with little effect on weed control. Delay applying fenoxaprop, ALS herbicides, and Sencor until daytime temperatures exceed 60 degrees F and after active plant growth resumes.

Basagran, Cobra, Flexstar, Reflex, Liberty, paraquat, and Ultra Blazer are less likely to cause crop injury when cold temperatures follow application but less weed control may result.

2,4-D, MCPA, dicamba, clopyralid, fluroxypyr, and glyphosate (resistant crops) have adequate crop safety and provide similar weed control across a wide range of temperatures, but weed death is slowed when cold temperatures follow application.

Dew at application may reduce weed control if spray, in combination with dew, runs off the leaf surface. If no spray run-off occurs after application, weed control may be equal or greater than if no dew was present at application. Rainfall shortly after POST herbicide application reduces weed control because herbicide is washed off the leaves before absorption is complete (See rainfast interval chart below).

Minimum Interval Between Application and Rain for Maximum POST Weed Control.

Herbicide	Time Interval	Herbicide	Time Interval
Accent/STRONG>	4-6 hr	Olympus	4 hr
Achieve	1 hr	Option	2 hr
Aim	6-8 hr	Paramount	6 hr
Amber	4 hr	paraquat	0.5 hr
Assert	3 hr	Peak	4 hr
Assure II*	1 hr	Permit*	4 hr
atrazine*	4 hr	Plateau	1 hr
Avenge	6 hr	Poast	1 hr
Axial XL	0.5 hr	Progress*	6 hr
Basagran*	4-8 hr	Puma	1 hr
Betamix/Betanex	6 hr	Pursuit	1 hr
bromoxynil*	1 hr	Rage D-Tech	6-8 hr
bromoxynil + MCPA	1 hr	Raptor	1 hr
Callisto	1 hr	Redeem	2 hr
Celebrity Plus	4 hr	Reflex	1 hr
chlorsulfuron	4 hr	Remedy	6-8 hr
Clarity*	6-8 hr	Rezult	4 hr
ClearMax	1 hr	Rimfire	4 hr
clethodim*	1 hr	rimsufluron	4 hr
clopyralid*	6-8 hr	RT Master II	1-2 hr
clopyralid+2,4-D/MCPA*	6-8 hr	RU Original Max	1-2 hr
Cobra	0.5 hr	RU Private labels*	4-6 hr
Desicate II	5 hr	RU UltraMax II	1-4 hr
dicamba*	6-8 hr	RU WeatherMax	1-4 hr
Discover	0.5 hr	RU PowerMax	1-4 hr
Distinct/Overdrive	4 hr	Select Max	1 hr
diquat	0.5 hr	Silverado	4 hr
Everest	1 hr	Spartan Advance	4-8 hr
Extreme	1 hr	Starane/NXT	1 hr
FirstRate	2 hr	Status	44 hr
Flexstar	1 hr	Steadfast	4 hr
Fusilade DX	1 hr	thifensulfuron	4 hr
Fusion	1 hr	tribenuron	4 hr
glufosinate	4 hr	Tordon 22K	6-8 hr
glyphosate* (Full adj.)	1-4 hr	TD CT/iQ	2 hr
glyphosate* (Part adj.)	4 hr	TD HiTech	22 hr
glyphosate* (No adj.)	4-8 hr	Touchdown Total	1 hr
Goal	1 hr	Ultra Blazer	4 hr
Halex GT	4hr	UpBeet	6 hr
Hornet	2 hr	Weedmaster*	6-8 hr
Huskie	1 hr	WideMatch*	6 hr
Impact	1hr	2,4-D amine*	44-8 hr
Laudis	1 hr	2,4-D ester*	1 hr
Lumax	4 hr
Maverick	4 hr
MCPA amine*	4-6 hr
MCPA ester*	1 hr
Milestone	4hr

GLYPHOSATE

Glyphosate at 0.188 lb ae/A controls foxtails, at 0.28 lb ae/A controls volunteer small grains, at 0.38 lb ae/A controls wild oat less than 4 inches tall, at 0.75 lb ae/A controls spring germinating and over-wintering downy brome, at 0.75 lb ae/A controls quackgrass at least 8 inches tall (3 to 4 leaf stage) and actively growing, and at 0.75 to 1.125 lb ae/A when Canada thistle is actively growing and just before the bud stage. Glyphosate at 1 lb ae/A is required to control fall planted rye or wheat prior to seeding crops in spring. Tillage should not occur until at least 1 day after treating annual weeds and 3 days after treating perennial weeds.

Glyphosate can be applied in the spring before emergence of conventional crops. Potential for crop injury exists when 2,4-D or dicamba mixtures with glyphosate are applied immediately before or after planting due to the PRE soil activity of 2,4-D and dicamba. A rain event after application and before crop emergence increases risk of 2,4-D or dicamba injury to the emerging crop seedlings.

Below is additional information that may help growers increase effectiveness and consistency of weed control with glyphosate.

1. Glyphosate is very water soluble.
High water solubility is why glyphosate absorption through plant cuticles is slow, activity is greater in humid conditions, NIS adjuvants are either recommended with partial or unloaded formulations or are included in loaded formulations, and why oil adjuvants are not recommend because of their antagonistic affect.

2. Glyphosate activity greatly increases under humid conditions.
Inversely, weed control is reduced under low humidity and when weeds are drought stressed./P>

3. Glyphosate is not deactivated by sunlight.
Time of day application studies show that activity of glyphosate is greatest when applied after 10:00 am and before 4:00 pm.

4. Use the lowest water volume (gpa) allowed on the label.
Low spray water volumes produce spray droplets of high glyphosate concentration which results in greater absorption. Low spray volume also reduces the amount of antagonistic salts in water to interact with glyphosate.

5. Dew on plant foliage at application may reduce weed control. Dew on leaves dilutes herbicide concentration in spray droplets and negates the effect of low spray volume at application. For best results, allow at least a 6 hour rainfast period for all glyphosate formulations regardless of label rainfast recommendation.

6. Use drift management techniques. Glyphosate is a non-selective, non-residual, translocated, foliar herbicide. Glyphosate can cause severe injury or death of plants intercepting even a small amount of active ingredient in down-wind spray droplet drift.

7. Glyphosate is not volatile. Glyphosate does not produce fumes or vapor after application. Off-target movement of glyphosate is from droplet or particle drift, not volatility.

8. Always add AMS to glyphosate.
AMS enhances glyphosate absorption and translocation and deactivates antagonistic hard water salts. The ammonium in AMS makes glyphosate-NH4 as water in the spray droplet on the leaf surface evaporates; glyphosate-NH4 is more readily absorbed than other ionic forms of glyphosate. Addition of AMS increases weed control under good and adverse growing conditions and with or without antagonistic salts in water (See Section A6). Allow sufficient time for AMS to dissolve before application.

9. Glyphosate labels suggest AMS at 8.5 to 17 lb/100 gallons water. However, analysis of water across the state has shown that lower rates (4 to 6 lbs/100 gal) of AMS are adequate. Add AMS at a minimum of 1 lb/A if using greater than 12 gpa spray volume or 4 to 6 lb/100 gallons of water. The amount of AMS needed to overcome antagonistic ions can be determined as follows: /P> llbs AMS/100 gal = (0.002 X ppm K) + (0.005 X ppm Na) + (0.009 X ppm Ca) + (0.014 X ppm Mg) + (0.042 X ppm Fe). See A6 for more information.
Some locations, particularly in western ND, have hard water that exceeds 1600 ppm or even 2500 ppm of combined hardness and require AMS at 8.5 to 17 lb/100 gal water. Growers should know their water quality to determine AMS rate.
If using adjuvants called "Water Conditioning Agents", or AMS Replacement adjuvants, use only those containing at least 4 lbs of AMS/100 gallons of water at their recommended rates. Data show generally less control from most adjuvants in these categories as compared to NIS plus AMS.

10. Add NIS of high quality if the glyphosate label allows use. Research has shown greater weed control even when NIS was added to full-load glyphosate formulations. Use reputable adjuvants from major adjuvant manufacturers. Do not believe claims of cutting herbicide rates by 50%.

11. Oil adjuvants antagonize glyphosate. (See #1).
To control volunteer Roundup Ready crops, to delay weed resistance to glyphosate, and to control weeds that have developed tolerance or resistance to glyphosate require other herbicides to be added with glyphosate. Many of these herbicides are oil soluble (POST grass herbicides, HPPD inhibitor herbicides) and are greatly enhanced by oil adjuvants (petroleum and MSO). The oil adjuvants antagonize glyphosate. AMS has been shown to partially overcome oil adjuvant antagonism of glyphosate from MSO. Adjuvants known as High Surfactant Oil Concentrates (See page 133) also enhance oil soluble herbicides without decreasing glyphosate activity. Using higher rates of glyphosate may partially overcome oil adjuvant antagonism but control of some weeds species may not be adequate.

11. Glyphosate applied during cool and cold weather will kill weeds. The end result (weed control) will be the same as from application in warm weather but the end result will take longer. Ideal temperatures for applying most POST herbicides are between 65 and 85 F. Weeds may be killed slower when temperatures remain below 50 F. Cold weather is a stress to plants. AMS and NIS can be used to overcome the reduced control of stressed plants.

12. Weed control is reduced when glyphosate is applied to desiccated plant tissue affected by frost. Below freezing temperature may burn off top growth and desiccate plant tissue. Plant material injured by freezing temperatures will not translocate herbicides. Application to new plant growth is required for optimum herbicide activity.

13. Plants do not metabolize glyphosate.
Herbicide metabolism is the process whereby tolerant plants avoid phytotoxicity. Except for glyphosate, plants metabolize herbicides, but metabolism slows during cool or cold conditions, which extends the amount of time required to degrade herbicides in plants. No plant has been identified that can metabolize glyphosate, including Roundup Ready crops. Therefore, absorbed glyphosate will remain in the plant until warm temperatures cause plants to resume translocation and glyphosate will be moved via the phloem to growing points.

14. Dust inactivates glyphosate.
Glyphosate absorption in plants is slow which partially explains the 6 to 8 hour rainfast period. Slow absorption allows glyphosate on the plant leaf surface to be inactivated by dust present either on the leaf surface or in windy conditions. This applies also to using slough water for spraying. Mud and soil in slough water will inactivate glyphosate. Addition of NIS or AMS will not overcome inactivation from dirt. Glyphosate is strongly and irreversibly absorbed to clay particles and organic matter.

15. Do not use reduced glyphosate rates.
The price of glyphosate has decreased and weed control is relatively inexpensive compared to conventional weed control strategies. Reducing glyphosate rates may encourage the development of resistant weed biotypes. See "Herbicide Resistant Weeds", Paragraph X1 for more information.

16. Do not apply glyphosate brands formulated with surfactant (partial or full adjuvant formulations) to bodies of water because they include adjuvants that are toxic to fish and aquatic life. Only some non-adjuvant loaded formulations, such as Aquamaster, Glypro, and Rodeo, and some 4 lb ae/gal formulations of glyphosate can be applied on water. An approved NIS surfactant at 0.5 to 1% v/v must be added to non-loaded glyphosate formulations for weed control. Refer to the Adjuvant Section, pages 133, for a list of NIS adjuvants registered for use in water.

Registered Glyphosate Products

Trade name	Manufacturer	Active ingredients	lb ae/ gal	lb ai/gal	Adjuvant Load*
Accord	Dow	glyphosate-ipa	4	5.4	None
Aquamaster	Monsanto	glyphosate-ipa	4	5.4	None
Buccaneer	Tenkoz	glyphosate-ipa	3	4	Partial
Buccaneer Plus	Tenkoz	glyphosate-ipa	3	4	Full
Clearout 41 Plus	CPT	glyphosate-ipa	3	4	Full
Cinco	UAP	glyphosate-ipa	4	5	No
Cornerstone	Agriliance	glyphosate-ipa	3	4	Partial
Cornerstone Plus	Agriliance	glyphosate-ipa	3	4	Full
Credit Duo	NuFarm	glyt-ipa & glyt-NH4	3	4	Partial
Credit Duo Extra	NuFarm	glyt-ipa & glyt-NH4	3	4	Full
Credit Systemic	NuFarm	glyphosate-ipa	3	4	Partial
Credit Syst Extra	NuFarm	glyphosate-ipa	3	4	Full
Duramax	Dow	glyphosate-dma	4	5.4	Full
Durango DMA	Dow	glyphosate-dma	4	5.4	Full
Extra Credit 5	NuFarm	glyphosate-ipa	3	4	Full
Gly-Flo	Arysta	glyphosate-ipa	3	4	Partial
Glyfos	Cheminova	glyphosate-ipa	3	4	Partial
Glyfos X-tra	Cheminova	glyphosate-ipa	3	4	Full
Glyphosate 41%	Helm Agro	glyphosate-ipa	3	4	None
Gly Star Original	Albaugh	glyphosate-ipa	3	4	Partial
Gly Star Plus	Albaugh	glyphosate-ipa	3	4	Full
Mad Dog	UAP	glyphosate-ipa	3	4	Partial
Mad Dog Plus	UAP	glyphosate-ipa	3	4	Full
Makaze	UAP	glyphosate-ipa	3	4	Full
Mirage	UAP	glyphosate-ipa	3	4	Partial
Mirage Plus	UAP	glyphosate-ipa	3	4	Partial
Rattler	Helena	glyphosate-ipa	3	4	Partial
Rodeo	Dow	glyphosate-ipa	4	5.4	None
RT Master II	Monsanto	glyphosate-K	4.5	5.5	Full
RT 3	Monsanto	glyphosate-K	4.5	5.5	Full
RU Original Max	Monsanto	glyphosate-K	4.5	5.5	Full
RU PowerMax	Monsanto	glyphosate-K	4.5	5.5	Full
RU/Private labels	Various	glyphosate-ipa	3	4	Partial
RU UltraMax II	Monsanto	glyphosate-K	4.5	5.5	Full
RU WeatherMax	Monsanto	glyphosate-K	4.5	5.5	Full
Strikeout	-	glyphosate-ipa	3	4	Full
Touchdown CT	Syngenta	glyphosate-K	4.17	5.1	Full
Touchdn HiTech	Syngenta	glyphosate-K	5	6.1	None
Touchdown iQ	Syngenta	glyt -(2(NH3)	3	4	Full
Touchdown Total	Syngenta	glyphosate-K	4.17	5.1	Full

*Full = No additional NIS needed.
Partial = Additional NIS needed.
None = Additional NIS at full rate required.

Glyphosate product rates based on formulation, acid equivalent (ae) and active ingredient (ai).
lb ae       lb ai   0.38 ae 0.57 ae 0.75 ae 1.125ae 1.5 ae
                         --------------------- fl oz/A -------------------
3 =          4 =       16        24         32        48          64
4 =          5.4 =    12        18         24        36          48
4.17=      5.1 =    12        18         24        36          48
4.5 =       5.5 =    11        16         22        32          44
5 =          6.1 =    10        15         20        30          40
Pounds ae/gal or ai/gal are found on glyphosate product labels.
Refer to page 4 for an explanation of active ingredient (ai) and acid equivalent (ae).

A5. SPRAY ADJUVANTS
POST herbicide effectiveness depends on spray droplet retention, deposition, and herbicide absorption by weed foliage. Adjuvants and spray water quality (Section A6) influence POST herbicide efficacy. Adjuvants are not needed with PRE herbicides because retention and absorption by foliage does not occur.
Spray adjuvants generally consist of surfactants, oils and fertilizers. The most effective adjuvant will vary with each herbicide, and the need for an adjuvant will vary with environment, weeds present, and herbicide used. Adjuvant use should follow label directions and be used with caution as they may influence crop safety and weed control. An adjuvant may increase weed control from one herbicide but not from another. Comparisons of adjuvants should be made at marginal control levels to determine the effectiveness of adjuvants for specific herbicides, sprays, water types or volume, and weeds. Effective adjuvants will enhance herbicides at reduced rates and provide consistent results under adverse conditions. However, reduced below labeled rates exempt herbicide manufacturers from liability for nonperformance.

Commercial adjuvants differ in effectiveness with herbicides. Data from the table below are from experiments conducted in ND from 1992 through 1995 comparing commercial adjuvants with Roundup (glyphosate with surfactant) or Honcho (glyphosate without surfactant). Data are included only when a differential in control occurred among adjuvant treatments. In some experiments, all treatments gave similar control, probably because of a more humid and favorable environment for glyphosate uptake and translocation. Roundup/Honcho was applied at lower than labeled rates (2.7 to 4 fl oz/A) so that control would not be complete and differences were much greater at some locations than others.
Commercial adjuvant effect on glyphosate phytotoxicity to selected grass and broadleaf plants^a,b,.

1992-1995^a		1993-1995^a
Adjuvants	Grass	Brdlf	Grass	Brdlf	Grass (range)
	------------------- % control -------------------
Surfactants
None	--	--	49	31	11-68
X-77	62	38	66	40	29-82
R-11	72	55	74	51	34-89
Preference	70	40	67	38	31-84
LI-700	55	36	58	42	16-85
Silwet L-77	66	44	56	40	16-73
Spray Bstr S	65	41	64	41	26-76
Activator 90	67	41	64	41	25-85
APSA-80	--	--	74	50	26-90
Surfactant + Fertilizer
Cayuse+R-11	--	--	82	66	66-94
Class Act	--	--	90	75	80-98
Dispatch	--	--	85	69	73-91
Surfate	-	-	89	75	71-97

^aData for 1992-1995 represent 13 values selected for grass and 12 for broadleaf weeds, except Silwet L-77 had one less site than other adjuvants listed.
^b In 1992, the Honcho formulation (without surfactant) was used and all surfactants were applied at 1% v/v. In 1993-1995, Roundup (with surfactant) was applied and all surfactants were applied at 0.5% v/v except Silwet L-77 was applied at 0.25% v/v in 1995 only. Cayuse + R-11 each were applied at 0.5% v/v. Class Act and Dispatch were applied at 2% v/v, and Surfate was applied at 1.5% v/v in 1992 and 1% v/v in 1993-1995.

All adjuvants enhanced glyphosate (Roundup and Honcho), but some were more effective than others. The last four commercial adjuvants listed in the table are believed to contain ammonium sulfate (ingredients are often a trade secret) and were more effective than the surfactants as a group. The adjuvants differed in effectiveness across locations, possibly from variable spray water quality and environmental conditions at treatment. The results are averaged over various locations and may not represent adjuvant effectiveness for all situations. However, adjuvants differ in effectiveness and users should compare several products for their specific conditions or select an effective adjuvant from the list.

Surfactants are used at 0.12 to 0.5% v/v (1 to 4 pt/100 gal of spray solution). Surfactant rate depends on the amount of active ingredient in the surfactant and other factors such as plant species and herbicides. The main function of a surfactant is to increase spray retention, but surfactants also function in herbicide absorption. When a range of surfactant rates is given, the high rate is for use with low rates of the herbicide, drought stress, tolerant weeds, or when the surfactant contains less than 50% active ingredient. Surfactants vary widely in chemical composition and in their effect on spray retention, deposition, and herbicide absorption.

Silicone surfactants reduce spray droplet surface tension, which allow the liquid to run into stomata on leaves ("stomatal flooding"). This entry route into plants is different than adjuvants that aid in absorption through the leaf cuticle. Rapid entry of spray solution into leaf stomata from use of silicone surfactants often does not result in improved weed control. Silicone surfactants are weed and herbicide specific just like other adjuvants.

Oils generally are used at 1% v/v (1 gal/100 gal of spray solution) or at 1 to 2 pt/A depending on herbicide and oil. Oil additives function to increase herbicide absorption and spray retention. Oil adjuvants are petroleum, vegetable, or methylated vegetable or seed oils (MSOs) plus an emulsifier for dispersion in water. The emulsifier, the oil class (petroleum, vegetable, etc.), and the specific type of oil in a class all influence effectiveness of an oil adjuvant. MSOs have been especially effective with most all herbicides but generally are equal to or better than the petroleum oils with most herbicides (except Cobra). Vegetable oils (non MSO type) are usually equal to petroleum oils. Results vary when comparing specific adjuvants, even within a class of adjuvants.

Fertilizers containing ammonium nitrogen have increased the effectiveness of most herbicides formulated as a salt. Fertilizers should be used with herbicides only as indicated on the label or where experience has proven acceptability.
AMS is recommended at 8.5 to 17 lb/100 gal spray volume (1 to 2%) on most glyphosate labels. Enhancement of glyphosate from AMS is most pronounced when spray water contains relatively large quantities of certain ions, such as calcium, sodium, and magnesium. AMS may contain contaminants that may not dissolve and then plug nozzles. Use spray grade AMS to prevent nozzle plugging. Commercial liquid solutions of AMS are available.

AMS at 8.5 lb/100 gal (1%) is adequate to overcome salt antagonism. AMS at 0.5% has adequately overcome antagonism of glyphosate from 300 ppm calcium. Use at least 1 lb/A of AMS when spray volume is less than 12 gpa. Ammonium ions also are involved in herbicide absorption and have enhanced phytotoxicity of many herbicides in absence of antagonistic salts in the spray carrier. Herbicide enhancement by nitrogen compounds appears most pronounced in certain species like velvetleaf or sunflower.

AMS enhances phytotoxicity and overcomes salt antagonism for dicamba, glyphosate, Poast, and 2,4-D amine. Liquid 28% UAN fertilizer is effective in enhancing weed control from many POST herbicides and overcoming sodium but not calcium antagonism of glyphosate. Sodium bicarbonate antagonism of Poast is overcome by 28% UAN, ammonium nitrate, and AMS. AMS or 28% UAN does not preclude the need for a surfactant. Adjuvants vary in enhancement of herbicide action. The precise salt concentration in water that causes a visible loss in weed control is difficult to establish because weed control is influenced by many other factors.

Some water pH modifiers are used to lower (acidify) spray solution pH because many insecticides and some fungicides breakdown under basic conditions (high water pH). Most solutions are not high or low enough in pH for important herbicide breakdown in the spray tank. pH-reducing adjuvants (example: LI-700) are sometimes recommended for use with herbicides because of greater absorption of weak-acid-type herbicides when the spray solution is acidic. However, low pH is not essential to optimize herbicide absorption. Many herbicides are formulated as various salts, which are absorbed as readily as the acid. Salts in the spray water may antagonize these formulated salt herbicides. In theory, acid conditions would convert the herbicide to an acid and overcome salt antagonism. However, herbicides in the acid form are less water soluble than in salt form. A herbicide acid formed with pH modifiers may precipitate and plug nozzles when solubility is exceeded, such as with high herbicide rates in low water volumes. Antagonism of herbicide efficacy by spray solution salts can be overcome without lowering pH by adding AMS or, for some herbicides, 28% liquid nitrogen fertilizer.

Basic pH blend adjuvants are non-oil and are different from additives that lower spray solution pH. They contain nitrogen fertilizer to overcome antagonistic salts; a surfactant to aid in spray retention, spray deposition, and herbicide absorption; and a buffer to increase pH. Basic pH blends adjuvants increase water pH, which increases water solubility of most ALS and HPPD inhibitor herbicides. For example, Accent solubility at water pH 5 is 360 mg/L, at pH 7 is 12,200 mg/L, and pH 8 is 39,200 mg/L. Basic pH blend adjuvants reduce precipitation problems with Betamix/Betanex/Betamix Progress plus UpBeet at low rates by increasing water pH.

Research has shown that basic pH blend adjuvants enhance weed control similar to MSO type adjuvants. They may be used in those situations where oil adjuvants are restricted. For example, dicamba labels restrict oil adjuvants when used alone or in tank-mix with Accent on corn. Basic pH blend adjuvants are less expensive at field use rates than MSO type adjuvants.

Antagonism of glyphosate by calcium in a spray solution was overcome by sulfuric but not nitric acid, indicating that the sulfate ion was important, but not the acid hydrogen ion. The importance of the sulfate ion explains the effectiveness of ammonium sulfate, and not 28% UAN, in overcoming calcium antagonism of glyphosate. Other herbicides that become acid at a higher pH than glyphosate may realistically benefit from a reduced pH as has been shown for Poast. However, Poast does not require a low pH for efficacy. pH of 4 has overcome sodium antagonism of Poast, but nitrogen fertilizer or AMS also will overcome sodium antagonism of Poast without lowering the pH. The ammonium ion provided by these fertilizers is apparently the important ion.

In summary, adjuvants that are designed specifically to reduce pH generally are not required for herbicide efficacy. The type of acid or components of buffering agents and the specific herbicide all need to be considered before using pH-modifying agents.

Choosing adjuvants with herbicides:
Several POST herbicides allow use of nonionic surfactant, petroleum oil additives, methylated seed oil additives, and nitrogen fertilizer. Questions about adjuvant selection are common. MSO additives have often given greater weed control than petroleum oil additives and nonionic surfactants (NIS) but costs are 2 to 3 times more. The added cost of MSO and increased risk of crop injury when used at high temperatures have deterred people from using this class of adjuvants. Using reduced herbicide rates with MSO can enhance weed control while lowering risk of crop injury.

Some herbicide labels restrict use of oil adjuvants and recommend only use of NIS alone or combined with nitrogen based fertilizer solutions. Follow label directions for adjuvant selection. Where labels allow use of oil additives, a petroleum oil based adjuvants referred to as crop oil concentrates (COC), or methylated seed oil (MSO) adjuvants may be used. The term crop oil concentrate is misleading because the oil type in COC is petroleum oil and not a crop vegetable oil.

NDSU research has shown wide difference in adjuvant enhancement of herbicides. However, in many studies, no or small differences occur depending on environmental conditions at application, growing conditions of weeds, rate of herbicide used, and size of weeds. For example, under warm, humid conditions with actively growing weeds, NIS + nitrogen fertilizer may enhance weed control the same as oil additives. Following are conditions where MSO type additives may give greater weed control than other adjuvant types:

1. Low humidity, hot weather, lack of rain, and drought-stressed weeds or weeds not actively growing due to some condition causing stress.

4. Target weeds are somewhat tolerant to the herbicide. For example, control of wild buckwheat, biennial wormwood, common lambsquarters or ragweed with Pursuit or Raptor, or control of yellow foxtail with Accent.

5. When university data supports use. Most herbicides except glyphosate give greater weed control when used with MSO type adjuvants. Use of oil adjuvants with glyphosate should be used only when research or experience shows no reduction in activity.

Adjuvant use in low gallonage spray volumes
Many herbicides may be applied in low spray volumes by aircraft. In certain instances, spray adjuvant rates should be adjusted for low sprayer volumes. For example, oil adjuvants are applied with ALS, ACCase, and HPPD inhibitor herbicides and other POST herbicides at 1% v/v or 1 gal/100 gal water. At 15 to 20 GPA, 1% oil adjuvant would provide adequate adjuvant load. However, in aerial applications at 5 GPA, 1% v/v may not provide enough adjuvant for the herbicide.

Some herbicide labels contain information on adjuvant rates for different spray volumes. For example, Pursuit and Raptor labels require oil adjuvants to be added at 1.25% v/v or 1.25 gal/100 gal water for aerial application (5 GPA). Additional recommendations to assure sufficient adjuvant load would be to determine the adjuvant rate on an area basis. Instead of using oil adjuvants at 1% v/v, apply at 1.5 to 2 pt/A to insure adequate adjuvant load at all spray volumes. Surfactant rates of 0.25 % v/v or 1 qt/100 gal water is sufficient across water volumes.

Basic pH blend adjuvants are recommended at 1% v/v regardless of spray volume. Data indicate basic blend adjuvants at 1% v/v from 5 to 20 GPA will provide necessary adjuvant enhancement for similar weed control.

A6. SPRAY CARRIER WATER QUALITY
Minerals, clay, and organic matter in spray carrier water can reduce the effectiveness of herbicides. Clay inactivates paraquat, diquat, and glyphosate. Organic matter inactivates many herbicides, and minerals can inactivate 2,4-D amine, MCPA amine, Achieve, dicamba, glyphosate, Liberty, and Poast.

Water in many parts of the United States is high in sodium bicarbonate, which reduces the effectiveness of amine phenoxys, ALS, ACCase, dicamba, glyphosate, and Liberty. Water with 1600 ppm sodium bicarbonate occur, but antagonism of above herbicides was noticeable at or above 300 ppm. The antagonism is related to the salt concentration. At low salt levels, loss in weed control may not be noticeable under normal environmental conditions. However, antagonism from low salt levels will cause inadequate weed control when weed control is marginal because of drought or partially susceptible weeds.

High salt levels in spray water can reduce weed control in nearly all situations. Calcium and magnesium are antagonistic. Calcium antagonism may occur at 150 ppm. Sulfate ions in the solution have reduced the antagonism from calcium and magnesium, but the sulfate concentration must be three times the calcium concentration to overcome antagonism. Natural sulfate in water can be disregarded. The amount of AMS needed to overcome antagonistic ions can be determined as follows:

Lbs AMS/100 gal = (0.002 X ppm K) + (0.005 X ppm Na) + (0.009 X ppm Ca) + (0.014 X ppm Mg) + (0.042 X ppm Fe).

Analysis of spray water sources will determine possible effects on herbicide efficacy. Water samples can be tested at the following laboratory: NDSU Soil and Water Environmental Laboratory, 701 231-7864,Waldron 202, NDSU, Fargo, ND 58105-5575. Analysis is approximately $25.00 to $29.00.

The analysis may report salt levels in ppm or grains. To convert from grains to ppm, multiply by 17 (Example: 10 grains calcium X 17 = 170 ppm calcium). AMS at 2% (17 lb/100 gallons spray) will overcome the antagonism from the highest calcium and/or sodium concentrations in North Dakota waters. However, AMS at 4 lb/100 gal is adequate for most North Dakota waters. Iron is also antagonistic to many herbicides but not usually abundant in ND water.

Water often contains a combination of sodium, calcium, and magnesium, and these cations generally are additive in the antagonism of herbicides. Many adjuvants are marketed to modify spray water pH, but low pH is not essential to the action of most herbicides. AMS, granular or liquid, and 28% UAN fertilizer help overcome antagonistic salts in spray carrier water. Generally, 4 gal of 28% UAN/100 gal of spray has been adequate. UAN overcomes mineral antagonism of most herbicides, but not glyphosate. AMS and 28% UAN enhance herbicide control of certain weeds even in water without salts. Nitrogen fertilizer/surfactant blends may enhance weed control of most herbicides formulated as a salt.

A7. USING HERBICIDES AT REDUCED RATES
Ideally, control of target weeds at the lowest herbicide rate provide the greatest return over herbicide and application costs. This "best" herbicide rate will be different for every herbicide-weed-environment-adjuvant combination. Sometimes, the "best" rate will be lower than the lowest rate on the herbicide label. Below are factors considered by companies when they write a label.

Weed Size and Crop Size. Companies make an assumption of weed and crop size at herbicide application. Small weeds are more susceptible to herbicides than large weeds, but small crop plants may also be more susceptible. Reduced herbicide rates may be used if herbicides are applied to weeds smaller than listed on label. The crop will probably be smaller so knowledge of crop safety also is needed.

Environment. Companies write labels that cover most environments in which herbicides are used. Environment has a large influence on efficacy of herbicides. Herbicide rates may be reduced under ideal environmental but special knowledge and experience is needed on the environment-herbicide interaction.

Adjuvants. Most POST herbicides require addition of adjuvants such as surfactants, crop oils, methylated seed oils, or fertilizer. See section on spray adjuvants (A5) for more information. Adjuvant information is fairly general on pesticide labels to address adequate weed control under most situations. Herbicide rates sometimes can be reduced by using adjuvants that are highly effective with a specific herbicide but additional knowledge is needed. The herbicide-adjuvant combination must be safe on the crop as well as provide good weed control.

Weed Species. Labels sometimes list weed species separately on the label with different rates for different weeds. Herbicide rates may be reduced when highly susceptible weed species are present.

Performance Complaints. Using reduced rates may result in poor weed control. User assumes all risk and liability of unacceptable weed control when less than labeled rates are used.

Are Low Rates Legal? A herbicide user can legally choose a rate lower than listed on the herbicide label unless the label specifically prohibits low rates. However, the company has no obligation to support herbicide efficacy when the application rate was less than labeled rates. Herbicide users should not expect a company representative to provide any comfort or assistance if weed control is less than expected from a rate of herbicide that is less than the labeled rate.

A8. SPRAYER CLEANOUT
Crop injury may occur from a contaminated sprayer. The risk of damage is greatest when spraying crops highly susceptible to the previous herbicide, when the previous herbicide is very active in small amounts, or when tanks are not cleaned after using non-selective herbicides (glyphosate and Liberty). Rinsing with water is not adequate to remove all herbicides. Some herbicides have remained tightly adsorbed in sprayers through water rinsing and even through several tank-loads of other herbicides. Then, when a tank-load of mixture including an oil adjuvant, nitrogen solution, or basic pH blend adjuvant was put in the sprayer, the herbicide was desorbed, dispersed into the spray mixture, and damaged susceptible crops. Highly active herbicides that have been difficult to wash from sprayers and have caused crop injury include dicamba and ALS herbicides.

Herbicides difficult to remove from sprayers are thought to attach to abrasions on tank liners or formulation carrier residues remaining from spray mixtures that deposit in a sprayer, including the boom, hoses, and nozzle bodies. The herbicide must be desorbed from the residue or the residue removed in a cleaning process so the herbicide can be removed from the sprayer. Sprayer cleanout procedures are given on many herbicide labels and the procedure on the label should be followed for specific herbicides. The following procedure illustrating a thorough sprayer cleanup procedure is effective for most herbicides:

Step 1. Drain tank and thoroughly rinse interior surfaces of tank with clean water. Spray rinse water through the spray boom. Sufficient rinse water should be used for 5 minutes or more of spraying through the boom.
Step 2. Fill the sprayer tank with clean water and add a cleaning solution (many labels provide recommended cleaning solutions). Fill the boom, hoses, and nozzles and allow the agitator to operate for 15 minutes.
Step 3. Allow the sprayer to sit for 8 hours while full of cleaning solution so the herbicide can be fully desorbed from the residues inside the sprayer.
Step 4. Spray the cleaning solution through the booms.
Step 5. Clean nozzles, screens, and filters. Rinse the sprayer to remove cleaning solution and spray rinsate through the booms.

Common types of cleaning solutions are chlorine bleach, ammonia, and commercially formulated tank cleaners. Chlorine lowers the pH of the solution which speeds the degradation of some herbicides. Ammonia increases the pH of the solution which increases the solubility of some herbicides. Commercially formulated tank cleaners generally raise pH and act as detergents to remove herbicides. Read herbicide label for recommended tank cleaning solutions and procedures.

WARNING: Never mix chlorine bleach and ammonia as a dangerous and irritating gas will be released.

Sprayers should be cleaned as soon as possible after use to prevent the deposit of dried spray residues. A sprayer should not remain empty overnight without cleaning; fill the tank with water to prevent dried spray deposits from forming. A clean sprayer is essential to prevent damage to susceptible crops from herbicide contamination.

SPRAYER CLEANING SOLUTIONS FOR HERBICIDES
Ammonia + water:
2,4-D, Accent, Ally XP, Amber, Amplify, Assure II, Basis, Cimarron/Max, Classic, dicamba, Escort, Exceed, Expert, Finesse, FirstRate, Harmony GT, Glean, Option, Peak, Permit, Python, Resolve, Steadfast, Stinger.

Ammonia + Simple Green at 1:1 ratio + water:
Callisto, Lumax.

Kerosene or diesel fuel followed by ammonia + water:
2,4-D ester

Ammonia or commercial tank cleaner + water:
Action, Basagran, Beacon, Buctril + Atra, bromoxynil, Callisto, Classic, Cobra, Dual/II/Magnum, Extreme, Fusilade DX, Fusion, Gauntlet, Gramoxone, Harness, Harmony Extra XP, Hornet WDG, Lasso, Lightning, Moxy, Moxynil, Northstar, Prowl, Pursuit, Pursuit Plus, Raptor, Reflex, Resource, Select, Surpass, Treflan, trifluralin, and Ultra Blazer.

Water: Command, Extreme, glyphosate, Lightning, Raptor.

Detergent + water: Aim, Atrazine, and Sencor.

Commercial tank cleaner + water:
Flexstar, Liberty, Liberty ATZ, Shotgun, and Touchdown

Detergent or commercial tank cleaner + water:
Celebrity Plus, Clarity, Distinct, Marksman, Poast Plus, Turbo, Ultra Blazer, Yukon.

Ammonia, commercial tank cleaner, or detergent + water:
Poast.

Baking soda (1 to 2 lb/100 gal water): Engame

A9. SPRAY AND VAPOR DRIFT
Refer to NDSU Extension Circular A-657, "Herbicide Spray Drift" and Circular WC-751 "Documentation for Suspected Herbicide Drift Damage" for additional information. Off-target herbicide movement from fields into areas containing crops or other susceptible plant species should be avoided. The risk of injury to non-target plants varies greatly among herbicides. In general, POST herbicides that are highly phytotoxic at low rates (2,4-D, MCPA, dicamba, Tordon, glyphosate, Liberty, paraquat, and all ALS herbicides have the greatest potential for damaging non-target plants. Spray drift and injury to plants are affected by several factors.

Wind velocity and direction: Apply when wind direction is away from susceptible plants, when velocity is 10 mph or less, and in the absence of temperature inversions. Vertically stable air (temperature inversion) occurs when air near the soil surface is cooler or similar in temperature to air above the crop. Normally, air near the soil surface is warmer than air above the crop. Warm air rises and cold air sinks, which causes vertical mixing of air and dissipation of spray droplets. Small spray droplets can be suspended in stable air, move laterally in a light wind, and affect plants more than two miles downwind. Inversions can be identified by fog or dust from a gravel road.

Distance between nozzle and target (boom height): Adjust boom as close to the target as possible while maintaining uniform spray coverage. Choose nozzles with a wide angle as opposed to narrow angle nozzles.

Herbicide formulation: Some herbicides volatilize under warm or hot temperature and cause plant injury from vapors or fume drift. Low volatile esters of 2,4-D or MCPA may produce damaging vapors between 70 to 90 F. Amine formulations are essentially non-volatile even at high temperatures. Temperature on the soil surface often is several degrees warmer than air temperature. Herbicide vapor can drift farther and over a longer time than spray droplets. Wind blowing away from susceptible plants during application will prevent damage from droplet drift but a later wind shift toward the susceptible plants could move damaging vapors to the plants. To minimize the risk of drift injury, dicamba and ester formulations of 2,4-D and MCPA should not be used near susceptible plants.

Spray shields: Small plastic cones that fit around individual nozzles reduce drift by approximately 25 to 50% and spray shields that enclose the entire boom reduce drift by approximately 50 to 85%. Spray shields provide greater drift reduction when winds are low and droplets are relatively large. Therefore, spray shields should not be used as a substitute for other drift control techniques but as a supplement to all other applicable methods of drift reduction.

Drift control: Spray drift can be reduced by increasing droplet size. Droplet size can be increased by reducing spray pressure, increasing nozzle orifice size, using special drift reduction nozzles, including additives that increase spray viscosity, and orienting nozzles rearward on aircraft.

Drift-reducing nozzles: Several sprayer nozzles are designed to reduce spray drift. These nozzles increase spray droplet size and reduce the number of small droplets. These drift-reducing nozzles are flat-fan types and are adapted for conventional sprayer equipment. The two primary types of drift-reducing nozzles are pre-orifice and air-induction (venturi) designs.

Pre-orifice nozzles: The two most common designs are Drift Guard and Turbo TeeJet nozzles from Spraying Systems Co. Pre-orifice nozzles regulate the liquid flow rate prior to the exit orifice and cause a pressure drop within the nozzle so fewer fine spray droplets are produced. Drift Guard nozzles are available in 80�� and 110�� spray angles with a recommended pressure range of 30 to 60 psi. The Turbo TeeJet design combines pre-orifice technology with a turbulence chamber to produce a wide-angle flat-fan spray pattern that greatly reduces the amount of spray in fine droplets. Turbo TeeJet nozzles are available in 11001 to 11008 sizes with a spray pressure range of 15 to 90 psi although pressures below 30 psi are recommended to maximize average droplet size and drift reduction.

Air-induction (venturi) nozzles. These include the AI TeeJet from Spraying Systems Co., the TurboDrop and TurboDrop XL from Greenleaf Technologies Inc., the Lurmark Ultra-Lo-Drift from Precision Fluid Control Products, the Spraymaster Ultra from Delavan Spray Technologies, and the Lechler ID from Hardi. Each nozzle has a distinct design, but the technology is basically the same. Each includes a pre-orifice to regulate the flow rate so a large exit orifice can be used to produce the spray pattern. Additionally, venturi nozzles include an air-induction assembly that incorporates air into the liquid stream, thereby forming air-filled spray droplets. The design allows air-filled droplets to shatter upon impact thus improving spray coverage and retention of large droplets. A spray pressure of 40 psi will maintain a good spray pattern but pressures greater than 60 psi result in the most consistent performance of POST herbicides. The air-induction system operates more efficiently at higher spray pressures and, in contrast to standard flat-fan nozzles, the droplet size spectrum of venturi nozzles is not greatly influenced by this pressure change.

Drift reduction. Research at NDSU has shown the greatest reduction in spray drift with air induction or Turbo TeeJet nozzles operated at low pressure (20 psi). Drift Guard nozzles significantly reduce drift compared with a standard flat-fan nozzle but produce a quantity of fine droplets that result in greater spray drift than air induction or Turbo TeeJet nozzles. The following table compares droplet size data for various sprayer nozzles (Univ. of Tennessee Agric. Experiment Station, Bull. 695).

*VMD = volume median diameter = diameter in which 50% of the spray volume is in droplets smaller than, not an average droplet size.

Percentage of small spray droplets (<191 m) is the best indicator relating to spray drift. Air induction nozzles (TurboDrop) produced the largest spray droplets and the fewest number of fine spray droplets compared with other nozzles. The data in the table also illustrates the importance of using low spray pressures to maximize the drift-reducing potential of Turbo TeeJet nozzles.

Herbicide performance. NDSU research has demonstrated weed control from glyphosate, Raptor, Pursuit, Distinct, Assure II, and Poast to be similar when applied through drift-reducing nozzles or standard flat-fan nozzles. The same results were observed with fast-acting contact herbicides of Gramoxone Extra and Aim. Reflex applied with drift-reducing nozzles was the only herbicide examined in which weed control was slightly less as compared with a standard nozzle. All other herbicides gave similar control regardless of nozzle.

Sufficient spray coverage to maintain effective weed control is a common question of using nozzles that produce large spray droplets. In most situations, coverage is adequate. Total spray coverage will decrease as droplet size increases, but the number of drops delivered to the target weed will generally still be sufficient for excellent weed control with drift-reducing nozzles.

Even at 5 gpa spray volume, nozzles that produce large spray drops up to 500 m in diameter will theoretically produce 46 drops/sq. inch, which should be adequate to cover even small target weeds. Research at NDSU supports this premise as herbicides applied at 2.5 gpa spray volume with drift-reducing nozzles provided weed control similar to herbicides applied with standard flat-fan nozzles.

Large spray droplets may bounce off leaves upon impact, resulting in poor droplet retention. The concern is legitimate when herbicides are appled without adjuvants. Spray adjuvants applied with POST herbicides improve droplet retention and deposition. NDSU research has found that spray retention is similar for drift-reducing nozzles and standard nozzles when herbicides were applied with NIS or MSO type adjuvants.

For maximum drift control without affecting herbicide performance, use air induction type nozzles at more than 60 psi or Turbo TeeJet nozzles at less than 30 psi. Contact herbicides, hard-to-wet weed species, and small target weeds are examples where drift-reducing nozzles may reduce herbicide performance. Weed control with drift-reducing nozzles may be better than with conventional nozzles when environmental conditions favor lateral droplet movement. Remember to always read the label as some herbicide labels place restrictions on the spray application equipment or spray volume/acre that may be used.

A10. FIELD INVESTIGATION OF CROP INJURY:
Keep an open mind and investigate all possible causes and sources of the problem when assessing crop injury. Question all statements from involved persons about the cause and the source of the problem. The truth often is not obvious. Crop injury can have many causes other than herbicides and symptomology does not always provide definitive answers.

NDSU Extension County, Area, or State staff can assist in determining the cause of observed crop injury and provide an opinion on the severity of the injury. Samples may be collected and sent to the Plant Diagnostic Lab (PDL) at NDSU. However, Extension staff are not responsible for conducting an extensive investigation to determine cause of crop injury or economic loss. Extension staff will not act as a mediator in disputes. Independent consultants can be hired for investigations.

North Dakota Law requires that before a person may file a civil action seeking reimbursement for property damage allegedly stemming from the application of a pesticide, the person shall notify, by certified mail, the pesticide applicator of the alleged damage within the earlier of: 28 days from the date the person first knew or should have known of the alleged damage; or before twenty percent of the crop or field allegedly damaged is harvested or destroyed.

Upon notifying the applicator, the person seeking reimbursement for the alleged property damage shall permit the applicator and up to four representatives of the applicator to enter the person's property for the purpose of observing and examining the alleged damage. If the person fails to allow entry, the person is barred from asserting a claim against the applicator. Individuals can contact the ND Dept. of Agriculture at 600 E. Boulevard, Bismarck, ND 58505-20020. (800) 242-7535 or (701) 328-2231.

The Plant Diagnostic Lab at NDSU will analyze samples and evaluate injury symptoms to provide opinions and possible explanations on the causes of the problem. The PDL does not test soil or plant material for herbicide residues. Refer to "Herbicide Carryover" section (paragraph Y23) for list of testing labs. Analysis of plant tissues or soil by a testing laboratory may not provide a definitive answer to the cause of the problem. Each active ingredient must be tested individually, which increases expense. A positive detection can be useful but the detected herbicide may not have caused the symptoms. A negative test does not prove that the herbicide did not cause the problem because the herbicide may cause injury at concentrations less than the detection limit or the herbicide may have been degraded before the samples were taken.

The pattern of crop injury in a field helps identify the source of the injury. A sprayer skip in a field is valuable in diagnosing a herbicide problem, especially if the applicator remembers the time that the skip occurred. Herbicide field history for the past 2 to 5 years should be considered. Uniform damage over the field would suggest herbicide carryover or injury from a direct application rather than drift.

Drift is nearly always worse near the source of the drift with damage becoming less as the distance becomes greater. Lessening of injury with distance may not be evident shortly after the drift has occurred but the differences should become more visible with time since recovery by damaged plants will be more rapid and more complete as distance from the drift source increases. Crop injury that is associated with one or two sprayer tank loads would suggest sprayer contamination or a mistake in mixing where the wrong herbicide or too much of the correct herbicide was put in the sprayer tank. An aerial photograph often is very useful in identifying patterns of crop injury in a field.

The family of the herbicide that caused the injury often can be identified by the injury symptoms and the species that are not injured. Look in the affected field, in surrounding fields and between fields. The approximate date of injury can sometimes be determined by observing or learning the date that the injury first became evident. The size of plants when affected by a growth regulator herbicide can sometimes be determined by the height of the stem where malformed leaves first occur. Plants that are affected as soon as they emerge usually are being damaged by a herbicide in the soil rather than drift. Dates that injury occurred can be related to dates of herbicide application on and around the damaged field.

The direction of the source of herbicide drift can sometimes be determined by finding "drift shadows" by trees, buildings or elevated roads. Anything that intercepts or deflects spray droplets can cause an area of undamaged plants on the downwind side of the object. The shape and direction of the "drift shadow" often will identify the direction of the drift source. The damage from spray drift sometimes moves at an angle across nearby fields with a rather distinct line between damaged and undamaged plants at the edge of the line.

Placing tall stakes at the edge of this line through the damaged field will often form a line that points at the edge of the field that was the source of the spray drift. Spray droplets move with the wind. Spray droplets will only move down wind so the wind direction during application will often indicate which potential drift sources are possible and which are not possible.

Some herbicides like 2,4-D ester, MCPA ester, and dicamba are volatile and a wind shift after application may cause vapor drift in a different direction than the drift of spray droplets. Spray droplets only move in the direction that the wind is moving.
Some sources of unintended herbicide exposure are very difficult to identify. For example, drift or an accidental and unreported spraying of a long residual herbicide on a tolerant crop would have no effect that year but the residual in the soil the next year could damage a susceptible crop. Another example is soil movement due to wind or water erosion, which causes a damaging level of herbicide to move with soil.

An obvious question is whether to destroy or keep the damaged field. A general rule of thumb is that damage from drift is not as bad as the initial appearance would suggest and a decision should not be made within one week of the drift. With growth regulator herbicides, about 10 days is needed before surviving plants will begin to produce new leaves. Evaluation of the level of injury from growth regulator herbicides should not be attempted prior to 10 days after exposure. With ALS-inhibitor herbicides and glyphosate, the less damaged plants begin to visibly recover and separate themselves from plants with more injury about two weeks after exposure. Rapid conclusions can lead to bad decisions with spray drift.

Everyone involved will want to know how much yield loss will be caused by the herbicide damage. Accurate visual estimation of yield loss from a non-lethal exposure to herbicide is not possible. Some means of collecting meaningful yield comparisons is essential in obtaining an accurate estimate of yield loss. When part of a field is injured and part is not injured, yield in the uninjured portion of the field can be compared to yield in the injured portion. Hand harvesting at several places, harvesters with yield monitors or harvesting and weighing yield from strips through the field all could be used. Usually, splitting the field into six or eight strips or pieces is better than comparing one half of the field to the other half of the field.

Obtaining accurate yield loss data is very difficult when the entire field is damaged. Comparisons to nearby fields can be done but variability among fields is great. Use of the average yield of several nearby fields also could be considered.

A11. GROUNDWATER CONTAMINATION:
Groundwater contamination with herbicides is a public concern. Pesticides can contaminate groundwater by movement from small areas contaminated by spills, spray can and tank rinsate, and back-siphoning (point source) or by movement of pesticides used according to their label on relatively large land areas (non-point source). Point source contamination probably accounts for most groundwater contamination problems and can be minimized by using the following precautions:

1. Mix pesticides away from wells and water sources and maintain at least a 150-ft buffer away from water sources.
2. Prevent back-siphoning into the well by using an anti-backflow check valve or maintaining an air gap between the end of the fill hose and the surface water level in the sprayer.
3. Triple rinse or pressure rinse pesticide containers and add rinsate to the sprayer tank. Visually inspect containers.
4. Minimize extra spray solution by mixing only the quantity of spray required. Apply extra spray solution to fallow land or to a labeled crop following label recommendations.
5. Properly seal active and abandoned wells.

Non-point source groundwater contamination can occur over a broad area as the chemical is leached by water through the soil profile. The potential for non-point source pollution of groundwater with a herbicide depends on soil type, irrigation or precipitation, depth to groundwater, herbicide application rate and frequency, and herbicide mobility. Non-point pollution of groundwater can be minimized by using the following practices:

For further information on ways to prevent groundwater contamination with pesticides, refer to NDSU Extension Service publications EB 49, Persistence and Mobility of Pesticides in Soil and Water, and E-979, Managing Pesticides to Prevent Groundwater Contamination.

A12. MIXING INSTRUCTIONS:
Some herbicide labels list a specific mixing sequence. In absense of specific directions, the recommended sequence for adding pesticide formulations to a tank partially filled with water follows the A.P.P.L.E.S. method: Agitate, Powders soluble, Powders dry, Liquid flowables and suspensions, Emulsifiable concentrates and Solutions.

Each ingredient must be uniformly mixed before adding the next component, e.g., a soluble powder must be completely dissolved before adding the next component. Adjuvants are added in the same sequence as pesticides, e.g., ammonium sulfate is a soluble powder, petroleum oil and

MSO (methylted seed oil) are emulsifiable concentrates; and most surfactants are solutions. Within each group, usually add the pesticide before the adjuvant, e.g., a soluble-powder pesticide before ammonium sulfate.

Many pesticide labels include information on approved tank-mixes. The tank-mix must be applied according to label directions. Non-registered tank-mixes may be applied if all pesticides in the mixture are registered by the EPA on the crop being treated. However, the user assumes liability for crop injury, inadequate weed control, and illegal residues for non-labeled tank mixtures.

A13. HERBICIDE + INSECTICIDE COMBINATIONS are convenient for control of both weed and insect pests. Some combinations have increased crop injury compared to either pesticide applied alone. Efficacy data on herbicide-insecticide mixtures are limited because of the number of potential combinations. Non-registered tank-mixtures should be used with caution until experience or research has shown that the combination is effective and safe. The following information is based on label restrictions and/or research indicating crop injury or decreased control.
2,4-D: Wheat injury but not lower wheat yield with 2,4-D amine combined with Lorsban. 2,4-D, dicamba, bromoxynil+MCPA or Curtail mixed with Asana, Cygon, Di-Syston, Warrior, or Lorsban caused no wheat injury in University of Wyoming studies.

Assert: Use caution when tank-mixing organophosphate insecticides for use on barley and sunflower. Assert and Di-Syston caused barley injury in University of Wyoming research.
Dicamba: Oil-based insecticides increase risk of wheat injury.

Basagran: Basagran should not be tank-mixed with Scout or any organophosphate insecticide as crop injury may result.

Betamix/Betanex: Increased sugarbeet injury occurred from tank-mixtures with Lorsban, malathion, or Sevin XLR. Oil-based additives increase risk of sugarbeet injury.

Bromoxynil: Refer to label for directions on the order of adding products to the sprayer tank and for the complete list of insecticides that can be tank-mixed with bromoxynil.

POST Grass Herbicide:
Assure II, clethodim, Fusilade DX, Fusion, Poast:
Reduced grass control may result from tank-mixes of Fusilade DX with Lorsban, malathion, Sevin XLR, or Pydrin, or Poast mixed with Sevin XLR Plus or Pydrin. No decrease in grass control resulted from Poast tank-mixed with Lorsban or malathion.

Glyphosate: No antagonism or injury to resistant crops occurred when applied in combination with Warrior, Asana, Sevin, and Capture insecticides.

Sulfonylurea Herbicides (SU): Severe crop injury may result from tank-mixing SU herbicides with organophosphate insecticides. Most SU labels do not allow addition of Lorsban or malathion. SU herbicides and insecticides should be tank-mixed only when experience or research indicated crop safety.

A14. HERBICIDE + FUNGICIDE COMBINATIONS can provide weed control and maintain crop protection from some diseases. Information on pesticide labels usually gives all possible registered combinations for each crop. The following table gives information on many possible combinations.

Herbicide/Fungicide Combinations For Small Grains.

NDSU studies show Puma or Discover plus Bronate Advanced applied with the strobilurin fungicides of Quadris, Quilt, Headline, and Gem caused severe leaf burn on wheat; new tissue that emerged was unaffected. Bronate, or generic formulations, plus strobiluron fungicides may also cause similar injury.

A15. HERBICIDE + LIQUID-FERTILIZER COMBINATIONS require thorough mixing and continuous agitation to obtain even application. Some herbicide + fertilizer combinations will not form a uniform mixture even with agitation. To test, combine small quantities of components to be mixed in the same proportions used in the sprayer tank. One tsp of liquid herbicide in 1.5 pt of fertilizer is equivalent to 1 qt of herbicide in 35 gal of fertilizer. One tsp of DG granules in 1.5 pt of fertilizer is equivalent to 1 lb of DG in 16 gal of fertilizer. One tsp of WP in 1.5 pt of fertilizer is equivalent to 1 lb of WP powder in 32 gal of fertilizer. WP and DG formulations should be mixed with water to form a slurry before adding to fertilizer. Shake after mixing.

Watch the mixture for several seconds and check again after 30 minutes. If the mixture does not separate, the combination is compatible. If the mixture separates or gets very thick or syrupy, do not use. Mixing ability may be improved by adding a compatibility agent. Batches of fertilizer may differ in mixing properties and should be tested separately.

HERBICIDE + DRY-FERTILIZER COMBINATIONS created by impregnation on dry bulk fertilizer are used. Read the label for use directions. Ammonium sulfate, ammonium phosphate-sulfate, diammonium phosphate, potassium chloride, superphosphate, treble superphosphate, and urea are approved fertilizer materials for impregnation. Impregnated fertilizer should be applied and incorporated according to label instructions. Consult the herbicide label for minimum amount of fertilizer/A and maximum amounts of herbicide per given weight of fertilizer. Apply at least 200 to 400 lb/A of dry bulk fertilizer to maintain uniform herbicide application.

A16. HERBICIDE STORAGE TEMPERATURES:
Herbicides may be exposed to freezing temperatures in storage. The following information gives the minimum storage temperature to avoid risk of reduced herbicide activity.

No storage temperature restriction
Acetochlor, Aim, Axial/XL, Balance Pro, clethodim, dicamba, Discover NG, EPTC, Extreme, glyphosate-K, Impact, metolachlor, Outlook, Touchdown, and most dry formulated herbicides in DF or WDG formulations.

May store below freezing but warm before using
Betamix, Betanex, MCPA amine and ester, Tordon, Weedmaster

Do not store below 40 F
Assert, clopyralid + ,4-D, Flexstar, Extreme, LI-700, Prowl, Pursuit Plus, Sonalan, Spartan 4F, trifluralin.

Do not store below 32 F
Assure II, Basagran, Beyond, bromoxynil + MCPA, ClearMax, clopyralid, Far-Go EC, Fusilade DX, Fusion, Goal, Grazone P+D, Hyvar, Liberty, Lorox DF, Nortron SC, paraquat, Poast, Pramitol, Progress, Prowl H₂O, Puma, Pursuit, Quest, Raptor, Redeem, Reflex, Reglone, Remedy, Thistrol, Ultra Blazer.

Do not store below 20 F
Define, Fusilade DX, Plateau, Ro-Neet, Starane NXT, Weedar 64

Do not store below 10 F
Amitrole T, Arsenal, clopyralid + MCPA, Crossbow, Fusion, glyphosate, Rodeo, Roundup, Starane, WideMatch.

Do not store below 3 F
Atrazine 4L, Low Vol ester, bromoxynil, bromoxynil + atrazine, Discover, Shotgun.

Do not store below -10 F
Callisto, Lumax

Do not store below -30 F
acetochlor

A17. BACKPACK SPRAYER CALIBRATION
No-Math Version:
Step 1. Mark a calibration plot 18.5 foot wide X 18.5 feet long.
Step 2. Spray the plot uniformly with water while recording the number of seconds required to spray the plot.
Step3. Spray into a bucket for the same number of seconds.
Step 4. Measure the collected volume of water in ounces.
Step 5. The number of ounces collected equals the number of gallons per acre the sprayer is delivering.

A18. HAND-HELD SPRAYERS:
Hand-held sprayers are often used for spot treating patches of weeds or for treating small areas such as lawns. Spray coverage should be uniform, leaves of target plants should be wet but the amount of spray solution applied should be limited so that run-off does not occur. Hand-held sprayers should be calibrated by 1) spraying a known area using water, following standard, reproducible procedure, 2) measuring the amount of water applied, and 3) calculating gallons per acre (gpa). For example, 0.75 gallon on 500 sq ft is the same as 65 gallons per acre:
43,560 sq ft per acre / 500 sq ft x 0.75 gallon = 65 gpa.

The desired rate in lb/A or pt/A can be used to calculate the amount of herbicide to add to the spray solution.

If 3 pt/A is desired: 3 pt/A / 65 gpa = 0.046 pt or 0.73 fl oz or 1.5 tbsp/gal of spray solution (16 fl oz = 1 pt, 2 Tbsp = 1 fl oz).

When calibration of a hand-held sprayer is not possible and the herbicide being used is safe to the environment and non-target plants, a volume of 50 to 70 gpa can be assumed. However, the actual volume applied can vary considerably with the type of sprayer, spray pressure, and technique of the applicator, so calibration is strongly encouraged.

Some herbicide labels specify a percent solution for use in hand-held sprayers. The following chart provides mixing instructions to obtain solutions of varying percent concentrations on a volume/volume basis:

2008 North Dakota Weed Control Guide