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ISSUE 10  JULY 8, 1999

CORRECTION NOTICE -

CRISIS EXEMPTION DECLARED FOR CURTAIL M
    ND Dept of Ag has declared a crisis exemption for Curtail M on flax to control Canada thistle and
perennial sowthistle.

    The crisis exemption allows for a single application of Curtail M at a rate of 1.33 to 1.75 pints/A to
flax 2 to 6 inches tall and to thistle 4 to 6 inches tall. The product must be mixed in 10-20 gallons of
water per acre. Flax treated with Curtail M must not be grazed or fed to livestock. Producers cannot
apply the product within 100 feet of any surface water, including wetlands, lakes, reservoirs, or rivers.
Applicators must follow all instructions, warnings and precautions on the product label. The exemption
expires on July 31, 1999.

 

STINGER SECTION 18 AMENDED

    The EPA has amended the ND Section 18 for the use of Stinger to control Canada thistle and perennial
sowthistle in canola as follows:

    A maximum of one application of Stinger will be made by ground or air at a rate of 0.33 to 0.5 pint
per acre in 10 to 20 gallons of water (a minimum of 5 gallons of water by air).

    All applicable directions, restrictions, and precautions on the EPA-registered product label must be
followed.

 

MAVERICK REGISTRATION

    Full federal registration has been announced for use in winter and spring wheat. Maverick has been
tested extensively for "cheatgrass" control. In winter wheat. ND research has tested Maverick for wild
oat and foxtail control with limited success but grass control is enhanced by certain adjuvants. Weed
control and wheat tolerance has been excellent in NDSU testing. May be positioned for fall early POST
timing for consistent cheatgrass control. Has a long soil residue that will restrict planting any other crops
except wheat for 12 months following application. Complete crop rotation restrictions will be available
in federal label.

 

CONTROL MOSS IN STOCK TANKS AND STANDING WATER

    Algae in stock and nurse tanks can be a nuisance for both animals and for chemical application
especially with hard water. Adding copper sulfate to the water will take care of the problem until the tank
is refilled with fresh water. The process must then be repeated. Dissolve 1 ounce of copper sulfate in 1 pint
of water in a glass jar. Add 0.25 pt/1000 gallons of water. An alternative for nurse tanks is to paint the
entire tank black. This eliminates the sunlight requirement which prevents algae growth.

 

1999 CORN HERBICIDE UPDATE

Action 4.75WP (Novartis)

    Mode of action: PPO Inhibitor
    a.i.:
fluthiacet (proposed) 1.14 to 4.28 oz/A
    Crops:
Corn and soybean
    Comments:
Registration expected in 2000. Contact, nonresidual broadleaf herbicide. Corn leaf
burn may occur with some  adjuvants and hot weather. Narrow weed spectrum velvetleaf, pigweed,
lambsquarters, and nightshade.

Aim 40DF (FMC)

    Mode of action: PPO Inhibitor
    a.i.:
carfentrazone
    Crops: Corn and wheat.
    Comments: $4/A at 0.33 oz/A. Contact, nonresidual, broadleaf herbicide. Narrow weed spectrum
velvetleaf, kochia (+ALS resistant), pigweed, and velvetleaf. Always apply with broadleaf herbicides,
such as atrazine in corn or phenoxy herbicides in wheat. Crop leaf burn may occur with oil adjuvants
and hot weather. DO NOT apply to barley.

Celebrity (BASF)

    Mode of action: ALS inhibitor + Plant growth regulator
    a.i.:
Nicosulfuron (Accent 75DF) + dicamba-Na 70WDG
   Crops: Corn
   Comments: Registered in April of 1998. Use rate is 6.67 of DF/A and is equivalent to Accent
at 2/3 oz DF/A + Banvel at 8 fl oz. Includes a dry formulation of dicamba (sodium salt). Label does
not prohibit use of oil adjuvant (MSO).

Celebrity Plus (BASF)

    Mode of action: ALS inhibitor + Plant growth regulator
    a.i.:
Accent (nicosulfuron) + Distinct (dicamba-Na + diflufenzopyr-Na 70WDG)
   Crops: Corn
   Comments: Registration expected in 2000. Objective is to replace the dicamba in Celebrity with
Distinct in Celebrity Plus.


Distinct (BASF) 70WDG

    Mode of action: Plant growth regulator + Auxin transport inhibitor
    a.i.:
dicamba (Banvel/Clarity) + diflufenzopyr (2.5:1 ratio).
   Crops: Corn
   Comments: Diflufenzopyr has a unique mode of action that synergizes auxin type herbicides (2,4-D,
Banvel, Curtail, Starane, Stinger, Tordon). DO NOT APPLY TO SMALL GRAINS or injury will
occur. Diflufenzopyr in combination with dicamba or picloram (Tordon) has given excellent control
of Canada thistle, sowthistle, and leafy spurge control in NDSU field trials.

Liberty 1.67 (AgrEvo)

    Mode of action: Glutamine synthetase inhibitor
    a.i.:
glufosinate
   Crops: Transgenic corn, soybean, canola, and sugarbeet.
   Comments: Contact herbicide with high activity on annual broadleaf weeds but less on grasses,
especially well tillered grasses. 1999 Section 18 registration cleared on Liberty resistant canola.
No technology fee anticipated for LL corn or soybean. AgrEvo recommends a soil applied herbicide
at half-rate followed by Liberty. AMS recommended with all applications.

Liberty ATZ (AgrEvo)

    Mode of action: Glutamine synthetase inhibitor + Ps inhibitor
    a.i.:
glufosinate + atrazine
   Crops: Liberty resistant corn
   Comments: 32 to 40 fl oz/A. 32 fl oz rate = 20 fl oz Liberty and + 0.8 lb atrazine. Add AMS at 3 lb/A

NorthStar (Novartis) - 47.4%DF

    Mode of action: ALS inhibitor + Plant growth regulator
    a.i.:
primisulfuron + dicamba
    Crops: Corn
    Comments: Beacon at 0.5 oz/A + dicamba at 4 fl oz/A. Targeted use area is north of I-80. Not
actively promoted in ND due to carryover concerns from Beacon. Use NIS at 1% v/v.

Spirit (Novartis) - 57%DF - NOT IN ND

    Mode of action: Both ALS
    a.i.:
primisulfuron (Beacon) + prosulfuron (Peak) in 3:1 ratio or 0.575 oz/A:0.25 oz/A)
   Crops: Corn
   Comments: Same ingredients as Exceed except contains a higher ratio of Beacon and less Peak
for use in some northern U.S. geographic locations to reduce risk of carryover. See label.

ZA1296 (Zeneca)

    Mode of action: Carotenoid inhibitor - same as Balance
    a.i.:
mesotrione
   Crops: Corn
   Comments: Registration expected in 2000. Experimental broadleaf herbicide for PRE and POST
application. Symptoms are plant bleaching. Will not be used after Counter in-furrow nor a tankmix
with an OP. An mesotrione/acetochlor tankmix registration expected in 2001.

Richard Zollinger
NDSU Extension Weed Specialist
rzolling@ndsuext.nodak.edu

 

ECONOMIC THRESHOLDS ARE WAY TO PREDICT
WEED INFLUENCE OR NOT?

    One of the reasons economic thresholds on weeds are so difficult to establish is that they change
depending on crop pricing, date of weed and crop emergence, density counts of the crop and weeds,
crop growth, weather, soil and weed species. And, just the thought of leaving weeds in the field is
alien to our current ideas on clean fields.

    After all, the number of seed that an individual weed plant can produce can be high (barnyardgrass,
7,160 per plant; wild buckwheat, 11,900; kochia, 14,600; lambsquarters, 72,450; wild oats, 250;
redroot pigweed, 117,400; common sunflower, 7,200; Canada thistle, 680). Also, some weeds
emerge at different times through the cropping season. Foxtails can emerge both before and after a
crop is planted and up. And, this weed can have an accumulated effect on the weed seed bank. Even
when buried in the soil, one percent of green foxtail seed can still germinate after 38 years.

    Both germination and dormancy act to determine weed seed viability. Factors that may affect this
include: temperature, moisture, oxygen, light (light or dark may affect), presence of an inhibitor, seed
coat impermeability, mechanically resistant seed coat, immature embryo or the need for after-ripening.
These factors may work alone or in a mix for specific weeds. Other conditions can also influence the
germination including: burning (field bindweed can be reduced in viable numbers) or cutting (when cut
in the flower or bud stage, Canada thistle and dandelion usually have no seed that will germinate, but
common sowthistle has shown to still have 100% germination when cut in the flower but no germination
when cut in the bud stage).

    Economic thresholds are very dependent upon a good understanding of the weed species being
considered. All the variations of factors and variables that affect each weed compound the problem
of devising a method to predict the influence of weeds on crop yields. However, multiple-year studies
can result in a range of weed numbers that may be considered an economic threshold.

    Armed with an economic threshold approximation, one can begin scouting and determining the
risk to take in using weed control. Realizing, of course, that weed economic thresholds are variable
upon conditions and pricing. Your risk acceptance, however, is the real key to accepting economic
thresholds. How much weed seed are you willing to bet with on the farm, are your control operations
timely enough to limit your risk, has early growth of weeds already taken its toll on crop moisture
needs even though a herbicide was applied, are your rotations or other management practices
eliminating weed problems or simply adding to the numbers?

    A recent study was published that examined the affect of foxtail in corn (Weed Science, 47:195-200.
1999) using various crop-weed competition models. This study also examined other research through
the years. In Illinois, for instance, studies have shown a 25% crop loss from giant foxtail at 150 plants
per meter row in a three-year study done in the 1960s. In Michigan, 100 giant foxtail per meter of row
resulted in 40% yield loss in corn. However, earlier than that 1997 report, researchers in Wisconsin did
not show a yield loss at 168 giant foxtail plants per meter row in 1994!

    Variation in crop-weed relationships among years and locations is commonly seen because of all
of the variables mentioned earlier that affect weeds and crops. These differences can result from the
variation in relative time of weed and/or crop emergence; responses of weeds and the crop to different
weather conditions among years; shifts in the resources used and those that become limiting (such as
light, water); or, just changes in crop density as well as variation in other cropping practices.

    Does all of this mean economic thresholds on weeds shouldn't be used? Hopefully, not! Even the
recent modeling study infers that better design and conduction of experiments should be done, after
all much is yet to be learned on specific weed species and even this is ever-evolving. So, take the three
to four foxtail plants per meter row determined by the 1999 computer modeling study as a conservative
estimate of their single-year economic threshold for foxtail along with your approximation of the risk
you are willing to take on your farm to determine your economic threshold across this weed species.

 

WATSON, IS IT OR ISN'T IT HERBICIDE?

    Later season cupping or wrinkling of soybean leaves can mean several different things. Depending
on how good a detective you are out in your field, you should be able to identify the various symptoms.
By using the cropping history and recent weather conditions, further narrow down the culprit(s) to the
damage. When leaves are crinkled or disfigured with plants that may or may not be stunted, possible
causes include: viruses (or other diseases), herbicide injury, insect damage, manganese toxicity, boron
toxicity or just weather conditions.

    Like here, the Midwest has had increasing calls on puckering symptoms on soybeans.

    First, disease problems can cause wrinkling and cupping of soybean leaves. You need to carefully
scout and observe any progress or elimination of the problem over a short period of time to determine
if disease is or is not the culprit. Check with others and find out if diseases have been prevalent in the
area and show the symptoms you are seeing.

    Second, check on the cropping history and the spraying that has been done in the area. Look at
information on the soybean field with the problems as well as the surrounding areas. Do you see a pattern
in the damage or any other field observation that might tie the cupping of the soybean leaves to herbicides?
Don't jump to conclusions, check carefully. One of the first herbicides suggested, if it is herbicide damage,
is Banvel or 2,4-D. Use of either Banvel or Clarity nearby and volatilized can cause puckering of new
soybean leaves, especially leaves that have emerged recently. This damage may last for several weeks
and then disappear. Similarly, 2,4-D will show wrinkling or cupping symptoms. Yield in minor damage
cases is usually not compromised, especially if the soybeans are still in the vegetative stage. Another
herbicide, Roundup, can cause leaf cupping on Roundup-Ready soybeans for a short time under the
right weather conditions. Pursuit, Classic and Pinnacle can also give the appearance of wrinkled soybean
leaves, if conditions are right. Again, continue scouting until the symptoms more clearly define the problem
or they clear up.

    Third, insects such as spider mites or leafhoppers can cause soybean leaf disfigurement. Check for the
insects in the vicinity or other damage that indicates insects are promoting the problem.

    Fourth, if you haven't had your soil sampled within the last three years, it might be worth your time to
run an analysis. It could be the cupping-leaf symptom is simply a micronutrient problem such as manganese
toxicity or boron toxicity. While these micronutient problems are usually not found in this area, check back
on the cropping history and determine what was put on the field in the last three years and if any major
land changes were done on the field˙is it reclaimed land from mining or a railroad crossing˙has soil been
brought in˙have other changes occurred?

    Fifth, and certainly not least, simply consider the weather. Has hot, humid conditions occurred for
several days? Has cool conditions existed? Were the affected soybeans planted in a wet spot in the field?

    Also consider a combination of the above problems. Hot, humid weather sure makes it possible to have
more volatilization of herbicides and insect feeding can add to the puckering-leaf problem! Don't jump to
conclusions. Determine the problem, any patterns (or not) in the field, consider the cropping history and
recent nutrient and chemical applications, scout for insects, look at the weather that occurred the last week
or so and narrow down the problems to make your final assessment on the field.

Denise A. McWilliams
Extension Crop Production Specialist
dmcwilli@ndsuext.nodak.edu


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