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ISSUE 13  JULY 29, 1999

 

THE DARK CLOUD OF WEED RESISTANCE OVERSHADOWS NORTH DAKOTA

    It appears we have progress from a linear increase in ALS resistant kochia to an exponential increase.
ALS resistant kochia has become well entrenched in many areas of ND that in the past have used long
residual sulfonylurea herbicides like Glean, Finesse, Ally, Canvas, and Amber. We have detected
movement into the row crops areas of eastern ND the past few years. Dr. Alan Dexter has perfected
the use of micro-rates in his sugarbeet weed management systems where the use Upbeet, an SU herbicide,
is applied multiple times with other components of the micro-rate treatment. Upbeet is the principle
component to control kochia. In 1999, ALS resistant kochia has become a major problem in the valley
and eastern ND. It is unfortunate that this has happened with cost savings of the micro-rate technology.
Use of other ALS herbicides in small grains, soybeans, corn and other crops has helped feed this
condition. The most significant result of this occurrence is more expense will be used to control the
resistant kochia. It may require tank-mixing with other herbicides that would not have been necessary. It
may require higher rates of other herbicides sacrificing crop tolerance.

    Now for the rest of this discombobulated story....Waterhemp (tall or common) has been documented
near Authur, ND. The weed has survived application of ALS herbicides in soybean. The grower suspects
that the weed came from soybean meal purchased from Minneapolis, feed to hogs, and the manure was
spread on fields which are now infested. This is the first confirmed case of waterhemp in ND. What is
so significant about water hemp? Waterhemp is well entrenched throughout the mid west and has exploded
due to its tolerance (not resistance) of ALS herbicides and due to the extensive use of ALS herbicides in
corn and soybeans. Extensive use of Pursuit and Raptor in soybean has allowed waterhemp to become
well established in many part of the midwest and plains region.

    Waterhemp is dioecious meaning that one plant is male and sheds pollen and the other plant is female
and collect pollen and produces seed. The male plants are colorful with red stems and female plants are
green. Both look similar to pigweed but have lanceolate shaped leaves with shiny foliage and have no hairs
on stems, petioles, or leaves. A concise description of waterhemp, amaranth, and other pigweed species
can be found in "Pigweed Identification", available from the NDSU Distribution Center, 701 231-7882.

    Now for the real bad news. Fields near Erie, ND contains Eastern black nightshade suspected to be
resistant to ALS herbicides, at least Pursuit and Raptor. No infestation of black, Eastern black, or cutleaf
nightshade has not been documented with any resistance to any herbicide to date. If proven true, this
may be the first documented case of resistance in nightshade species. Fields containing suspected resistant
E. black nightshade has a long history of Pursuit use - used at least every other year since registration.
This year, some parts of the field has received 9 fl oz/A of Pursuit Fields were sprayed with Flexstar
which salvaged fields from very heavy nightshade pressure. However, subsequent nightshade flushes
have occurred and some plants not totally killed have resumed growth.

    NDSU Weed Geneticist, Dr. Mike Christoffers will classify gene mutations in several kochia species
collected by Dr. Alan Dexter and classify both the waterhemp and nightshade to document resistant and
determine extent of cross resistant with other ALS herbicides. We are lucky to have such expertise at
NDSU. Dr. Christoffers has become well recognized and regarded nationally and internationally as an
authority on genetics of weed resistance.

    What is the ultimate effect from all this? 1. Dependence on non-ALS chemistry. 2. Use of herbicides
that are very effective on ALS kochia, nightshade, waterhemp, and biennial wormwood. An example is
Authority in soybeans and Spartan in sunflower which provides excellent control of all species mentioned
above. Flexstar in soybean is effective on nightshade all pigweed/amaranth species, including waterhemp.
Flexstar suppresses kochia and is weak on biennial wormwood. 3. Force crop and variety selection
toward transgenic crops Roundup Ready/Liberty Link soybeans, canola, corn, sugarbeet and other crops
as they developed.

 

POISON IVY CONTROL

Poison ivy is abundant. Answers for swift and effective control measures is listed.

Noncropland: Arsenal, Garlon, Oust, and several brands of 2,4-D.
Pastures: Crossbow, Roundup Ultra, Weedmaster.
Lawns: Confront, Trimec brands.

 

WEED CONTROL IN PASTURE, RANGELAND, AND CRP

    Growers continually ask how to control Canada thistle, perennial sowthistle, and other annual
and noxious weed in pasture, rangeland, and CRP WITHOUT killing desirable legumes, such as,
alfalfa, sweet clover. Unfortunately, the most herbicides that are most effective in controlling annual
and perennial broadleaf weeds also kill legumes. These herbicides include Tordon, 2,4-D, Banvel/
Clarity, Curtail, and spot treatment with Roundup. On page 46 of the 1999 ND Weed Control
Guide lists Plateau for annual and perennial weed control in pasture, rangeland, and CRP. Plateau
cannot be used on areas to grazed or cut for hay.
Plateau is in the same chemistry as Pursuit
and Raptor and is safe on legumes, including alfalfa and sweet clover. The Plateau label lists control
of many annual broadleaf and grass weeds at 4 to 6 fl oz/A and many perennial broadleaf weeds at
8 to 12 fl oz/A (See label). The label gives only suppression of Canada thistle a the highest rate. 1998
research by Dr. Rod Lym show May application at 12 fl oz/A + MSO adjuvant gave 80% control
when evaluated July, 70% control in August, and 6% control in October. Fall applications did not
provide greater than 58% control at any evaluations the next year (See 1998 ND Weed Control
Research, pink section, page 13). In other words, spring applications only give 3 months of control
and fall applications do not work. The other factor in the equation is the price of Plateau. Plateau at
12 fl oz/A is $27.00/A and the MSO adjuvant is $2.50/A. The total cost is approximately $30.00/A.
One would seriously have to justify 3 months of weed control for $30.00/A.

PUCKERED SOYBEAN LEAVES

    Each year at this time soybean fields across the state exhibit puckered leaves. What causes this?

    People may speculate that weather conditions, such as, high temperatures, variable humidity influence
puckering. Some think that certain adjuvants and non growth regulating herbicides cause puckering.

    Weed scientists also try to speculate about the cause but what ever is laid to blame for sure one cause
is exposure to growth regulator (GR) herbicides like Banvel, 2,4-D, Stinger, and possibly Starane.
Remember that many premixes contain GR herbicides like Accent Gold, Curtail, Curtail M, Distinct,
Celebrity, Celebrity Plus, Hornet, Marksman, Northstar, Scorpion, and Stinger.

    The following is specific information on GR symptoms on soybean as compared to other leaf crinkling
symptoms. Low doses of GR herbicides will not damage or pucker soybean leaves already exposed.
The malformed leaves emerge after plants were exposed. It is common for affected leaves to emerge
about four leaf nodes after exposure. The leaves that emerge after affected leaves are usually normal.
Deformed leaves can range from puckered and cupped with a yellowish, blunt tip to leaves that are
narrow and strapped with veins that run parallel o the length of the leaf. Typically, puckering and
cupping is associated with Banvel/Clarity and strapping is associated with 2,4-D. But as you would
guess soybean leaves can also be strapped after exposure to Banvel. Type and degree of injury may
depend on dose. Clopyralid, active ingredient in Accent Gold, Curtail, Curtail M, Hornet, Scorpion,
and Stinger may give more strapping than cupping. Fortunately, injury symptoms seldom result in little
to no impact on soybean yield.

    Leaf crinkling frequently occurs after PPO inhibiting herbicides (Blazer, Cobra, Flexstar). Crinkling
occurs to leaves expanding at application. Burning, speckling, and necrotic spots or lesions represent
symptoms of these herbicides. Crinkling may occur because injury may prevent leaf tissue from
expanding. Crinkling may appear on new leaves that expand after application but effects disappear
shortly thereafter.

    How much does it take to cause symptoms? Not much. 1% of 1 pt/A rate of Banvel (5 gallons left
in a 500 gallon tank) causes severe injury. A rate of 0.2% of a 1 pt/A Banvel rate (1 gallon in a 500
gallon tank) causes very noticeable symptoms. Banvel at 0.2% of the labeled rate is equal to a mere
0.03 fl oz/A of Banvel. If 0.03 fl oz/A of Banvel can cause obvious symptoms, that means that it would
take 0.6 fl oz of Banvel to contaminate a 20 acre spray load. It in fact may take less. What would happen
if a quarter ounce of Banvel was added to 400 gallons of spray solution (40 acres worth) and sprayed on
a 90 degree day with 70 to 80% humidity?

    Where does the contamination come from? Drift, and lack of effective tank flush and cleanout. Banvel
and Clarity labels suggest that ammonia cleaning solution should be left in the tank overnight. If the tank
is not cleaned properly subsequent herbicide mixtures may strip the GR herbicides from the matrix of poly
tanks. Oil adjuvants used with many POST herbicides or even the ammonium sulfate used with Roundup
and other POST herbicides can act as tank cleaning agents. Other sources of contamination could be old
jugs used to shuttle herbicides to the sprayer or contaminated transfer hoses or nurse tanks used to fill
sprayers.

    Vapor or particle drift is another source of exposure. Banvel, Banvel SGF and Clarity are formulated
as different salts of dicamba and have different relative volatility potentials. Banvel is an dimethyl amine salt
and has a volatility potential of 10 (10 = high and 0 = low), Banvel SGF is a sodium salt and volatility
potential of 7, and Clarity is a diglycolamine salt and a volatility potential of 2.

 

EFFECT OF BANVEL/CLARITY ON SOYBEAN YIELD

    Behrens and Lueschen (Weed Science 27:486-493) provides a good report on dicamba injury
to soybean from drift. Drift may occur up to 3 days after application in corn. Rainfall after application
greatly reduces vapor movement of dicamba. Low levels of foliar injury did not influence soybean yield
potential. Slight leaf malformations were observed some distance downward of treated corn. More
severe injury ratings of 60 to 70 injury, with terminal bud kill and axillary bud release resulted in short,
bushy beans and delayed maturity. Significant yield loss was not observed unless severe early season
injury or drought stress followed exposure.

    Another study by Weidenhamer and others (Agronomy Journal 81:637-643) found severe
morphological symptoms of growth regulator herbicides as terminal bud kill, stem splitting, swollen
petioles, and curled malformed pods usually represented more than 10% yield reductions. Symptoms
of leaf crinkling and cupping of terminal leaves resulted from herbicides rates much lower than those
required to cause yield reductions.

    Another study conducted in South Dakota by Auch and Arnold (Weed Science 26:471-475) found
interesting results using other experimental parameters. Dicamba was applied at different stages of
development each of three years. Dicamba was applied at 0.03, 0.3, and 1.6 fl oz/A Banvel. Authors
did not record early season injury but mentioned that all rates caused leaf cupping. Significant findings
were that yield response varied from year to year and that exposure of soybeans to dicamba during
bloom stage was more likely to affect yield than exposure during vegetative stages.

    In summary, soybean leaf cupping and crinkling from growth regulator herbicides is a common
occurrence in North Dakota. This is not surprising since North Dakota is at the top or near the top
in small grain production and North Dakota uses more 2,4-D than any state in the nation. Banvel/Clarity
is a well utilized herbicide in our never ending battle against ALS resistant kochia and other problem
broadleaf weeds in grass crops. Research has shown that minor distortions of soybean leaves prior to
bloom usually does not affect soybean yield. However, each situation is different and is impossible to
predict final impact from symptoms that occur early in the season. North Dakota normally may
experience long periods of drought or other stress conditions which may affect the ability of soybean
plants to recover from herbicide exposure. Remember that other factors may induce symptoms typical
of growth regulator herbicides which may complicate diagnosis of the problem. Cupping that frequently
shows up after early-season POST application is merely a cosmetic response with dicamba. More
research could shed more light on the subject.

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

 

GRASS WEED ID NO MYSTERY WITH KEY

    Grass weeds are notoriously more difficult to identify in your fields, especially if no seed head
exists to clarify the culprit weed among several within a similar family. However, six of the most
common grass weeds have been profiled to help you in identifying the yield robbers. So, settle in
for a general description based on the grass weed's leaf blade, leaf sheath, collar, ligule and auricles
to distinguish on grass from another.

    Remember, the leaf sheath is that portion of the leaf that actually encircles the stem. The collar on
the plant is the junction where the leaf blade meets up with the leaf sheath. The ligule is the membrane,
fringe of hairs or combination of those two (if present) where the base of the leaf blade attaches to
the stem and usually can only be seen once you have pulled back the leaf blade and looked at the
inside junction between the leaf and stem. The auricles are the projections on either edge of the collar
which partially encircles the stem. They may be claw-shaped or hook-like, if present.

    Giant Foxtail. The leaf blade is rolled; finely and densely hairy on the upper leaf surface; has scattered
hairs on the lower leaf surface; is distinctly, finely veined. The leaf sheath is hairy and slightly flattened;
ridged at the midvein; open with stiff hairs on the margins. The collar is not divided by a midvein. The
auricles are absent and the ligule is a fringe of hairs that are fused at the base with the longer hairs at
the collar margin.

    Green Foxtail. The leaf blade is smooth and finely veined. The leaf sheath is hairy with overlapping
margins and bristly hairs on the outer margins. The collar is not divided by a midvein. The auricles are
absent. The ligule is a fringe of hairs that are fused at the base with longer hairs at the collar margin.

    Yellow Foxtail. The leaf blade is rolled in a flattened shoot which is smooth except for several
prominent whitish hairs near the base on the upper surface. The leaf sheath is smooth, flattened and
ridged sharply at the midvein. The collar is not divided and is smooth. The auricles are absent. The
ligule does have very short hairs.

    Barnyardgrass. The leaf blade is flattened, smooth and ridged on the underside. The leaf sheath is
smooth and open. The collar is broad but not divided by a midvein and actually has a yellowish-green
collar as well as is smooth. The auricles are absent as is the ligule.

    Quackgrass. The leaf blade is rolled onto the stem and rough on the upper surface and may be
somewhat hairy as you can tell if you rub your finger or thumb along the blade. The leaf sheath is
round and open with overlapping margins that is usually hairy. The collar is distinct as it is divided by a
mid-vein and the auricles are present with claw-like features. The ligule is present but is membranous
and short. The growth habit of this grass may also help in the identification. It is a perennial which
emerges from whitish rhizomes.

    Wild Oats. The leaf blade is rolled onto the stem and is smooth and usually hairless. However, along
the lower edges of the blade, bristly hairs can appear. The leaf sheath is very hairy and is open but has
overlapping margins. The collar is broad and smooth. The auricles are absent. The ligule is membraneous
but prominent even though it is acute.

 

DORMANT WEEDS RESIST HERBICIDE ACTIVITY

    Weed control is limited simply by the huge number of dormant weed seeds that remain in fields. Some
weed seeds can persist for decades in the soil and all are immune to herbicides. In fact, in the tilled layer
of soil (the top six-inch plow layer) weed seeds often reach over 50 million seeds per acre or 10,000 per
square yard. Each year, only 5 to 10% of these weeds germinate and emerge from the ground. The rest
are left dormant, waiting for a future growing seasons or good, opportunist germination conditions.

    Largely, herbicides affect only seeds that germinate. Most dormant seeds remain unharmed. In order
to destroy existing, ungerminated weed seeds, growth must be initiated with costly chemicals (if they can
be and the stimulant can remain active in the soil) or with soil sterilants that also can also kill beneficial
organisms. A more profitable action is to use existing moist conditions through the spring or irrigation
to stimulate germination and then to eliminate the weed seedlings with current herbicides.

    Some nitrogen compounds, growth regulators, anesthetics and a few herbicides can stimulate weed
seed germination. The most successful has been the growth regulator ethylene. Ethylene can even stimulate
the germination of hard to germinate parasitic weeds such as witchweed, which normally requires a
chemical release by the roots of other plants that serve as hosts. Unfortunately, ethylene is costly, difficult
to apply (usually is kept captured in the soil with plastic tarps) and does affect beneficial organisms.

    Stimulants for breaking weed seed dormancy should be able to break the dormancy in seeds that normally
require light to germinate, too, among the many other diverse weed seed characteristics. The stimulant must
be able to penetrate tough weed seed coats and should be volatile enough to distribute the product through
the soil.

    Unfortunately, no miracle product currently exists. However, this year environmental conditions have
helped germinate more weed seedlings than normal due to the very wet spring and continuing, timely rains.
Use this year to provide good weed control on your fields by controlling germinated weeds in order to limit
the number of weeds that contribute to the weed seed bank. Remember now is the time to mow or spray
fence rows (if it has not been done already) and edges of fields in order to limit annual weed seed introduction
into your fields. The fewer weed seeds that remain in the soil will be less time and money spent on control
in future years.

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


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