ISSUE 11 July 16, 1998
HERBICIDE MIXING ORDER
The post-emergence herbicide season brings out the multiple product "cake mix" combinations and associated compatibility questions. Product formulations along with additive type, water quality and temperature are factors. General mixing order listed below will help reduce problems when used with required agitation during the process, depending on the products in the tankmix.
1. Fill tank nearly full with water.
2. Add ammonium sulfate or fertilizer additives.
3. Add wettable powders.
4. Add dry flowables DF and flowable liquid residual herbicides.
5. Add emulsifiable concentrates (EC).
6. Add water soluble solutions (such as 2,4-D, Clarity, etc.).
7. Add other liquid solutions (Roundup, Touchdown, etc.).
8. Add surfactant or oil concentrates.
TWISTED WHORLS AND "YELLOW FLAGS"
Twisted or "buggywhipped" corn was common in corn fields. Evidence of some leaf wrapping, crinkled leaf tissue and yellowish chlorotic leaves emerging from the whorl is still apparent. While the initial symptom could be compared to herbicide effects; the problem this year is primarily associated with a sudden return to rapid growing conditions. New leaves deep in the whorl began growing rapidly and were unable to push through the older tissue that was not expanding. The upper part of the plant may bend; however, most plants finally unroll with minimal final effects.
Adapted from "Field Facts", SDSU Extension Service Newsletter, Volume 12, No 7, July 2.
AERIAL APPLICATION OF CLARITY
The ND Department of Agriculture has issued a SLN (State Local Needs) label allowing Clarity to be applied by aerial application in small grains, pasture, rangeland, and fallow at 1 to 5 gallons dilution rate.
SOME THOUGHTS ON FIELD PROBLEM INVESTIGATION RELATED TO HERBICIDES
Keep an open mind and investigate all possible causes and sources of the observed problem when making a field visit. Do not accept, without question, statements of involved persons about the cause and the source of the problem. The truth often is not obvious. Remember that crop injury can have many causes other than herbicides and symptomology does not always provide definitive answers. Do not make concluding statements until your investigation is complete. Only make statements that can be supported by facts. Assume that any statements you make while investigating a problem may be repeated to you while you are under oath.
The Plant Diagnostic Laboratory at North Dakota State University will accept samples and provide an opinion on the cause of the problem. However, the Plant Diagnostic Laboratory does not presently analyze plant tissues or soil for herbicide residues. Soil and plant residue testing is being discussed and may be available in the future. Until soil and plant analysis are available opinions on the cause of plant injury will be based on injury symptoms.
Be aware that analysis of plant tissues or soil may not provide a definitive answer to the cause of the problem. Each herbicide must be tested individually so testing can be very expensive if numerous herbicides are the possible cause of the problem. A positive detection of a herbicide can be useful but the detected herbicide may not have caused the symptoms. A negative test for a herbicide does not prove that the herbicide did not cause the problem since the herbicide may cause injury at levels 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 will help identify the source of the injury. A sprayer skip in a field will be valuable in diagnosing a herbicide problem especially if the applicator remembers the reason and the time that the skip occurred. The history of herbicide use on the field for the past 2 to 5 years should be examined. A 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. The 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 the recovery of the damaged plants will be more rapid and more complete as the 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 spray 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 which 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 Banvel 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 the soil.
The person who has the damaged field will want to know if the field should be destroyed or kept. A general rule of thumb is that damage from drift is not as bad as it looks 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 side 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.
Extension Sugarbeet Weed Specialist
RESTRICTIONS FOR LATE HERBICIDE USE IN DRY BEAN AND FIELD PEA
Timely postemergence herbicide application in dry bean or field pea may have been delayed due to adverse weather or other reasons. If herbicides still need to be applied to the rapidly- growing legumes, keep in mind the following application limitations based on crop stage.
Pursuit - before flowering.
Assure II - 30 days before harvest.
Basagran - 30 days before harvest.
Poast/Ultima 160 - 30 days before harvest.
Chiptox - maximum of 6-inch vines.
Rhomene - maximum of 6-inch vines.
MCPA amine - maximum of 7-inch vines.
Pursuit - before flowering.
Thistrol - prior to pea flowering.
Assure II - 60 days before harvest
Sencor - 50 days before harvest.
Basagran - 30 days before harvest.
Poast/Ultima 160 - 30 days before harvest.
ASSERT IN SUNFLOWER
North Dakota has a supplemental label for use of Assert for wild mustard control in sunflower. Use 0.6 to 0.8 pt/A or 4.5 to 6 ounces/A Assert WGD when the majority of wild mustard plants are in the rosette stage and prior to bloom. Be sure to read and follow the label information. Consider the following points when using Assert for weed control in sunflower:
* Apply Assert to 2- to 8-leaf sunflower that also are less than 15-inches in height. Do not apply to sunflower under drought or heat stress. A rule-of- thumb used is if air temperature plus relative humidity total about 150, do not apply Assert. Weather conditions, sunflower variety, growth stage, spray volume, spray additives, and type of application have all been contributing factors to injury that occasionally has been severe. Sunflower damage from misapplication may range from plant stunting to head deformation.
* Do not tank mix any insecticides or herbicides with Assert.
* After Assert application, wait 4 to 5 days before between-row cultivation.
Area Extension Specialist