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ISSUE 11  July 13, 2000



    In my last article, I discussed how several POST herbicides are equally or more effective when applied in low spray volumes (2.5 to 5 gpa) with the proper adjuvant rate. This article will provide a little more background on applying herbicides in low volumes and address some of the concerns regarding low volume application.

    One question that is often raised is will the spray coverage be sufficient enough to maintain effective weed control. In most situations, it will. It is correct to assume the total spray coverage will decrease as spray volume decreases since less water is being delivered to the plant. However, applying more spray to each plant does not necessarily result in a greater amount of herbicide remaining on each plant. Our research has, in fact, showed just the opposite. When comparing herbicide retention at 5, 10, and 20 gpa (volume changed by speed so the droplet size spectrum was similar among spray volumes), less herbicide remained on the plant at 20 gpa compared to 5 or 10 gpa. Herbicide concentration increases proportionately as spray volume decreases, so that an equal amount of herbicide is delivered to each plant, regardless of spray volume. In other words, a greater proportion of the herbicide delivered to the plant is retained when spray volume is 5 or 10 gpa rather than 20 gpa.
This may be due in part to spray runoff at 20 gpa. While spray runoff may be desirable for canopy penetration, it is generally not a desirable aspect for most weed control situations.

    Will herbicides perform well in low spray volume with dew present on weeds is another common concern. First of all, as the spray combines with the dew, spray runoff will more likely occur at high spray volume compared to low spray volume, thereby reducing the amount of herbicide remaining on the plant. Also, important is the increased herbicide and/or adjuvant concentration as volume decreases. The spray mixture is diluted when it combines with the dew, but remains more concentrated with low spray volume compared to high spray volume. Herbicide absorption increases as concentration
increases for several herbicides including glyphosate (Roundup) and sethoxydim (Poast). Likewise, the adjuvant concentration would be greater for low volume application compared to high volume, which would be beneficial for both herbicide retention and absorption.

    The increased herbicide and particularly adjuvant concentration with low spray volumes is also important when controlling weeds under stress. Herbicide absorption can be a limiting factor for controlling stressed weeds and the greater the adjuvant concentration in the spray mixture, the greater the herbicide absorption. However, a stressed crop will metabolize the herbicide more slowly, so increasing herbicide absorption may result in greater crop injury.

    Certainly, low spray volumes are not the answer for every herbicide or every spray application situation. For example, NDSU research has shown reduced weed control as spray volume decreased for some contact herbicides such as Flexstar/Reflex. But as previously mentioned, applying herbicides in low spray volume may actually result in better herbicide performance compared to high spray volume under certain adverse environmental conditions.

Dr. Brad Ramsdale
NDSU Weed Science, Application Technology



    The EPA will not allow the importation of Achieve 80DG herbicide from Canada into the state of North Dakota. A technicality in federal law currently forbids importation of a Canadian-labeled product, even if the product is registered in the U.S.

    FIFRA (Federal Insecticide, Fungicide and Rodenticide Act) does not permit the actions recently recommended by the State of North Dakota Department of Agriculture (NDDA) that individuals re-label the Canadian Achieve 80DG and import it into North Dakota. The EPA ruled that FIFRA does not give EPA the power to regulate pesticide prices.

    NDAA may attempt to develop an import process allowable under EPA rules, seek a change in federal pesticide laws, or take legal action to force harmonization of pesticide prices between the U.S. and Canada.

    Producers and applicators with questions about Achieve 80DG may call NDDA Plant Services at (800) 242-7535 or (701) 328-2231. The EPA response can be found on NDDA's website at  www.agdepartment.com.



    Kochia can influence normal and development of spring wheat by releasing allelopathic chemicals These finding come from a report of an investigation carried out by two students from Northern Toole County Sunburst High School, Montana. They studied the effects of certain plants like kochia, wild oat, and wild buckwheat to see if they produce either root exudates (allelochemicals) or some other mechanism associated with water soluble chemicals that inhibit or adversely affect the
germination and growth of spring wheat.

    Bottom line: Wild oat and wild buckwheat showed no effect on emergence, rate of growth, average vegetative dry weight or final height and had no effect on germination of spring wheat. In contrast, kochia had a significant negative effect on the emergence and average vegetative dry weight of spring wheat grown in pots. The average vegetative dry weight of spring wheat plants was significantly reduced by root exudates of kochia grown in sterilized soil but not in unsterilized soil.

    Allelopathy refers to the exchange of any chemicals known as secondary metabolites of plant, fungal, or microbial origin that influence the growth and development of other plants or microbes. Allelopathic potential has been suggested for around 90 species of weeds and some allelochemicals have been elucidated. Allelochemicals can be released by a plant through volatilization, leaching or exudation.

    For additional information on this subject refer to http://scarab.msu.montana.edu/agnotes/index.htm.

Richard Zollinger
NDSU Extension Weed Specialist

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