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ISSUE 13   July 26, 2001



On July 20, 2001, the Environmental Protection Agency (EPA) announced in the Federal Register the availability of a Pesticide Registration (PR) Notice providing voluntary labeling guidelines that will help pesticide applicators prevent the onset of pest resistance. When using the same, or similar, pesticides over time, there is a risk that target pests can become resistant to the pesticide, thereby diminishing its effectiveness. In such an instance, if a grower does not have access to an alternative pesticide, the resistant pests can devastate the grower's crops. By using a variety of pesticides that act differently, the grower can avoid fostering pest resistance, without resorting to increasing application rates and frequency.

Canada and the US developed these guidelines under the North American Free Trade Agreement (NAFTA) to ensure that labels on pesticide products in both countries provide consistent information on preventing insect resistance. This PR Notice recommends that industry voluntarily develop standard language on product labels for providing this information. In addition, the guidelines recommend that industry adopt a standard classification system. The classification system would identify the pesticide's "mode or target site of action," which would be indicated by a number on the front panel of a pesticide product label. Also, product labels should present resistance management statements in the "General" section of "Use Directions," preferably in a box. The Agency will update pesticide classification lists on a regular basis to include new information on products and "mode/target site of actions."

The PR Notice, and its announcement in the Federal Register, are available on EPA's web site at:

http://www.epa.gov/pesticides .

The PR notice itself is not yet posted on the internet, but should appear shortly at:

http://www.epa.gov/PR_Notices/  .



The Environmental Protection Agency has issued rules for regulating genetically engineered crops. The decision came seven years after the rules were first proposed. The rules are supported both by environmental groups and the biotech industry, and EPA has been following them informally. However, there had been some dispute over the regulations among researchers who felt they went too far.

Crops that are developed by conventional methods are exempt from the regulations, although manufacturers must report any adverse effects.

The rules include a provision that says all DNA of the gene-altered crops is safe for food use. Any pesticidal substances in the plant, however, could be subject to restrictions.

Industry officials say that the DNA exemption could make it more difficult for the government to demand recalls of food made with StarLink corn, a genetically engineered corn that was discovered in the food supply last fall although it had not been approved for human consumption.

The Grocery Manufacturers of America said it didn't expect the EPA rules to have any effect on company recall policies.

StarLink corn has been withdrawn from the market, but EPA is deciding whether to renew the licenses of several other varieties, all of which are approved for food use. EPA said it would take public comment on several other exemptions proposed in 1994 but dropped from the rules that were issued recently. One would exempt crops that are altered in ways that only affect the plants, such as producing a waxy coating.



The U.S. Environmental Protection Agency has granted a specific exemption for Poast®, enabling North Dakota safflower growers to use the herbicide to control wild oats in no-till and reduced tillage fields. Heavier than average rainfall in the past few years has resulting in increased weed competition, especially wild oats. Weeds poses a major problem for safflower growers, especially those who use no-till or reduced tillage practices, due to poor safflower competition with weeds.

The exemption allows ground or aerial application of a maximum of 1.5 pints of Poast® per acre.

Applicators must follow all instructions, precautions and warnings on the product label and have a copy of the exemption label in their possession during application. The exemption expires July 31.



Questions have been asked by people observing Canada thistle that are yellow at the top. The rest of the plant looks healthy, just the top 6 inches or so are yellow to almost white. What could be causing this and will the thistle die?

Yellowing on the upper part of Canada thistle plants is due to a natural biological agent (Psuedomonas) found in nature. It only yellows upper plant material, may temporarily stunt shoots but WILL NOT kill shoots. University of MN has done considerable work to isolate the agent and find a way to formulate and market the agent with only limited success. There is not a marketed product on the market yet.

To my knowledge there is nothing anyone can do increase infection and improve control except maybe go to church, pay a healthy tithe and ask for help from above.



NOTE: Even though these results were found many states away from ND, Marestail or horseweed is a common no-till weed in ND and if resistance can happen once somewhere -IT CAN HAPPEN HERE!. Also, the amount of glyphosate used in our chem-fallow, preplant, and preharvest selects for resistance.

A report out of Delaware indicates that marestail (horseweed) that is resistant to glyphosate has been confirmed in three separate fields -- and may be present in as many as six fields in Delaware and others in New Jersey and Maryland. Glyphosate is the active ingredient in Roundup and Touchdown herbicides.

The three fields under scrutiny had similar herbicide histories. Roundup was used in combination with other herbicides as a burndown over a number of years. Over the last three years, each field has had a burndown and an over-the-top application of Roundup or Touchdown with no other herbicides in the rotation. One field sprayed with the recommended rate of glyphosate last season had dead marestail right next to marestail that looked like nothing had happened to it.

Scientists from Syngenta, the manufacturer of Touchdown, are collaborating with scientists on additional tests. Seeds from these surviving plants have been grown out in a greenhouse and treated with 10X rates of glyphosate. The second generation appears to have the tolerance as well.

Marestail or horseweed is a very common winter annual weed in no-till corn and soybean fields. It can germinate in the fall and overwinter in a rosette, or germinate in early spring. It will "bolt" and grow vigorously in March-May and flowers in June/July. The weed does not germinate after very early spring, so early control with burndown or early preplant herbicide applications takes care of the problem. In corn even 2,4-D plus atrazine plus crop oil can be very effective. There are other herbicides like 2,4-D, atrazine, Gramoxone and Banvel that are very effective. Early preplant use of 2,4-D added to the glyphosate will also work.

Glyphosate has always been weak on this weed with control typically in the 50 to 80% range with a lot of variability around that number depending on the size of the weed when sprayed. Farmers typically add a little 2,4-D to improve the control and make it a little more reliable. Does that make it a weed shift or resistance? This is one of the gray areas, like waterhemp will be, where the control was "marginally good" on the original population, but there was obviously a fair amount of potential tolerance in the population in the first place. The end result is the same either way.

Richard Zollinger
NDSU Extension Weed Specialist


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