© 2003 Wendy Dager

When a Horror Movie Becomes Reality
                 in which two men are fighting over a beautiful woman. One man challenges the other to drink from one of two wine glasses. One glass holds a deadly poison. The other does not. They choose. One man keels over dead.

        Turns out both glasses contained the poison, but the man who does not succumb has spent years consuming small quantities of the toxic substance in order to build up a resistance. He survives, and, in the end, sails off into the sunset with the beautiful woman.

        This is a much more romantic story than the similar tale of invasives that no longer die from herbicides that are supposed to keep weeds from taking over forests, flower fields and crops. And, even more significant a difference than the romance is the fact that our hero built up his own tolerance to poison, while resistant weeds become that way thanks to the evolutionary principle of population genetics. In this case, factors affecting their genes cause these weeds to eventually become uncontrollable.

From Ryegrass to Soybeans

        Without sufficient weed control, crop yields can be reduced by 50 percent or more, crop quality can be impaired, and there is an increased likelihood that crops will be attacked by insects or diseases. When weeds don't respond to herbicides, a veritable monster is on the loose. 20 years ago, herbicide-resistant weeds were first noticed in Illinois soybean fields. Today, nine different herbicide-resistant biotypes, including pests such as waterhemp, ragweed, common lambsquarter and common cocklebur, have been identified in the state.

        But superweeds are not limited to Illinois, nor is the problem only in the United States. An international survey of herbicide resistant weeds, funded and supported by the Herbicide Resistance Action Committee (HRAC), the North American Herbicide Resistance Action Committee (NAHRAC), and the Weed Science Society of America (WSSA), lists 261 resistant biotypes, and 156 species (94 dicots and 62 monocots) in over 210,000 fields.

        Some scientists believe that at least part of the problem may have stemmed from the usage of a popular herbicide containing glyphosate as its key ingredient. Dr. Charles Benbrook of the Northwest Science and Environmental Policy Center reported in May 2001 that reliance on glyphosate to kill weeds in genetically engineered soybean fields had unexpectedly led to increased use of herbicides because the weeds had become herbicide resistant. At that time, the herbicide's manufacturer disputed Dr. Benbrook's findings.

         However, as early as 1997, scientists at the Pesticide Research Center at Michigan University had doubts that glyphosate would work, citing reports that a farmer in Australia-which has more resistant weeds than anywhere else in the world-had found an annual ryegrass that was not controlled by glyphosate.

Glyphosate Resistance: Fact or Fallacy?

        Yet, according to Super Weed Myths and Kryptonite Remedies by Dr. Allan S. Felsot, Environmental Toxicologist at Washington State University, only two weed species have developed glyphosate resistance after 25 years of commercial use. (See Agrichemical and Environmental News, Issue No. 176, http://aenews.wsu.edu/Dec00AENews/Dec00AENews.htm or http://www.botanischergarten.ch/debate/FelsotHerbTolGen3Environm.pdf.)

    "Nevertheless," wrote Dr. Felsot, "weed resistance due to widespread cultivation of herbicide-tolerant crops (whether transgenic or not) may develop as a result of direct selection pressure from the herbicide or as a result of gene flow."

   Weeds have been developing resistance to various herbicides for years, said Dr. Felsot. But strategies to manage resistance have been around along time as well. His recommendations to manage weeds follow the same principles as any other integrated pest management (IPM) strategy, including using a combination of weed control techniques, rotating herbicides, and routinely monitoring the results of herbicide applications.

    In the meantime, scientists have discovered a natural, plant-based herbicide, created from catechin, a chemical found in spotted knapweed-an invasive exotic. A Colorado State horticulture biotechnology professor, Jorge Vivanco, identified and isolated catechin and is using the chemical to control other weeds. This is good news for everyone, including S&S Seeds, where we're all for environmentally-safe herbicide alternatives.

Weed Control Wisdom

        Back in 1997, the Leaf-let gave its readers advice on this very subject (see the Best of the Leaf-let, http://www.albrightseed.com/weedcontrol.htm, "Controlling Weeds, Chemical and Nonchemical"). While nonchemical weed control is environmentally ideal, the most important thing to remember when considering treatment is to evaluate a site thoroughly before taking what might be an overzealous approach, such as an enthusiastic tilling of soil-which might turn up large quantities of dormant weed seed.

     In California, where the weather is warmer than much of the rest of the nation, weeds and pathogens in the soil can be killed prior to new planting by solarizing the soil. This is achieved by creating a "greenhouse effect"-covering the intended planting area with clear plastic for 6-8 weeks. This method relies on sunlight to penetrate the plastic sheet, which prevents heat from escaping.

Wildflower Management

    As Leaf-let readers begin planting wildflowers, there must be an understanding of how to introduce wildflowers into a landscape, while assessing a site for weed control. (See the Best of the Leaf-let, Wildflowers! Getting Along With Mother Nature, http://www.albrightseed.com/wildflowers.htm.)

    Knowing specifically which weeds you will need to control will make the choice of eradication methods easier and should be a consideration in wildflower selection.
    For maintenance, herbicides for "broad leaf" plants are generally unsafe for wildflowers. Herbicides labeled for "grass" weeds can be used safely with most wildflowers.

    Should you have any questions about weed control in managing your wildflower plantings this season, give us a call at S&S Seeds, (805) 684-0436, and we'll be glad, as always, to offer our expertise and guidance.

Buy Wildflower Seeds now!

GREENFIX America EarthSaver Straw Wattle Slope Interruption Device A low cost solution to sheet and rill erosion problems. Can replace silt fences or straw bales on steep slopes. Helps establish and store moisture for native vegetation. Plastic netting photodegrades and straw becomes incorporated into soil.         Call S&S Seeds at (805) 684-0436.

Albright Seed is a Division of S&S Seeds.

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