Rapid Spread of Resistant Weeds
An example of what Smith noted is why marestail has become a major problem in some places. Glasgow said, “It is a winter annual and can get established in the fall. It starts out as a small rosette on the surface of the soil, and you can probably manage it with some herbicides then, but once it gets any size, it becomes a really difficult one to control. And it is also a prolific seed producer with seed that has characteristics to float long distances in the air.”
Researchers point to the major problems and spread of a few herbicide-resistant weeds causing the biggest concern at the moment. In the Midwest, it is Palmer amaranth, waterhemp, common ragweed, giant ragweed, marestail, and in the West, it is kochia.
UNITED EFFORT TO INFORM FARMERS
As noted earlier, relying on individual states to run their own ID program for resistant weeds has not always worked to help warn farmers as the menace of these weeds and others approach, let alone ways to proactively try to stop the forward movement.
Perhaps the most important program to be initiated recently was one that Johnson has established through the United Soybean Board.
“A year and a half ago, the United Soybean Board (USB), where soybean checkoff money goes, had concern about the spread of herbicide-resistant weeds. So, they approached us about doing a project to encompass as many soybean states as we could include for their funding. So, they’ve had funding in place last year and they funded us again this year for Extension services to raise awareness about the prevalence of herbicideresistant weeds and management programs,” Johnson said.
Only a couple states with at least 2 million acres of soybeans are not participating in this project, he noted.
Part of the project in some states is to get farmers to be aware that resistant weeds are spreading into their farming region and they need to take action before it is too late.
Why aren’t there maps with confirmed resistance found in these counties and suspected resistance in these counties by weed and herbicide? As Johnson noted, the challenges are too much to expect every state to search for these situations and have everything verified. It is impossible to make guesses about weeds resistant to various herbicides due to the nature of weeds, the number of herbicides to which weeds could be resistant and the many variables in farming and environment.
Johnson does send graduate students into the fields to collect samples from areas of the state where certain weeds have not been identified, such as Palmer amaranth, and then also to have them take samples of weeds to see if they are resistant to specific herbicides.
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