Screening for herbicide-resistance has begun at MSU Diagnostic Services

As suspected resistant weeds reach maturity, it is time to submit seeds for screening.

Horseweed/marestail in a soybean field. Photo by Erin Hill, MSU.
Horseweed/marestail in a soybean field. Photo by Erin Hill, MSU.

Autumn is upon us; crops are nearing maturity and so are the weeds that remain in the fields. If you are concerned those weeds may be herbicide-resistant, consider submitting a sample to Michigan State University Diagnostic Services for screening. We have begun receiving samples and our first round of horseweed was already transplanted from the growth chamber to the greenhouse.

Screening consists of growing weeds in the growth chamber and greenhouse from seed and spraying them under controlled conditions with up to six different herbicides at two rates (based on the species and quantity of seedlings). Plants are evaluated for resistance two weeks after spraying and a detailed report on all herbicides tested is provided. The process from start to finish can take two to five months, depending on the measures required to break seed dormancy for that species and the quantity of samples received.

Tips for collecting weedsPrior to collecting and submitting samples, please refer to “Tips for Collecting Weed Seeds: Ensure your resistance sample gets tested." This four-page document from MSU provides details and color photos showing where to find seeds on the plant and what they look like when mature. It also has information regarding packaging your sample, the form that accompanies it and the address for submission. The most common problems with weeds submitted for resistance screening are immature seeds, insufficient quantity and wrong plant/parts submitted.

The Michigan Soybean Promotion Committee is continuing to sponsor screening for Michigan soybean growers for the following weeds: pigweed species (i.e., Palmer amaranth and waterhemp), horseweed, common ragweed, giant ragweed and common lambsquarters. A fee of $90 per sample is charged for weeds collected from Michigan rotations that do not include soybeans. Weeds other than those listed may also be screened in consultation with MSU Diagnostic Services. Submissions will be accepted until Nov. 1, 2017.

MSU Diagnostic Services is a fee-for-service laboratory that assists in determining the cause of a wide variety of plant health and insect pest problems.  

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