Resistant, yes or no? Submit your weed seeds for screening at MSU Diagnostic Services.

Collect seeds of suspected herbicide-resistant weeds and submit for screening to Michigan State University Diagnostic Services.

Powell amaranth plants
Powell amaranth plants in screening for herbicide resistance. Photo by Erin Hill, MSU.

Fall is just around the corner and the growing season is coming to an end, but the time to have weeds screened for herbicide resistance is just beginning. If you are concerned the weeds that escaped control this season are herbicide-resistant, consider submitting a sample to Michigan State University Diagnostic Services for screening. Samples of mature weed seeds have started to trickle in and the process of greenhouse screening will begin shortly.

We are fortunate to have the continued sponsorship of the Michigan Soybean Promotion Committee to support screenings for Michigan soybean growers for the following weeds: pigweed species (e.g., 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, 2018.

To collect and submit seed, consult our fact sheet, “Tips for Collecting Weed Seeds: Ensure your resistance sample gets tested.” This document illustrates where to find the seeds on the plants and what the seeds look like. It is critical to check for mature seeds prior to submitting a sample to avoid requests for repeat collection and submission. It is also important to submit a sufficient quantity of seed, with five or more plants being recommended per sample.

Screening consists of growing weeds from seeds in the growth chamber and greenhouse and spraying seedlings 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 as little as two months to as long as five months, depending on the dormancy breaking requirements of the species and the quantity of samples received.

Michigan State University 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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