Plant & Pest Diagnostics

History & map of herbicide-resistant weed species in MI

• Learn what weeds have been confirmed as herbicide-resistant in specific counties
• Visit the map at this link to learn more
• Updated: April 2019

Submitting your weed seed sample for testing

• Tips for collecting weed seeds: Ensure your resistance sample gets tested
• Submission form – Screening for herbicide resistance at MSU Plant & Pest Diagnostics
• Testing includes multiple sites of action, based on seed quantity and quality – $90.00
• MI Soybean growers qualify for free testing of the following species courtesy of the
  Michigan Soybean Promotion Committee:
  • Palmer amaranth
  • Waterhemp
  • Horseweed/marestail
  • Common lambsquarters
  • Common ragweed
  • Giant ragweed
• MI Vegetable growers qualify for free testing in 2020 thanks to a grant from the MI Vegetable Council in collaboration with Drs. Sushila Chaudhari and Erin Hill. This testing is available for any weed species suspected of being herbicide resistant in a vegetable rotation.
• Testing of other species in other cropping systems may be possible in consultation with the Weed Diagnostician, Erin Hill (hiller12@msu.edu)

Weed seed is required to conduct a whole plant bioassay in the greenhouse to screen for herbicide resistance. Mature, high-quality seed or seedheads should be collected from suspicious plants in the late summer or fall; ideally pooled samples with seed/seedheads from 5 or more plants will ensure adequate seed quantity. For species-specific seed collection and submittal information please refer to the top link above. Screens will be designed by herbicide site of action (e.g. EPSP synthase inhibitor, ALS inhibitors, Photosynthesis inhibitors, etc.) and are generally available 2-3 months after submission to allow for seed cleaning, dormancy breaking measures, greenhouse growth, herbicide application, and evaluation.

From the MSU Field Crops Weed Science Group in the Department of Plant, Soil and Microbial Sciences:

• Weed Control Guide for Field Crops (E-434)
• Factsheet series
  • Identification
    • Keys to distinguishing Palmer amaranth from other species
  • Management of resistant weeds
    • Keys to management of multiple-resistant Palmer amaranth and waterhemp in soybean, corn and alfalfa
    • Keys to management of herbicide-resistant horseweed (marestail) in no-till soybean

From the MSU Vegetable and Fruit Weed Science Group in the Department of Horticulture:

• Weed Control Guide for Vegetable Crops (E-433)