Don't plant weeds with your winter rye: Weed seed contamination can spell disaster

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

As cash crops come out of the ground and you think about planting cover crops like winter rye, be careful to check the seed for weed seed contamination. Weed seeds can be tiny and difficult to see, but surprisingly numerous in cover crops. For example, a sample pulled from a bag of winter rye in Michigan last week had 95 weed seeds per pound (Photo 1). If you planted this rye at 2 bu/A, that would represent over 10,000 weed seeds.

Among the weed species present in this sample were hairy vetch, smartweed (lady’s-thumb) and corn cockle (Photo 2). These and other weeds sometimes found in cover crop seed can cause problems in subsequent vegetable crops. For example, smartweed is a summer annual that can be difficult to manage in many vegetable crops including broccoli and snap beans. The moral of the story is either pay extra for certified seed, or take a close look at your cover crop seed before purchasing to avoid spreading problems across your fields.

The following is an excellent website for identifying weed seeds:

Weed seeds winter rye
Photo 1. Weed seeds found in winter rye
sample (left) (seeds at approximately
actual size on right).

Close up of weed seed
Photo 2. Close-up of weed seeds from rye sample. Corn cockle or
close relative (left) and smartweed or close relative (right).

Dr. Brainard's work is funded in part by MSU's AgBioResearch.

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