Starting out with a “clean” field

Eliminating perennial weeds before planting is still important in many crops.

The introduction of glyphosate resistant crops and crop resistance to other herbicides has provided a new and welcoming approach to dealing with quackgrass and other perennial weed problems. Many crop fields have never been “cleaner.” However, there are still instances where a non-herbicide resistant crop is planted into ground that was weedy last year. Genetics for herbicide resistance have been slow to appear in short season corn hybrids, and are not likely to appear in a wide variety of specialty, lower acreage crops any time soon.

Less experienced growers and non-commercial people, such as wildlife plots and gardeners, may attempt to till, maybe even rototill, old, weedy fields thoroughly, then plant. Make no mistake, if quackgrass or other aggressive perennial weeds are tilled up while alive and untreated, they will come back with a vengeance. Any crop production on such land will be seriously damaged and the farmer will learn a hard lesson.

There are two general approaches to cleaning up a weedy field for the following year’s planting.

Non-chemical approaches

“Summer fallow” is an old-time, effective – but time and fuel consuming – method. Fallowing keeps an area relatively free of vegetative cover for an extended period and can result in excessive soil erosion on fields not suitable for the practice. Avoid summer fallowing a field where soil erosion is a concern. Use a field cultivator or other implement to disturb weed roots and pull them up to the surface where they can be dried out by air and sun. Across northern Michigan, an implement knows as a “quacker” was really a field cultivator used for this purpose on quackgrass fields. Also, weed seeds will be brought up near the surface where they will germinate and grow. It is essential to re-work the field often enough to prevent the perennial weeds from re-establishing and to kill germinating seeds and bring up another batch. For reducing weed seed-banks, tillage passes should become gradually shallower. Quackgrass should not be allowed to grow more than 3” between passes. If time is not a problem, use of dense cover crops and those with allelopathic, or plant inhibiting, properties, like fall rye, can help smother out problem weeds prior to a fallow period. By alternating cover crops and tillage over one or two seasons, problem weeds can be effectively reduced, maybe eliminated.

Doing a poor job of summer fallowing, like waiting too long between passes, can actually make a weedy field worse by spreading unkilled perennial weeds, like quackgrass, around the field.

Proper use of appropriate herbicides

Judicious use of herbicides is a much easier and more economical approach. For grass sods, glyphosate at 1.5 pounds active ingredient per acre can provide excellent control, or “kill.” Lower rates are often used, depending on individual field conditions. Perennial legumes like alfalfa or clover are tougher to kill with glyphosate than grasses. Including 1 pound active ingredient per acre of 2,4-D ester will improve results on field including both grass and legumes.

Timing of spray is critically important. Every year, people want to know if they can spray an old hay field with glyphosate, work it up and plant a crop. This practice seems OK at first, but by mid-summer that quackgrass seems to resurrect. Planning ahead and spraying in the fall greatly improves the effectiveness of the herbicide. Glyphosate and 2,4-D need to have a nice, sunny day, preferably over 50oF. In northern Michigan, the last day like that might be in early mid-October. The later the better.

However you approach cleaning up your field, be sure to plan ahead, be systematic and thorough. You’ll be glad you did.

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