Cool Season Crops Help Manage Resistant Weeds

By Scout Nelson

South Dakota farmers continue to face challenges from herbicide resistant weeds, including Palmer amaranth and waterhemp. These broadleaf weeds grow well in annual crop systems and can develop resistance when the same herbicide methods are used often.

The information is presented by Clarence Winter, SDSU Extension Agronomy Field Specialist, along with Eric Jones and Sunish Sehgal. Their work shows how adding cool season crops to crop rotations can help farmers create stronger competition against weeds while supporting other farm goals.

How Cool Season Crops Help

Palmer amaranth and waterhemp grow quickly when temperatures become warm. Their seeds can emerge over a long period during the growing season. This allows the weeds to appear at different times, including after the main crop has already started growing.

Warm season crops such as corn, soybeans, and sunflowers develop during the same part of the year when these weeds become active. This can give Palmer amaranth and waterhemp opportunities to grow between crop rows and under a developing crop canopy.

Cool season crops offer a different growth pattern. Crops such as wheat, rye, oats, and canola establish earlier in spring or begin growing during the previous fall. By the time warm season weeds reach their main emergence period, these crops can already provide strong ground cover.

Crop Rotation Can Support Weed Control

Adding a cool season crop is not always simple for farmers. Some producers may have limited experience with small grains. Others may not have the equipment, markets, or storage needed for these crops.

Using different crops as part of a planned rotation can help farmers manage resistant weeds over time. It is one part of a broader weed management system that can include crop competition, herbicides, tillage when appropriate, and practices that reduce weed seed production.

Dual Purpose Winter Wheat Offers Flexibility

Dual purpose winter wheat can provide another option for farmers who want to add a cool season crop. SD Sundog is an awnless hard red winter wheat variety developed by South Dakota State University for both forage and grain production.

The variety offers good forage yield potential along with high grain yield potential. It also provides good test weight, strong grain protein content, and good end use quality. Its early maturity gives farmers more flexibility when making decisions about forage, grain, and other crops.

Farmers can harvest the crop for forage and still have the opportunity to produce grain, depending on growing conditions and management decisions. An early forage harvest may also create time to establish another crop later in the season.

In some areas, this may allow a double crop. A later planted warm season crop, such as sunflower, can be an option when soil moisture, herbicide restrictions, and the remaining growing season allow it.

Weed Management Benefits

The value of a dual purpose crop is not limited to how farmers harvest it. Winter wheat begins growing well before the main emergence period of Palmer amaranth and waterhemp. This gives the crop an opportunity to capture sunlight, water, nutrients, and growing space before these weeds become most active.

Strong crop growth can reduce the resources available to emerging weeds. It can also help reduce opportunities for weeds to mature and produce new seeds. Lower weed seed production can help limit the number of weed seeds added to the soil for future growing seasons.

For farms with livestock or forage needs, a dual purpose winter wheat variety can serve more than one purpose. It can provide forage while also fitting into a crop rotation designed to improve weed management.

A Broader Weed Management Strategy

Cool season crops do not replace every other weed control practice. Instead, they can become part of an integrated system that uses several methods to manage resistant weeds.

Farmers can consider crop rotation, competitive crops, forage systems, timely weed control, and practices that prevent weeds from producing seeds. Choosing crops with different growth patterns can make the overall cropping system less favorable for weeds.

For producers dealing with Palmer amaranth and waterhemp, adding cool season crops provides another practical option. With proper planning, crops such as winter wheat can support weed management while also meeting grain, forage, livestock, and crop rotation goals.

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