Now is an excellent time to make choices about managing weeds in pastures. Before applying herbicides for chemical control you first need to answer the question, “Why do I have weeds in my pasture?” If a management issue such as overstocking, spot grazing, low grass vigor or something else is causing the increase in weed numbers, then weeds are symptoms, not the real root of the problem. Managing for improved grass vigor through better soil fertility and grazing at the proper time and intensity can greatly reduce most weed issues, particularly annual weeds.
On the other hand, there may be instances when grazing management and soil fertility alone cannot address weed issues. In these situations, coupling chemical control with proper grazing and soil fertility can lead to a long term solution.
Annual broadleaves are easiest and most economically controlled when they are small (2 to 4 inches tall.) In addition, if weeds are killed when they are small they don’t compete as much with desirable forages resulting in a much greater yield response when weeds are controlled early in the growing season as compared to later. The proper timing for that annual weed size is usually somewhere between mid-April and the first of May in Southeast Kansas. Perennials are best controlled when they are flowering or have completed flowering and actively growing, usually sometime in June depending on the weed. Obviously weed growth and the weather don’t always abide by the calendar, so for best results always follow the rates and weed sizes listed on the label.
There are several different chemical options available. The best option for you will depend on price, effectiveness, and the weed type and size you are going after. A few of the chemical options are:
- 2,4-D works well on small annuals and at a higher rate satisfactorily on perennials.
- A rate of 3/4 lb. of active ingredient per acre will give good control on small annuals.
- A rate of 1 to 1 1/4 lbs. will be needed for larger annuals or perennial plants.
For a broader spectrum of weed control and in some cases residual control, 2,4-D in combination with aminopyralid, dicamba or picloram may be an effective option. Be sure to read the label for the proper mixing procedures and a list of those weeds controlled. Metsulfuron is also another option, which provides residual control.
Metsulfuron can also suppress fescue production and seedheads. There are several herbicides in which Metsulfuron is the primary ingredient. An excellent K - State publication with specific recommendations for different weeds and forage types is available at: https://www.bookstore.ksre.ksu.edu/pubs/chemweedguide.pdf for 2018 KSU Chemical Weed Control.