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Weed control options to consider

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By Rick Greenwell

Dry weather conditions this summer, following another dry season last year, have resulted in grazed pastures with areas that have thin vegetative cover and bare soil. Much of these areas already has evidence of weedy vegetation, such as common ragweed and other summer annuals. As these plants die back naturally, cool-season weeds such as common chickweed, henbit and purple deadnettle will fill in the voids. Other weeds such as buttercup and musk thistle will likely be more prevalent in the coming spring.

One option to tackle weed problems is to apply broadleaf pasture herbicides in mid to late fall or early next spring. However, herbicides alone may not be the best solution to revitalize pastures for the next grazing season.

The first step to determine your weed management options is to do a critical evaluation of pasture fields. Not only do you need to take an inventory of the current weeds present, but also scout the field to look for any developing weed problems in their seedling growth stages. Identify areas of the field with potential problems such as musk or other biennial thistles, poisonous hemlock, buttercup and common chickweed. Also, you should assess the growth of desirable forage grasses and legumes.

Your primary question then becomes – does the existing stand of desirable forages appear adequate and potentially competitive enough against any emerging weed problems? If the forage stand is acceptable and weed pressure is light, the best course of action likely is to do nothing this fall except other routine pasture management practices. However, if you do see developing weed problems then you may want to take action to begin correcting the problem. In some cases, there may be no good solutions that will correct all weed problems you’ve observed. Here are some points to consider as you make those decisions.

After you evaluate the pasture, you must decide whether or not to 1.) drill or overseed more forages into existing pasture to improve the stand of desirable forage grasses or 2.) spray herbicides to control emerging broadleaf weeds. You will not be able to do both at the same time since most pasture herbicides have the potential to injure newly emerging forage grasses or legumes. For pasture herbicides which contain only 2, 4-D, it’s generally recommended to wait four to six weeks after spraying before reseeding forage crops. Other broadleaf herbicides may require waiting six months or more between the application and seeding forage legumes; make sure and check the label of the specific herbicide product you use. As a general rule of thumb, if you decide to spray this fall, you will need to wait until next spring before seeding additional forages. If you reseed first, then you should wait until the new seedlings have well-established root systems before applying herbicides. It’s important to note that anytime you use broadleaf herbicides, you’ll likely kill any clovers or other desirable legumes in the treated areas.

One alternative to consider in some situations is using a total-pasture renovation technique to control or suppress growth of the weedy vegetation followed by interseeding more forage grasses or legumes. This assumes that you don’t need the field for grazing animals until the newly seeded forages become well established. In this approach, a herbicide product containing either paraquat or glyphosate is applied to “burn back” or kill all existing vegetation before reseeding. Since paraquat and glyphosate have no soil-residual activity, desirable forages can be interseeded into the soil immediately after herbicide application.

Yet another course of action is a “wait and see” approach. But, keep in mind that weeds are much easier to control when they are small and immature. Although you have several options to consider for managing weed problems in the fall, few of these options are viable without some badly needed rainfall.

For more information on pasture weed management, contact the Washington County Cooperative Extension Service.