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Summer weed management promotes healthy pastures

By James Locke
Soils and Crops Consultant

Posted Jul. 1, 2015

We usually think of pasture weed management as a springtime activity, and rightly so. If early-season weeds are not controlled, they will compete with desirable forages for space, nutrients, moisture and sunlight. Many of our common pasture weeds are warm-season species that germinate early in the season, and early management can often provide season-long control. If, for some reason, these early season weeds are not managed, the options are limited. Often, they are too large to cost-effectively control with herbicides, and even if we did, they have already caused yield and quality losses. Although mowing pastures is discouraged, in some situations it can be used to remove top growth, allow forage grasses to regrow and improve livestock access to the new growth. Before mowing a pasture, make sure that mowing the weeds is worth more than the value of the forage that will be cut down with them.

While most weeds germinate in the spring, some will germinate later in the growing season and will not be present when springtime herbicides are applied. There are also perennial weeds that are controlled better by late-season herbicide applications. While there are many weeds that can cause summer and late-season problems, the following are a few that I get the most calls about. For other weed species or general management considerations, there are numerous Noble Research Institute and extension publications available.

Woolly croton (doveweed, goatweed) is a warm-season annual with erect growth form and is covered with dense hairs. Its seeds are excellent food for a variety of birds, so if dove or quail are a priority, consider that before controlling woolly croton. It is relatively easy to control with a wide range of herbicides. When it is less than 4 inches tall, 2,4-D does a very good job at a low cost. If allowed to get larger than 4 inches, Weedmaster, GrazonNext and Grazon P+D all do a good job. Woolly croton is a problem because much of it germinates after spring herbicide treatments have been made, and it can have multiple flushes during the season. If this is the primary weed species in a pasture, it may require multiple herbicide applications for season-long control.

woolly croton
A bermudagrass pasture infested with woolly croton

Carolina horsenettle and silverleaf nightshade are both warm-season perennials with sharp spines on their stems and leaves. Reasonably good control can be obtained with GrazonNext, Grazon P+D, Cimarron Max or Weedmaster applied from full bloom through fruiting.

Grassbur, or sandbur, is a warm-season annual or short-lived perennial grass that produces seed capsules armed with sharp thorns. The only herbicides labelled for use during the growing season in pastures are Pastora and Panoramic. Pastora provides good control of grassbur seedlings, but they must be less than or equal to 1.5 inches tall and spray coverage must be adequate. Panoramic provides very good control but has a high risk of serious grass injury. Like woolly croton, grassbur can have multiple flushes from late spring through the fall and may require more than one application. For more information on grassbur control, see the publication Sandbur Control in Bermudagrass Pastures and Hay Fields on our website.

For any of these herbicide options, ensure that the weeds are actively growing and not stressed due to drought, insect pressure, etc., at application. Also, refer to the herbicide label for specific application instructions, rates, precautions, etc. Remember, THE LABEL IS THE LAW.

In addition to herbicides, other practices can reduce summer weed problems. It is important to maintain a solid forage stand that does not allow weeds space to establish. Maintaining proper stubble heights, with appropriate stocking rates and grazing management, can significantly improve the density and competitiveness of forage stands. Also, ensuring adequate fertility and acceptable pH will help make forage grasses more competitive with weeds. By integrating these best management practices with herbicides when needed, one can have clean, productive pastures all season long.

Disclaimer: Reference to specific products is not intended to be an endorsement of these products to the exclusion of others that may have similar uses.

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