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Forages and Pastures

Weeds can reduce the quantity and the longevity of desirable forage plants in pastures and hayfields. These unwanted plants are often more aggressive than existing or desired forage species and compete for light, water, and nutrients. Weeds can also diminish the quality and palatability of the forage available for livestock grazing, and certain weed species are potentially poisonous to grazing animals. Therefore, it may be desirable to initiate weed management strategies that reduce the impact of weeds on forage production. However, not all weedy plants are detrimental to pastures or hayfields. In fact, some weedy plants provide nutritional value to grazing animals; therefore, an effective weed control program is essential to establishing and maintaining highly productive pastures and animal performance.

“An ounce of prevention is worth a pound of cure.” This traditional advice is still relevant today. Cattle and calves are big business in Tennessee, and high-quality forages are essential inputs. Ninety-five percent of our pasture and hay is composed of cool-season grasses (85 percent tall fescue, 10 percent orchardgrass). Approximately 25 percent of this acreage has been renovated with Ladino and/ or red clover. Forages, particularly cool-season grass pastures and hay fields, are the backbone of the beef industry. There are several management practices which will help prevent weeds from taking over pastures and hayfields.

Regardless of whether it is a fescue and legume pasture, a bermudagrass or an alfalfa hay field, most annual and perennial broadleaf weeds reduce forage yield, palatability and quality. This is particularly true if heavy populations of broadleaf weeds are not controlled on a timely basis and are allowed to reach maturity. The ideal approach is to incorporate practices that are more adaptable to the growth of the desirable forage species and less favorable for unwanted plants.

  • Selecting well-adapted grass and/or legume species that will grow and establish rapidly. This will minimize the length of time for weeds to invade easily.
  • Putting down lime and fertilize according to soil test recommendations. Proper pH and nutrient status will help insure that the forage will grow rapidly and be more competitive with weeds.
  • Managing grazing properly. Overgrazing is a common cause of weed problems. Heavy grazing pressure may favor weed growth over grass; whereas under grazing will allow new weed seedlings to emerge and invade the pasture area.
  • Mowing at proper timing and stage of maturity for forages.
  • Renovating and rotating pastures when needed.
  • Allowing new forage seedings to become well established before permitting cattle to graze on the pasture.
  • Using herbicides can be another useful tool for weed management in pastures and hayfields.

A program that integrates several different control strategies is generally more successful than relying on only one method. Weeds present at the time of herbicide application may be controlled, but if the forage stand is not vigorous and actively growing, new weed seedlings will soon emerge and occupy the bare areas that remain. Thus, without proper use of mechanical control methods and good cultural practices, herbicide use will not be beneficial.

  • Identify the type of weeds that need to be controlled. Use the UT Weed Science Weed Identification List or the UT 2018 Weed Control Manual for Tennessee (pdf) to aid in correctly identifying the weed species.
  • Different weeds have different life cycles. Common weeds that occur in Tennessee forage crops can be divided into four categories based on their life cycle. Knowledge of weed life cycles is particularly important in the timing of herbicide applications. The four categories of weeds based on life cycle are:
    • Summer annuals — Plants that germinate from seed in the spring, flower and produce seed in mid to late summer, and die in the fall. Examples include large crabgrass, barnyardgrass, common cocklebur, spiny amaranth, spurge, ragweed and bitter sneezeweed.
    • Winter annuals — Plants that germinate from seed mostly in late summer through winter, flower and produce seed in late winter to spring, and die in late spring to early summer. Examples include annual ryegrass, little barley, hairy buttercup, chickweed, henbit, purple deadnettle and Carolina geranium.
    • Biennials — Plants that complete their life cycle over two growing seasons. They germinate and produce a vegetative rosette the first year. The second year the plants bolt, flower, produce seed and die. Examples include musk thistle, bull thistle, wild carrot and common burdock.
    • Perennials — Plants that produce a vegetative structure (taproot, tuber, bulb, rhizome, etc.), which allows them to live for more than two years. Most perennials also reproduce from seed. Examples include johnsongrass, buckhorn plantain, horsenettle, tall ironweed, goldenrod, brambles and black/honeylocust.
  • Select the proper herbicide product for the control of weeds present. Always consult the label before using a herbicide product! For more information concerning herbicide products, refer to the publication Weed Management in Pastures and Hay Crops (PB1801) (Table 4, “Herbicides for Grass Pastures and Hay Fields,” pages 7-8).
  • Proper timing of a herbicide application should be based on stage of weed growth; potential risk to nearby sensitive crops; and environmental conditions, such as air temperatures, humidity, and wind. Refer to the “Spray Today?” section in this website.
  • Annual broadleaf weeds are easier to control when herbicides are applied to plants that are small and actively growing. Perennial broadleaf weeds tend to be most susceptible when plants have reached the early bloom to bloom stage of growth.

Spray drift can result in reduced weed control at the target field, damage to adjacent crops and desirable vegetation, environmental pollution, expensive fines and/or lawsuits, and bad publicity for our industry.

  • Movement of small amounts of commonly used pasture herbicides (2,4-D, Banvel, Crossbow, ForeFront R&P, Grazon P+D, Milestone, etc.) away from treated fields can cause serious damage to sensitive crops such as cotton, tobacco, tomatoes and other vegetables, vineyards, and ornamental nurseries.
  • There are two types of drift, physical and vapor, and both can occur.
    • Physical drift is the movement of liquid spray droplets (usually the finer or smaller droplets) away from the target. Factors that increase the likelihood of drift include wind, high temperatures and a sprayer setup that produces high pressures and low application volume (a large number of small spray droplets).
    • Vapor drift is most influenced by air temperature. Some chemicals volatilize (change from a liquid to a gas or vapor) readily at warm (85 F) temperatures. While less obvious than physical drift at the time of application, vapor drift can be just as damaging.
  • Small amounts of herbicides such as 2,4-D in sprayers can create serious problems if the same sprayer is used to apply pesticides to crops such as tobacco, tomatoes, peppers, melons and other vegetables. It is strongly advisable to have a dedicated sprayer for pasture herbicides and not use this sprayer on sensitive crops.
  • The following are suggestions to reduce the likelihood of drift from herbicides:
    • Know adjoining farms and other properties well. Most producers are familiar with their neighbors and know if they grow sensitive crops. Check on when your neighbor, for example, plans to set tobacco or plant cotton, and which fields he or she plans to use this year. Information of this nature will allow you to plan accordingly for individual fields. Also, be familiar with locations of outdoor tobacco float beds, greenhouses, vineyards and container nursery operations.
    • Set up your sprayer to produce large droplets. High-volume (20 to 30 gallons per acre),low-pressure (20 psi or less) applications will reduce the number of “fines” or small spray droplets. One of the problems with low pressure in the past has been that flat-fan nozzles would not develop patterns adequately at low pressure. Manufacturers have made great advances during the last several years with the development of low-pressure, extended-range flat-fan tips and air-induction spray tips. If your farm supply store does not stock these tips, ask the dealer to order them for you.
    • Try to spray at a time of year when sensitive crops are not growing. This is often difficult to accomplish because the optimum time for weed control may occur when a sensitive crop is in the field. However, some weeds, such as musk thistle, may be treated after mid-October with 2,4-D. This would be a good approach for a field across the fence from your neighbor’s tomatoes or tobacco, in that 17 you could treat at a time of year when the crop has already been harvested. This should also be considered in areas where cole crops (broccoli, cauliflower, cabbage) are grown, as most producers in Tennessee grow spring crops rather than fall crops, of these sensitive vegetables.
    • Avoid spraying on windy days. Although this is common sense, it is one of the most effective ways to reduce physical drift. In general, calm conditions are more likely to be encountered either early or late in the day. Actually, a slight breeze blowing away from the sensitive field is one of the better situations for managing drift.
    • Reduce the risk of vapor drift, use the amine formulation of 2,4-D rather than the low-volatile ester formulation. This is particularly important with late spring to summer applications, when warm (85 F) temperatures are likely to be encountered at or shortly after spraying. The amine formulation is much less volatile than the low-volatile ester formulation. This is very important to remember, in that vapor drift will be worse under warm conditions, and that it can occur even a few days after application. Other temperature-sensitive herbicides include Banvel, Crossbow and Weedmaster.
    • Last but not least, read the herbicide label for drift reduction measures or restricted zones for application. Many herbicide labels contain specific warnings and suggest measures for reducing the likelihood of drift of the product. Some herbicides actually have restricted or buffer zone requirements. Application within that restricted area would be a violation of federal law.