UGA Forage Extension Team

Weed control in pastures and hayfields

By Steve Morgan
Harris County CEC

Weeds can reduce the quantity and the stand life of desirable forage plants in pastures and hayfields. Weeds also impact the aesthetic value of a pasture. Therefore, producers may choose to initiate weed management strategies that reduce the impact of weeds on forage production.

The first step in effective weed control is to evaluate the pasture or hay field to determine the source of the weed problem. Soil testing to determine the current nutrient and pH status is the place to begin. After correcting fertility levels, the following things must be evaluated and corrected:
• Stocking rate to eliminate overgrazing problems
• Pasture rotation schedule
• Need for additional grazing land
• Prevent scalping and mowing-too-low
• Correct the mower height in order to leave adequate stubble
• Consider renovation where forage stands are very weak

First, a weed is defined as any plant growing where you don’t want it. Therefore, we must begin to think in a broader sense as to what weeds are. A weed can be Bahiagrass or Crabgrass growing in a Bermudagrass hayfield. These unwanted plants are often more aggressive than existing or desired forage species and compete for light, water, and nutrients. In latter stages of maturity, weeds can also reduce the quality and palatability of the forage available for livestock grazing. However, not all weedy plants are detrimental to pastures. In fact, some weedy plants provide nutritional value to grazing animals.

Grazing can be used as an effective weed management tool. Livestock will graze weeds when they are small. In the early vegetative stage of growth, many weeds have nutritive values equal to or greater than the desired forages. However, the forage quality of weeds decline rapidly as the plants mature.

Mowing is especially effective in reducing the amount of weed seed produced by established broadleaf weeds. The mower should cut as close to the ground as possible. Mowing may not completely eliminate weed seed production, since some seed could be produced by plants that regrow from tillers present on grasses below the height of cutting. Also, perennial weeds that spread by underground rootstocks, like thistle, are not effectively controlled by a single mowing.

Another control method includes various herbicides that are available to provide broad-spectrum weed control. When making your selection try to choose a product that will control as many weeds as possible. This reduces the use of herbicides and also minimizes cost by reducing the number of passes through the field. When applying multiple products choose products that can be mixed in the same tank and applied in one pass.

Two popular types of weed control products are pre-emerge and post-emerge herbicides. Pre-emerge herbicide must be applied before the weed seeds germinate. An example of a pre-emerge product is Prowl H2O. This herbicide is used to control Crabgrass in Bermudagrass hayfields. Post-emerge products are used to kill weeds after they have germinated. These herbicides must be used when the plant is actively growing and not simply green.

When using any herbicide, it is important to be aware of the surrounding crops. Drift from many of these herbicides are lethal to other crops like vegetables, shrubs and flowers. Pesticide spray drift is the movement of pesticide dust or droplets through the air at the time of application or soon after, to any site other than the area intended. They should choose a product that will not harm surrounding crops if drift occurs. Drift will vary with boom height, nozzle type, pressure, and wind.

Most herbicides have grazing and feeding restrictions stated on the label that limit the use of the crop for livestock feed. Producers should know and adhere to any grazing or haying restrictions.
These restrictions can be anywhere from seven days to one year. Different products vary in their restriction guidelines. Many products that have no grazing restrictions for beef cattle will have grazing restrictions for dairy cattle. Most will also have a withdrawal period before slaughter.

Herbicides can be a useful tool for weed management in pastures and hayfields. They should be used where appropriate and when cost effective. 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.