Everyone knows weeds in bermudagrass pastures are bad. Weeds reduce yields by competing with grass for available sunlight, nutrients and water; drive up costs by reducing fertilizer use efficiency and requiring additional inputs; reduce forage quality and palatability; lower nutrient content and could even be toxic. The question is, what are you going to do about it?
The most effective weed control measures are those that manage weeds before they cause an economic loss. A few factors affecting the choice of control strategies include the target weed species, growth stage of the weeds, weather conditions, growth stage of the bermudagrass and method of forage utilization. Weed control can be achieved with cultural practices, herbicides or a combination of both.
The first tool in a successful bermudagrass weed control strategy is a good fertility program. This begins with collecting a soil sample to determine how much of each nutrient is needed. The Noble Research Institute has a video, "Unless You Test, It's Just a Guess," that discusses soil testing and demonstrates correct soil sampling procedures. It is available by calling (580) 224-6480. If provided with optimum fertility and adequate rainfall, established bermudagrass can do an excellent job of choking out many weeds. A healthy stand of bermudagrass will often be enough to prevent a significant weed problem from developing.
Haying or grazing strategies also have a significant impact on the weed populations. In order to minimize the opportunity for weeds to develop, bermudagrass should be allowed to maintain good canopy coverage while removing the majority of new growth about every three to four weeks. Removing this growth will allow more light to reach the lower leaves, stimulate sod growth and provide better-quality forage. If the bermudagrass is being cut for hay, be sure not to cut it too close to the ground in order to leave some canopy for the grass to regenerate itself. If grazing, closely monitor the stocking rate and use rotational grazing to maximize your forage use efficiency. This is especially important when going into winter or during summer drought stress.
Once the bermudagrass is being managed for optimum efficiency and health, it is time to turn your attention to the weeds. First, identify the weed species and their life cycles to determine the best approach to their control. Are they grasses or broadleaves? Annuals or perennials? Warm season or cool season? All of these factors must be considered when developing a weed management strategy.
For information on weed control strategies in newly sprigged bermudagrass, refer to Jeff Ball's article in the January 2005 issue of NF Ag News and Views. In established bermudagrass, there are several options for chemical weed control strategies. There are dormant-season applications of non-selective herbicides to control emerged winter weeds. You may choose to make a spring or summer application to control warm-season species. Or you have the choice of a fall application to control perennial weeds. The strategy chosen will depend on the target weed species and when it is most susceptible to herbicidal control.
When using herbicides for post-emergence weed control, make certain that the weather and target weed conditions are favorable. Weeds should be within the size range specified on the label and actively growing. Weeds under stress do not absorb herbicides well, and this often results in reduced control. The weather conditions during application should be favorable with respect to wind speed and direction, temperature and forecast for rainfall. Forcing an application when the weather is adverse is a recipe for a weed control failure.
Another consideration when planning a weed control strategy is how the forage production will be utilized. Many herbicides have restrictions for time until a treated pasture can be grazed or cut for hay, exclusion of lactating animals from treated fields or restrictions on time from consuming treated forage or hay before slaughter. Always read and follow the label directions to ensure that your herbicide use decisions don't interfere with your utilization plan.
If you have questions about weed control strategy, contact a Noble Research Institute soil and crops specialist at (580) 224-6500.