By Gene Schmitz, University of Missouri Extension Livestock Specialist
Lingering effects of the drought of 2012 include a reduction of desirable forage grass species and an increase in broadleaf weeds in pastures and hay fields. Below are some comments taken from the MU Weed and Brush Control Guide regarding weed management in pastures and hay fields.
Herbicide application timing varies with weed species. As a general rule, annual weeds are controlled most effectively with herbicides when they are small and actively growing. For winter annuals, this corresponds to a late fall to early spring timeframe while for summer annuals, this usually corresponds to late spring or early summer.
For biennial weeds (two-year life cycles), the optimum time for herbicide application is when these weeds are in the rosette stage of growth. This corresponds to fall or early spring for most biennial weeds that occur in pastures and rangelands in Missouri.
Established perennials are most susceptible in the bud to bloom stage, which often occurs in the early fall when food reserves are moving into the roots. Woody brush species should be sprayed when they are fully leafed out and actively growing. Optimum control will usually be achieved by clipping brush species in the fall and treating young shoots that are fully leafed out in the spring. However, it is important to keep in mind that multiple applications may be needed over several years to obtain complete control of perennial and woody brush species.
Forage legumes are frequently grown with a companion crop such as orchard grass. However, most herbicides registered for use in forage legume will severely injure or kill a grass companion crop. Conversely, most herbicides registered for use in grass pastures will injure or kill forage legumes. If the weed problem is severe, reestablishment may be necessary.
Probably the biggest reason for not spraying broadleaf weeds in pastures is the loss of the legume component in the stand. However, there are times when either the weed pressure is so large or the legume component so small that loosing the legumes is probably worth it in the long run. Reducing weed pressure can lead to increased grass production. MU research also shows beef cattle prefer grazing in areas that have been treated for broadleaf weeds compared to unsprayed areas in the same pasture.
Remember, if you invest in chemical control of weeds, you also need to change the management to encourage the desired species. This may mean additional fertility, a change in grazing management, reseeding or a combination of all of these.
We do have many useful chemical tools available for pasture weed control. Proper timing and application rates are important parts of a successful weed control program. Contact me at the Extension Center in Warsaw at (660) 438-5012 or your local Extension Center for more information on this topic. University of Missouri Extension is an equal opportunity / ADA institution.