Spring Weed Control In Grass Hay And Pasture

By Jessica A. Williamson

Now is the time to scout grass pastures and hay in search of winter annual and biennial weeds. Both of these types of weeds are potentially susceptible to control right now and an effective herbicide application will prevent flowering and seed production. Management of perennial weeds such as dandelion, Canada thistle and the woody perennials such as multiflora rose and autumn olive is best performed a bit later in early summer after plants reach the bud-to-bloom stage. Winter annuals including the mustard species, common chickweed, horseweed/marestail, deadnettle/henbit, fleabane, etc. are growing rapidly and have already or will begin to flower and set seed very soon.

Biennials including musk and plumless thistle, burdock, wild carrot, etc. should be treated before they begin to bolt and the smaller the better. (Late fall or early spring is really the best time to treat them). The most common herbicides used for control of many broadleaf weeds in grass hay/pasture this time of year are the plant growth regulator herbicides such as 2,4-D, dicamba (Banvel, Clarity, etc.), triclopyr products (Crossbow, Garlon, etc.), and clopyralid (Stinger, PastureGard, etc.). In addition products containing metsulfuron (Cimarron, other generic formulations, etc.) can provide good control of many broadleaf weeds in the spring. (Be cautious, if forage grasses were recently seeded and are not yet established many of these herbicides can cause severe crop injury.)

Secondly, many of you know that Prowl H2O now has a supplemental label for use in cool and warm season forage grasses to control certain annual grasses and broadleaf weeds. This has been a much anticipated label since it allows for better control of weedy annual grasses such as crabgrass, foxtails, panicum, stiltgrass, etc. and others in grass forage settings.

Prowl H2O may be applied to established perennial forage grasses (including Kentucky bluegrass, bromegrass, tall fescue, orchardgrass, perennial ryegrass, timothy, switchgrass, and others) grown for forage, green chop, silage, hay production, and/or grown in pastures for livestock grazing.

• Apply at a broadcast rate of 1.1 to 4.2 quarts of Prowl H2O per acre in a single application or sequential applications made 30 or more days apart. Herbicide must be applied before weed germination in spring, or in-season between cuttings, otherwise weeds will not be controlled. Prowl H2O maybe tank-mixed with other labeled herbicides.
• Prowl H2O may be applied to mixed stands of established cool-season forage grasses and alfalfa (established alfalfa is defined as alfalfa planted in fall or spring which has gone through a first cutting/mowing). DO NOT apply Prowl H2O to mixed stands of cool-season forage grasses with other forage legumes besides alfalfa.
• There is no preharvest or pre-grazing interval for Prowl H2O-treated grass forage, green chop, silage, hay, or pasture.
• Mixed stand alfalfa/cool-season forage grasses may be grazed or harvested for forage or hay 14 or more days after applying Prowl H2O.

Weeds can be managed culturally through mowing, grazing, and proper nutrient management. Implementing a rotational grazing system has been shown to reduce weed populations by lessening the option for selective grazing. Selective grazing – or spot grazing – encourages the encroachment and spread of weeds into areas that have been overgrazed, leaving the desirable forage less competitive against the undesirable weeds, as well as allowing the avoidance of areas with weeds during grazing, causing them to further populate a pasture instead of being grazed. Continuous grazing systems often promote these grazing behaviors, leading to a greater weed population than in rotational grazing systems, where livestock are confined to a smaller grazing area, leading to less selectivity and more grazing of or near weeds. Better control of residual height, the elimination of selective grazing, as well as a more even distribution of manure and urine all help to reduce weed populations in managed grazing systems.

Mowing has been shown to help reduce weed populations when mowed at the proper time according to weed and forage growth stage and life cycle. Pastures and hay fields should be mowed before weeds set seed so after they are mowed, the seed is not viable and therefore worsens the situation. Some weeds have been shown to become worse after mowing if they are perennial and spread through rhizomes – an underground creeping root system that sends shoots upward. It is important to know weed identification to ensure mowing will not worsen the problem. Allowing a residual height of at least 3” in most cool season perennial grasses will allow forages to be tall enough to photosynthesize while keeping their root masses to absorb water and nutrients – essential for them to out-compete weeds.

Ensuring that soil fertility is optimum for forage production is another way to help with the reduction of weed populations within hay and pastures. By providing the proper nutrients and ensuring the pH is optimum, the desired forages are able to out-compete weeds.

Source:psu.edu