Part 2, Section 6: Forages Pest Management
Forages Pest Management
Managing weeds in forages requires a different approach from managing weeds in row crops. Over 95 percent of weed control in a healthy forage crop comes from competition provided by the forage. To maintain a relatively weed-free forage, however, proper fertilization, cutting management, and insect control, as well as using disease-resistant varieties and selective herbicides, will keep the forage stand competitive.
If weeds become a problem, they can compete for or interfere with light, nutrients, water, and space, directly influencing yield and standability. Common chickweed infestations in alfalfa have been reported to reduce forage stand by more than 30 percent. Common chickweed emerges in the fall and winter, and develops a thick, lush mat early in the spring that can compete with the first forage cutting. Once the chickweed dies in early summer, summer-annual weeds such as foxtails, lambsquarters, and pigweed, or perennial weeds such as dandelion can replace the dead or dying winter-annual weeds and continue to reduce forage yield and quality.
Unlike most grain or fiber crops from which weeds are separated at harvest, weeds often are harvested along with the forage crop, potentially reducing quality. Reductions in quality often are in the form of lower protein content and feed digestibility. Although weeds do have some feed value, this value differs among species. Dandelions come close to equaling alfalfa in protein and total digestible nutrients (TDN). Dandelion control may not necessarily improve the quality of hay, but it may be of some value in reducing the time necessary to dry the hay, since dandelion dries more slowly than alfalfa. Increased drying time may mean greater harvest losses due to untimely rainfall.
Grassy weed quality can be similar to that of the forage. In general, weedy grasses have about 75 percent of the quality of alfalfa; however, controlling quackgrass in alfalfa can increase forage protein levels 4 percent to 7 percent. Weeds with woody stems or flower stalks, such as yellow rocket, white cockle, rough fleabane, curly dock, and broadleaf dock, have lower protein levels (about 50 percent of the quality of alfalfa), so controlling them is even more important.
When weeds are present or persist in spite of good management, herbicides can help improve yield and quality. Herbicides available for use in legume or grass forages and pastures are listed in Table 2.6-1. Weed control at establishment or in the seedling year is most critical for maintaining a healthy forage stand. When weeds are controlled during the seedling year, the forage crop seldom requires additional herbicide treatments for at least the first two years of the stand.
Weed management in forages can be divided into two phases: control in the establishment or seedling year and control in an established stand.