Weeds and forages, fortunately, are not as likely a combination as are weeds with many other crops.  Well-managed, vigorously growing grass and alfalfa are generally able to resist heavy weed infestation. But a breakdown in growth could open the door to unwanted plants, which compete for light, water and nutrients; can diminish the quality and palatability of forages; and may even be poisonous to livestock.

University of Kentucky forage researcher J.D. Green says the promotion of healthy, weed-resistant pastures and hayfields can be aided by:

  • Maintaining proper soil pH and fertility levels. Adjusting the soil pH and nutrient levels according to soil test recommendations helps increase stand density and promote good growth. However, Green cautions that this practice alone usually is not enough to eliminate weed establishment. And some weeds – such as common chickweed, crabgrass and curly dock – grow more aggressively in fertile soil.
  • Using controlled grazing practices. When grazed as young plants, weeds may be consumed readily and be an acceptable source of animal nutrition. Their nutritive value and palatability decline rapidly as they mature, however. As animals begin to avoid weeds with selective grazing, weeds such as horse nettle, thistles and tall ironweed become more prominent over time. 
  • Mowing. Timely mowing of pastures can be beneficial for suppressing growth of erect weedy grasses and many broadleaf weeds. Green suggests mowing when plants are 12 to 18 inches high, to interrupt weed growth before the plants have flowered and produced seeds. He also advises clipping vegetation as close to the soil as possible.
  • Stand renovation. Sometimes pastures and hayfields must be re-seeded to maintain proper stands. Green advises to time the new seeding according to the weeds that are at issue.  When establishing a grass-legume mixture, it may be desirable to seed the grass component in late summer or fall, and then interseed the legume species the following spring.

In addition to these cultural methods, Greed notes that herbicides can play a useful role in controlling problem weeds. For his recommendations on suitable herbicides, rates, estimated costs, timing and species control, follow this link (PDF format).