How can I prevent thistles in alfalfa?
Answer: The presence of weeds in an established forage crop or pasture is usually a sign of a management problem. Fertility, proper planting procedure, and harvest management are the most effective ways to maintain dense, productive pastures. Ensure adequate soil fertility and optimum pH with nitrogen-fixing legumes and applications of lime if your soil test indicates a need. When establishing new pastures, ensure that you use weed-free seed on a well-prepared seedbed, or use a no-till drill at the appropriate time. Also, be sure to practice good harvest management, whether grazing or haying, by leaving enough forage standing after harvest to allow for regrowth. It is especially important to rest pasture plants after grazing to allow full regrowth, thereby ensuring plant health and productivity.Consider the following for establishing a weed-free forage crop:? Control weeds prior to planting with successive tillage. This allows weeds to germinate, which can be killed by the next tillage. Some growers use a broad spectrum herbicide to control weeds prior to planting.? Apply lime and fertilizers according to soil test, and incorporate with tillage.? Prepare a good seedbed, with no large soil clumps.? Select weed-free certified seed.? Plant with a drill, or broadcast at a higher seeding rate and drag the field with a harrow to obtain seed to soil contact. Good seed to soil contact ensures good germination and seedling growth.? If weeds occur in the stand, mow them high. Grasses have their growing points at the base of the plant prior to flowering, and weeds like thistles have their growing points higher on the plants. Mowing creates an environment that favors grass growth over weed growth, given proper fertility management.To learn more, check out the ATTRA publication Thistle Control Alternatives, available at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=143. This publication focuses on the cultural, biological, organic, and least-toxic methods available for two of the more troublesome thistles (Canada and musk), with some coverage of other thistles such as plumeless, Italian, bull, and yellow star. Additionally, since thistles are a widespread problem, most Extension offices around the country have guidelines on thistle control and management. Check with your local Extension office for their recommendations.