Farm Talk

October 29, 2013

Fall weed management

Sarah Kenyon

Parsons, Kansas — Weeds that form a rosette typically germinate in the fall or early spring. Plants that form a rosette include: Thistles, dandelion, Queen Anne's lace, chicory, spotted knapweed, red sorrel, poison hemlock, and others. Because of their low, spreading growth, these weeds can smother the grass and create open spaces in the pasture. In addition to decreasing forage quality, weeds like Queen Annes's lace, chicory, and dock can gum up fescue seed combining equipment and create more trash in the gleaned seed.

Fall and early spring is one of the best times of the year to control rosette-forming weeds and other winter annual weeds. Make sure spraying occurs on days where the high temperature is a minimum of 60 degrees F, there is no hard freezing at night, and plenty of sunshine.

The most common thistles that occur in southern Missouri are muck, bull, and tall thistles. Control is best achieved when sprayed in the rosette stage, from October through April. Use products that contain 2,4-D, have dicamba as the active ingredient, Grazon P+D, Chaparral, GrazonNext HL, or Tordon 22K. If mowing, the best time is to mow within two days after the terminal flower head blooms, then repeat 3-4 weeks later. For musk thistle, do not spray during flowering; the musk thistle flower head weevil will provide the best control at that time. Thistle weevils are a help in the control process and cannot be relied on for full control.

Poison hemlock is poisonous to both humans and livestock. It can also be mistaken for Queen Anne's lace. Poison hemlock has purple/red spots on the stem and has an odor. Both weeds remain green throughout the winter, and can quickly overtake a pasture. Use Grazon P+D products, Tordon 22K, or Remedy Ultra before the plants bolt in the spring. Best control is achieved during the rosette stage in the fall or spring.

Spotted knapweed can also be controlled with fall spraying. This weed has been rapidly taking over many pastures and hayfields in southern Missouri. This is because the roots excrete a toxin that kills neighboring plants. Use Milestone, Grazon P+D, Chaparral, or Tordon 22K when in the rosette or early bud stage. Control is more effective when the plant is sprayed before it reaches a foot tall. Spotted knapweed weevils can also be released and are anticipated to provide control within a few years.

Other weeds to consider for fall spraying are henbit and chickweed. These plants germinate in the fall, grow through the winter, and produce seed in the spring. They are most common in dormant warm-season grass pastures or in new seeding, but can also be problematic in established pastures or yards. Banvil or clarity (active ingredient dicamba) mixed with 2,4-D, or Grazon P+D can be used in grass pastures. Round-up or Gramoxone can be used on warm-season grasses, like bermudagrass, after the crop is in winter dormancy.

Make sure to read the herbicide label carefully before applying, because many herbicides can damage newly germinated grass seedlings. New seedlings need to have a sufficient root system before herbicides can be applied. £