Published on Wednesday, September 30, 2020
Winter annuals will germinate in the fall, overwinter, and produce seed in early spring and summer. Common examples include marestail, henbit, purple deadnettle, prickly lettuce, common chickweed, shepherd’s purse, pennycress, etc. Most winter annuals will overwinter as a rosette and bolt in the spring, producing seed in early summer. However, marestail can have extended germination which can result in additional flushes of weeds in the spring and even early summer.
For summer annuals, the goal is to prevent seeds from being added to the seed bank. For winter annuals, we must not only prevent new seeds from being added to the seed bank but also prevent them from becoming a host plant. Winter annuals also provide an ideal overwintering site for soybean cyst nematode (SCN). Winter annuals like common chickweed also provide the ideal environment for black cutworms to lay their eggs in early spring. If these pests plague your field, weed management becomes more critical in the fall.
Glyphosate will control many of these winter annuals. However, some winter annuals like marestail have developed resistance to glyphosate. In that case, using other burndown herbicides such as growth regulators can be very effective. If applying in the fall, 2,4-D, tank-mixed with glyphosate, can be a cost-effective method to control winter annuals. In heavy marestail pressure, a 2,4-D + dicamba product like Brash® or WeedMaster®, when tank-mixed with glyphosate, can provide effective control. If annual bluegrass is not a concern, substituting glyphosate with metribuzin as the tank mix partner with Brash or Weedmaster will provide another SOA against GR marestail. Some residual products are also labeled for fall applications. The downside to these products would be the higher cost and limited residual value in the spring.
Author: Joe Bolte
Categories: Agronomy, Agronomy Talk