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Fall weed control

Agronomy Bulletin 114-- Fall Herbicide Application

Dandelions and many winter annuals are better controlled in the fall rather than in spring, when cool weather can slow herbicide activity.

Situation

Difficult-to-control and herbicide-resistant weeds are major issues facing crop farmers. Troublesome weeds sometimes get a head start by popping up in the fall. Although tillage can take care of problem weeds, it isn’t always preferred or even possible. A well-timed fall herbicide application can prevent weeds from getting a head start and save time during the busy spring season.

Factors to Consider

  • Winter annual weed infestations
  • Perennials and biennials
  • Herbicide modes of action
  • Use of cover crops or tillage
Fall herbicide applications are good options to manage difficult-to-control weeds, such as marestail.

Action Plan

  1. Evaluate the best weed control solution. If a reduced tillage or no-tillage program puts too much pressure on spring/summer weed control, fall applications can be a good alternative.Fall herbicide applications often are a good solution for challenging weeds, such as marestail, especially if the weeds are difficult to control in crop. Additionally, fall herbicides can control winter annual weeds that harbor insects and increase unwanted nematodes. Other benefits of fall applications include better control of cool-season perennials, legumes and cool-season grasses, if rotations allow, and better activity of glyphosate on established dandelion and winter annuals compared with application in spring.
  2. Select herbicides. A fall burndown combination of glyphosate and 2,4-D or of glyphosate and a combination of phenoxy herbicides, such as dicamba, and 2,4-D typically provide adequate control of tough-to-control weeds and winter annuals. The cooler temperature and more stable weather in fall make it an excellent time to use phenoxy herbicides such as dicamba to minimize off-target movement and drift. Hold off on residual herbicide applications until spring to catch any late weed escapes.
  3. Determine application timing. Wait at least two weeks after grain harvest for regrowth of vegetation or newly emerged weeds. Residue can reduce herbicide coverage, and winter annuals might not have emerged at harvest. Make applications a couple of weeks after a killing frost but before a hard freeze. Do not make applications to frozen ground or in freezing weather, because results will be less than satisfactory.
  4. Target problem fields first. Start applications in fields that have had weed problems such as marestail in crop.
  5. Use the correct additives. In cool weather conditions (cooler than 60 F), additives can help ensure better herbicide uptake.

Summary

Fall herbicide applications can effectively manage problem weeds when tillage isn’t an option and controlling weeds in crop is difficult. For more information, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser.

Published on Wednesday, August 07, 2013