Although weeds are usually less of a problem in small grains than in row crops, heavy infestations of annual weeds, quackgrass, or wild garlic reduce grain yields and/or quality
Good cultural practices will result in a thick, heavy stand of small grains that will compete effectively with weeds during the early stages of crop development. Crop rotation, sound soil management practices, the use of certified seed of recommended varieties, proper seedbed preparation, and timely planting all contribute to weed control in small grains. Herbicides can be used to supplement these cultural practices as needed (Table 5.9.1)
Small grain fields should be checked for weeds in the fall (for winter wheat or barley) or early spring because most herbicide applications should be made prior to jointing (Growth Stage 6), or the appearance of the first node at the base of the plant (usually 4 to 8 inches tall with 12 or more leaves). Herbicide application during grain ripening may aid harvest operations but will not increase grain yields.
Many winter annual broadleaf weeds in winter wheat can be controlled with spring applications of 2,4-D or Banvel/Clarity. Both can cause crop injury if used at growth stages other than those recommended. In addition, Banvel/Clarity may delay wheat maturity when used according to guidelines.
Spring applications of 2,4-D or Banvel/Clarity are not effective against corn chamomile. Buctril is effective on corn chamomile when the rosettes (clusters of leaves in circular form) are less than 1 inch across. Corn chamomile usually reaches this stage within a month after seeding so Buctril applications for this weed should be made in the fall. Other annual weeds controlled with Buctril are field pennycress, field pepperweed, shepherdspurse, small seed falseflax, wild mustard, wild radish, and yellow rocket. Harmony Extra is a better choice for corn chamomile control than Buctril if application is delayed until spring.
Herbicide Resistance Management
Herbicide resistance management involves the use of crop rotation along with herbicide rotation and/or use of herbicide combinations that include herbicides with different sites of action (how they affect weeds). These practices will help manage existing herbicide resistant weed populations and delay development of new resistant weed populations.
To effectively utilize herbicides with different sites of action, everyone involved in decisions about weed management must have site of action classification readily available. The Weed Science Society of America (WSSA) has approved a numbering system to classify herbicides by their site of action (Mallory-Smith, C.A. and Retzinger, E.J. 2003. Revised classification of herbicides by site of action for weed resistance management strategies. Weed Technol. 17:605-619).