• Topics: Agronomy  | Weed Management in Field Crops and Pasture Grasses (WMG)  | Small Grain Pest Management  | Small Grains  | Field and Forage Crops  |  Ferrell, Jason A  |  Brecke, Barry J  |  MacDonald, Gregory 

Weed Management in Small Grains Harvested for Grain - 2007¹

Successful weed control in small grains involves using good management practices in all phases of production. In Florida, winter weeds compete with small grains for moisture, nutrients and light with the greatest amount of competition occurring during the first six to eight weeks after planting. Weeds also cause harvest problems the following spring when the small grain is mature.

Crop Competition

Crop competition is one of the most important, but often one of the most overlooked tools in weed control. A good small grain stand which emerges rapidly and shades the soil surface is helpful in reducing weed competition.

Utilizing good management practices is necessary for producing maximum small grain yields and is also an aid in weed control. The plant that emerges first and grows most rapidly is usually the plant that will have the competitive advantage; therefore, everything possible should be done to ensure that the small grain, not the weed, has this competitive advantage. For optimum management practices, follow Florida Cooperative Extension Service recommendations.

Know Your Weeds

Know your weeds and choose the herbicide that is effective for your specific weed problem (Table 2). In Florida, small grains are infested with several species of winter weeds most of which can be controlled by the phenoxy type herbicides, namely 2,4-D. However, some species that inhabit Florida small grain fields may not be controlled by 2,4-D. Proper identification is crucial for controlling wild radish (Raphanus raphanistrum) which is often confused with wild mustard (Brassica kaber). Wild radish is ubiquitous throughout Florida and is not easily controlled with 2,4-D. Table 2 provides herbicide effectiveness on weed species. Wild mustard occurs sparsely within the Florida small grain growing region and can easily be controlled with applications of 2,4-D. Most producers refer to both species as "Wild Mustard," therefore compounding the identification problem. If wild radish is misidentified, the degree of weed control given by 2,4-D applications may be inadequate. It should be understood that 2,4-D does have activity on wild radish but the restriction of 2,4-D applications tied to small grain size usually allows the wild radish to get too large to be controlled. Wild radish can be controlled by 2,4-D up to 6 inches or the 3-leaf stage. The confusion of wild mustard and wild radish is the most notable instance where a misidentification can cause sub-standard weed control in small grains.

Chemical Control

Proper choice of the herbicide and rate applied are extremely important for weed control in small grains (Table 1). Postemergence herbicides combined with the previously discussed management practices are important for ensuring that the small grain crop has the initial competitive edge. Herbicide applications should be made to small weeds unless specifically stated on label or recommendations.

The most widely used herbicide in small grains is 2,4-D. Small grains vary in their tolerance to 2,4-D depending upon the growth stage when the herbicide is applied and the particular crop planted (Table 1). Generally wheat varieties are the most tolerant, barley is intermediate, and oats are least tolerant to 2,4-D. Rye is intermediate between wheat and barley. As a general rule the least injury to the grain crop with the use of 2,4-D can be expected when it is applied from the 3-4 tiller to full tiller stage. Applications made after jointing will result in grain head injury and possible reduction in seed fill.

Most herbicides labeled for weed control in small grains belong to or are similar to the organo-auxin herbicide group and do have some potential for off-target spray drift. Care should be taken to avoid spray drift to sensitive crops. Furthermore, the State of Florida has restrictions and prohibitions on organo-auxin herbicides used within the state. Refer to fact sheet SS-AGR-12 Florida's Organo-Auxin Herbicide Rule for information concerning this rule.

The herbicides suggested are those that have performed well in IFAS research. Read and follow all label instructions and precautions. Accurate sprayer calibration is extremely important since rates too low may not provide adequate weed control and rates too high may injure the crop. Herbicides, like any pesticide, should be handled with care. Store herbicides behind locked doors in the original containers with the label intact and separated from seed, fertilizers and other pesticides.

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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