Annual Grass Control
One or more species of annual grasses are usually present in soybean fields. Annual grasses are not nearly as competitive with soybeans as are most broadleaf weeds. Annual grasses are more competitive when growing in the row middles than when growing in the soybean row. If the row middles can be kept clean for four or more weeks after planting, soybeans can tolerate rather high populations of most annual grasses in the row. Thus, timely cultivations may give sufficient annual grass control.
Annual grasses can be controlled with preplant incorporated, preemergence, and postemergence herbicides. The soil-applied broadleaf herbicides such as Canopy, Lexone, Lorox, Scepter, and Sencor give suppression of some annual grasses. With light infestations of susceptible species, one of these broadleaf herbicides plus cultivation may be adequate for annual grasses. Where moderate to heavy grass infestations or nonsusceptible species are expected or where you do not plan to cultivate, a grass control herbicide is recommended.
Preplant-Incorporated Herbicides for Annual Grasses
Preplant-incorporated herbicide options for annual grasses include Command, Prowl, Sonalan, Treflan, and Vernam. Packaged mixtures containing both a grass and a broadleaf herbicide include Broadstrike + Dual, Broadstrike + Treflan, Salute, Squadron, and Tri-Scept. Dual, Lasso, and Turbo may also be incorporated, but they are generally considered to be preemergence herbicides.
Prowl, Sonalan, and Treflan are very similar and can basically be used interchangeably. They provide good to excellent control of all the common annual grasses. They also provide good control of certain small-seeded broadleaf weeds such as pigweed, lambsquarter, carpetweed, common purslane, and Florida pusley. Control is basically season-long, but carryover is not likely to be a problem unless high rates are used. See Table 5 for registered tank mixtures with broadleaf herbicides. Several generic brands of trifluralin (the active ingredient in Treflan) are available.
The labels for Prowl, Sonalan, and Treflan specify the maximum waiting period between application and incorporation (24 hours for Treflan, 2 days for Sonalan, 7 days for Prowl). It is best to incorporate these herbicides as soon as possible after application. A delay in incorporation can result in a significant herbicide loss. Incorporate about 2 to 3 inches deep.
Command gives season-long control of annual grasses except shattercane and Texas panicum, and it controls several broadleaf weeds. Note, however, that Command does not control pigweed.
Command may be preplant incorporated or applied preemergence. Off-target movement, due to both spray drift and vapor drift, can be a significant problem with Command. Many types of fruit trees, ornamentals, vegetables, and native vegetation are very sensitive to minute amounts of Command. The Command label lists detailed application guidelines to reduce spray drift, such as use of a drift control agent; specific nozzles, pressures, spray volumes, and boom heights to use; and limitations on wind speed. The label also lists specific buffer zones (up to 1,500 feet) that must be maintained between Command-treated fields and city limits, houses, commercial fruit and vegetable production facilities, and desirable vegetation in general. Users of Command are strongly urged to follow all precautions on the Command label to avoid damage to off-target vegetation.
Off-target movement of Command due to vapor drift is a greater concern than spray drift because vapor drift can damage sensitive vegetation over much greater distances. The only way to curtail vapor drift is to incorporate the Command. To minimize off-target movement, Command should be incorporated immediately after application. Weed control will be better if the Command is incorporated shallowly.
After using Command, thoroughly clean the sprayer before using it on other crops. Certain agronomic and horticultural crops are very sensitive to minute amounts of Command. The label specifies the proper sprayer cleanout procedure.
Vernam controls annual grasses except broadleaf signalgrass and Texas panicum. Small-seeded broadleaf weeds such as pigweed, lambsquarter, carpetweed, common purslane, and Florida pusley are also controlled. Vernam normally provides control for about four weeks. Combined with a competitive crop canopy and cultivation if needed, this control period should be long enough in soybeans.
Vernam should be incorporated immediately after application. A short delay in incorporation (15 minutes or less) can result in significant volatilization losses and reduced weed control.
Broadstrike + Treflan, Salute, Squadron, Tri-Scept, and Turbo are packaged mixtures of grass and broadleaf herbicides. Broadstrike + Treflan contains flumetsulam plus trifluralin (the active ingredient in Treflan). Salute contains trifluralin plus metribuzin (the active ingredient in Sencor). Turbo contains metolachlor (the active ingredient in Dual) plus metribuzin. Squadron contains pendimethalin plus imazaquin (the active ingredients in Prowl and Scepter, respectively). Tri-Scept contains trifluralin and imazaquin. See Table 14 and the most recent labels for rotational restrictions on Broadstrike + Treflan, Squadron and Tri-Scept.
Pursuit Plus is a packaged mixture containing pendimethalin and imazethapyr (the active ingredients in Prowl and Pursuit, respectively). Although registered for preplant-incorporated application, Pursuit Plus is generally not recommended in North Carolina. Broadstrike + Treflan, Squadron, Tri-Scept, or a tank mixture of Prowl, Sonalan, or Treflan plus Canopy or Scepter is a better option in most cases for growers who want to apply a preplant-incorporated grass and broadleaf herbicide.
Preemergence Herbicides for Annual Grasses
Preemergence herbicide choices for annual grass control include Command, Dual, Lasso, Lasso Micro-Tech, Partner, and Prowl. Packaged mixtures containing both a grass and a broadleaf herbicide include Broadstrike + Dual, Squadron, and Turbo.
Command applied preemergence controls all common annual grasses except shattercane and Texas panicum. It is particularly effective on broadleaf signalgrass. In addition, it controls several broadleaf weeds. Note that it does not control pigweed.
Significant off-target movement and damage to susceptible vegetation may occur when Command is applied preemergence. To reduce this problem, the Command label prohibits preemergence application within 1,500 feet of desirable vegetation. See the Command label for details.
Dual and Lasso provide good to excellent control of common annual grasses except Texas panicum, seedling johnsongrass, and shattercane. Dual and Lasso also control pigweed but often are inadequate on lambsquarter. In conventional tillage systems, control with Lasso and Lasso Micro-Tech will be similar. In no- till with heavy residue, Lasso Micro-Tech may perform somewhat better than Lasso EC. Partner is a 65 percent water dispersible granular formulation of alachlor (the active ingredient in Lasso). Performance should be similar to that obtained with Lasso.
Prowl is registered for preemergence application alone or in mixture with certain broadleaf herbicides. Prowl performs better and more consistently when incorporated than when applied preemergence. Prowl applied preemergence often does not adequately control moderate to heavy infestations of annual grasses.
Broadstrike + Dual is a packaged mixture containing flumetsulam and metolachlor (the active ingredient in Dual). Turbo is a packaged mixture of metolachlor and metribuzin (the active ingredient in Senecor). Annual grass control with these packaged mixtures should be similar to that attained with a similar rate of Dual applied alone. Squadron, a packaged mixture containing pendimethalin plus imazaquin (the active ingredients in Prowl and Scepter, respectively) may be preplant incorporated or applied preemergence. Preplant-incorporated application is preferred. Pursuit Plus, a packaged mixture of pendimethalin plus imazethapyr (the active ingredients in Prowl and Pursuit, respectively) is registered for preemergence application but is generally not recommended in North Carolina.
Postemergence Herbicides for Annual Grasses
Herbicide options for postemergence control of annual grasses include Assure II, Bugle, Fusilade DX, Poast, Poast Plus, and Select. When properly applied, these herbicides control annual grasses well. Exceptions include Poast and Poast Plus applied to crowfootgrass.
Poast and Poast Plus contain the same active ingredient. Poast Plus contains additional adjuvants that may somewhat enhance control under marginal conditions.
Two applications of any of the six products may be made; however, one properly timed application in combination with a competitive row spacing or cultivation should be sufficient. The optimum grass size for application depends upon the product being used and the species of grass being treated. Application to larger grasses, especially if under drought stress, may result in insufficient control. Cultivation will enhance control, but to avoid stressing the grass, do not cultivate within 5 to 7 days before or after application.
These postemergence grass herbicides can be tank mixed with most broadleaf herbicides