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Issue No. 6, Article 13/May 5, 2006

Dry Soils and Grass Escapes in Corn

In many areas of Illinois, preplant and preemergence corn herbicides have been on the ground anywhere from a few days to several weeks without adequate precipitation to move the herbicides into the soil solution. Herbicide effectiveness can be significantly reduced when a soil-applied herbicide is sprayed on a dry soil surface with no incorporation (mechanical or by precipitation) for several days following application. How much rainfall is required to move the herbicide into the soil, and how soon after application is precipitation needed? While there is no absolutely defined amount, surface-applied herbicides generally require between 0.5 and 1.0 inch of precipitation within 7 to 10 days after application for "activation." Factors such as soil condition, residue cover, and the chemical properties of the herbicide influence how much rain is needed and how soon after application it is necessary. If weeds have begun to emerge before the herbicide has been moved into the soil solution, it may be time to consider additional management options. Rotary hoeing (see "Remember the Rotary Hoe?" in this issue) can control small emerging weeds and give surface-applied herbicides some incorporation. Several postemergence herbicides for grass control in corn are described in the following paragraphs. Table 3, reproduced from the 2006 Illinois Agricultural Pest Management Handbook, provides grass control ratings for several postemergence corn herbicides.

Basis 75WDG (rimsulfuron + thifensulfuron) can be applied at 1/3 ounce per acre to field corn from spike through the 4-leaf (2 collars) stage for control of 1- to 2-inch barnyardgrass, foxtails, and fall panicum. Do not apply to corn having three fully emerged collars or over 6 inches tall. Applications of Basis must include a crop oil concentrate (COC; petroleum or methylated seed oil) or a nonionic surfactant (NIS). An ammonium nitrogen fertilizer must also be added with the COC or NIS. The Basis label includes precautionary statements about making applications to corn previously treated with certain soil insecticides.

Basis Gold 89.5WDG (nicosulfuron + rimsulfuron + atrazine) can be applied at 14 ounces per acre to control foxtails, barnyardgrass, and fall panicum up to 3 inches tall, shattercane up to 6 inches, and quackgrass and seedling johnsongrass up to 8 inches. Several other grass and broadleaf weed species also are listed on the label. Applications of Basis Gold must include a COC (petroleum- or vegetable-based), and addition of an ammonium fertilizer is recommended. Basis Gold may be applied to corn up to 12 inches. Do not apply to corn taller than 12 inches or exhibiting more than 6 leaf collars, whichever is more restrictive. The Basis Gold label includes precautionary statements about making applications to corn previously treated with certain soil insecticides.

Accent Gold 78.1WDG (clopyralid + flumetsulam + nicosulfuron + rimsulfuron) can be applied at 3.5 ounces per acre to control foxtails, barnyardgrass, and fall panicum up to 3 inches tall, shattercane up to 6 inches, and quackgrass and seedling johnsongrass up to 8 inches. Several other grass and broadleaf weed species also are listed on the label. Applications of Accent Gold must include either a COC (petroleum- or vegetable-based) or NIS, plus an ammonium fertilizer is recommended. Accent Gold may be applied to corn up to 12 inches. Do not apply to corn taller than 12 inches or exhibiting 6 leaf collars, whichever is more restrictive. The Accent Gold label includes precautionary statements about making applications to corn previously treated with certain soil insecticides.

Steadfast 75WDG (nicosulfuron + rimsulfuron) can be applied at 3/4 ounce per acre to control foxtails, barnyardgrass, and fall panicum up to 4 inches tall, shattercane up to 6 inches, quackgrass up to 8 inches, and johnsongrass up to 12 inches. Steadfast may be applied to corn up to 20 inches or through the V6 stage, whichever is more restrictive. Applications must include a COC or NIS, as well as an ammonium nitrogen fertilizer. The Steadfast label includes precautionary statements about making applications to corn previously treated with certain soil insecticides.

Steadfast ATZ 89.3WDG (nicosulfuron + rimsulfuron + atrazine) can be applied at 14 ounces per acre to corn up to 12 inches tall or through the V6 stage, whichever is more restrictive. Grass species and sizes listed on the Steadfast ATZ label are nearly identical to those listed on the Steadfast label. Applications must include a COC or NIS, as well as an ammonium nitrogen fertilizer. The Steadfast ATZ label includes precautionary statements about making applications to corn previously treated with certain soil insecticides.

Accent 75WDG (nicosulfuron) can be applied broadcast to corn up to 20 inches tall or through the V6 stage, whichever is more restrictive. Similar to other ALS-inhibiting corn herbicides, the Accent label cautions about applications to corn previously treated with certain soil insecticides. Celebrity Plus 70WDG is a premix containing nicosulfuron and controls many of the same grass weed species as Accent.

Option 35WDG (foramsulfuron) can be applied broadcast at 1.5 to 1.75 ounces per acre to corn at least V1 and through the V6 growth stage. Applications of Option must include a methylated (MSO) or ethylated (ESO) seed oil and an ammonium nitrogen fertilizer. The 1.5-ounce rate of Option will provide control of barnyardgrass up to 4 inches tall, green or yellow foxtail and fall panicum up to 3 inches, giant foxtail up to 6 inches, and shattercane up to 12 inches. Several other annual and perennial grass weed species are listed on the label. The Option label includes precautionary statements about making applications to corn previously treated with certain soil insecticides.

Equip 32WDG, a premix containing foramsulfuron, controls many of the same grass weed species as Option. Grass sizes on the Equip label are generally smaller than those listed on the Option label.

Beacon 75WDG (primisulfuron) can be applied broadcast to corn between 4 and 20 inches tall. Corn plants less than 4 inches may be more susceptible to injury. Applications should include a COC or NIS; a liquid nitrogen fertilizer may also be included. Beacon is effective on shattercane, johnsongrass, and quackgrass but is weaker than Accent on other annual grass weed species. NorthStar 47.4WDG and Spirit 57WDG are premixes containing the active ingredient of Beacon plus dicamba or prosulfuron, respectively. While primarily used for broadleaf weed control, these herbicides can also provide control of certain annual and perennial grass weed species. These labels also carry precautionary statements regarding applications to corn previously treated with certain soil insecticides.

Atrazine can be applied as a post-emergence treatment before corn exceeds 12 inches to control certain annual grasses (not fall panicum) up to 1.5 inches tall. Include a COC with postemergence atrazine applications.

Other postemergence corn herbicides that will control grass weed species, including glyphosate (premixes containing glyphosate include Expert, FieldMaster, and ReadyMaster ATZ), Liberty, and Lightning, require the planting of herbicide-resistant corn hybrids.--Aaron Hager and Dawn Nordby

Authors:
Aaron Hager
Dawn Refsell

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