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Dry Soils and Soil-Applied Herbicides

May 4, 2001
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 to 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's 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 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.

Basis 75WDG (rimsulfuron + thifensulfuron) can be applied at 1/3 ounce per acre to field corn in the spike to 4-leaf (2 leaf 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 in height. Applications of Basis must include a crop oil concentrate (COC) (petroleum or methylated seed oil) or a nonionic surfactant (NIS). An annonium 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 89.46WDG (nicosulfuron + rimsulfuron + atrazine) can be applied at 14 ounces per acre to control foxtails, barnyardgrass, and fall panicum up to 3 inches in height, shattercane up to 6 inches in height, and up to 8-inch-tall quackgrass and seedling johnsongrass. 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 in height. Do not apply to corn taller than 12 inches or exhibiting six 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 83.8WDG (clopyralid + flumetsulam + nicosulfuron + rimsulfuron) can be applied at 2.9 ounces per acre to control foxtails, barnyardgrass, and fall panicum up to 3 inches in height, shattercane up to 6 inches in height, and quackgrass and seedling johnsongrass up to 8 inches in height. Several other grass and broadleaf weed species also are listed on the label. Applications of Accent Gold must include a COC (petroleum or vegetable based), and addition of an ammonium fertilizer is recommended. Accent Gold may be applied to corn up to 12 inches in height. Do not apply to corn taller than 12 inches or exhibiting six 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 in height, shattercane up to 6 inches in height, and up to 8-inch-tall quackgrass and seedling johnsongrass. Do not apply Steadfast to corn taller than 12 inches or exhibiting 6 leaf collars, 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.

Accent 75WDG (nicosulfuron) can be applied broadcast to corn up to 20 inches in height or that has six or fewer leaf collars, 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.

Beacon 75WDG (primisulfuron) can be applied broadcast to corn between 4 and 20 inches in height. Corn plants less than 4 inches in height 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, and 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 herbicide labels also carry precautionary statements regarding applications to corn previously treated with certain soil insecticides.

Atrazine can be used as a postemer-gence treatment before corn exceeds 12 inches in height to control certain annual grasses (not fall panicum) up to 1.5 inches in height. Include a COC with postemergence atrazine applications.

Other postemergence corn herbicides that will control grass weed species, including glyphosate, Liberty, and Lightning, require the use of herbicide-resistant/tolerant corn hybrids.--Aaron Hager and Christy Sprague

Author: Aaron Hager Christy Sprague


The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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