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Issue No. 5, Article 10/April 23, 2004

Dry Soils and Soil-Applied Herbicides

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
1/2 to 1 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 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 4leaf (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 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 89.46WDG (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 are listed on the label. Applications of Basis Gold must include a COC (petroleum or vegetable based) or an NIS. An ammonium nitrogen fertilizer must be included with the COC or NIS. Basis Gold may be applied to corn up to 12 inches in height or exhibiting up to six leaf collars. Do not apply to corn taller than 12 inches or exhibiting more than 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 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; quackgrass up to 8 inches in height; and 8- to 12-inch-tall johnsongrass. Apply Steadfast to corn up to 20 inches tall or exhibiting up to six leaf collars, whichever is more restrictive. Applications must include a COC or an 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. Grass species controlled by Steadfast ATZ (nicosulfuron + rimsulfuron + atrazine) are similar to those listed on the Steadfast label. However, Steadfast ATZ can be applied to corn only up to 12 inches in height or that is exhibiting up to six leaf collars.

Option 35WDG (foramsulfuron) can be applied broadcast at 1.5 to 1.75 ounces per acre when corn is in the V1 through V6 growth stages. Methylated seed oil in combination with nitrogen fertilizer is the preferred additive system. Option controls many annual (generally 2- to 8-inch-height range) and some perennial grass species. The label contains precautionary statements regarding the use of Option on corn previously treated with certain insecticides. The label of Equip 32WDG (foramsulfuron + iodosulfuron) lists many of the same grass species as the Option label, but grass heights are generally reduced.

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 an 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 postemergence 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

Author:
Aaron Hager

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