For years, MFA agronomists have promoted a planned two-pass system as the premier corn herbicide application program. However, many corn growers choose to go with a planned one-pass pre-plant or pre-emergent corn herbicide management program, and use rescue treatments if late-season weeds become a problem. Deciding whether to economically treat those fields is one of the toughest agronomy decisions that producers and crop advisers face annually.

If you are considering late-season weed control in corn, you need to evaluate weed species present, weed population, corn stand and yield potential, environmental factors, corn hybrid, corn growth stage, application capabilities and economics. Weed diagnostics can range from walking fields to a detailed analysis of weed competition, economic loss and herbicide selection using technology such as the "WeedSOFT" computer program recently co-released through the University of Missouri. Over the years, I have seen many problems with spot treating late-season cornfields. Unless dealing with a thick patch of isolated weeds, most late-season herbicide applications should be made on a whole field basis.

Please check the MFA Agronomy Guide or with your closest MFA Agri Services Center to get specific herbicide product, herbicide rate, surfactant requirement, tank mixes, tank mix compatibility or other advice concerning traditional late-season corn weed control options. Basically, you have six management options concerning rescue weed control options in corn. They are:

1. Use broadleaf herbicides
2. Use grass herbicides
3. Use both grass and broadleaf herbicides
4. Use specific herbicide for herbicide-resistant corn hybrid
5. Cultivation
6. Live with what you have

There are a few new herbicide options for late-season corn application. The following is a brief description of those products and their uses in corn. Please refer to product labels for complete recommendations of these products.

Callisto: This broadleaf herbicide was released last year from Syngenta. The recommended use rate is 3 ounces per acre. The active ingredient in Callisto is mesotrione, which is a triketone--pigment inhibitor compound. Callisto can be applied to corn up to 30 inches tall or the 8-leaf stage. Use a crop oil concentrate (COC) and nitrogen-based materials as spray additives with Callisto. Do not use a methylated seed oil (MSO) with this product. In test plots that I have observed, Callisto has worked very well on several annual broadleaf weeds, including tall waterhemp. Callisto is a good alternative to the growth regulator herbicides that are commonly used for late-season broadleaf weed control in corn.

Option: Option is predominately a grass herbicide from Aventis that has activity on some broadleaf weeds. The recommended use rate is 1.5 to 1.75 ounces per acre. The active ingredient in Option is foramsulfuron. Foramsulfuron is a sulfonylurea--amino acid inhibitor compound. Broadcast applications of Option are limited to emergence through the 5-leaf or 16-inch growth stage. Option is labeled for drop nozzle application onto corn between 16 and 36 inches in height. Option must be applied with an MSO in combination with a nitrogen fertilizer additive. Do not use non-ionic surfactants (NIS), COC or refined vegetable oils as spray additives with Option. Do not use Option if Counter, Thimet or Dyfonate insecticides have been used.

Steadfast: Steadfast is predominately a grass herbicide from DuPont that has activity on some broadleaf weeds. The recommended use rate is 0.75 ounces per acre. Steadfast is a combination of nicosulfuron and rimsulfuron, which are both sulfonylurea--amino acid inhibitor compounds. Nicosulfuron is the active ingredient in Accent. Rimsulfuron is an active ingredient contained in Accent Gold, Basis Gold and Basis. Steadfast was initially labeled for corn from emergence through the 12-leaf growth stage. That height requirement has now been increased to 20 inches or the 7-leaf stage. Use a COC or NIS plus a nitrogen material as spray additives with Steadfast.

Yukon: Yukon is a broadleaf herbicide product from Monsanto. The recommended use rate is 4 to 8 ounces per acre. Yukon is a combination of dicamba and halosulfuron. Dicamba is the active ingredient in Banvel and is a growth regulator herbicide. Halosulfuron is the active ingredient in Permit and is a sulfonylurea--amino acid inhibitor herbicide. It is questionable whether there is enough Permit in Yukon at the 4-ounce rate to effectively control nutsedge species. For yellow nutsedge control with Yukon, be sure to use 6 to 8 ounces per acre. Yukon should control most broadleaf weeds that dicamba and Permit are effective on.