Be careful of nozzle positioning, especially on mornings with heavy dew. The upright leaf corn hybrids can create a funnel effect for spray, and dews can create a major run-in effect from spraying (droplets become "big drops," turning to droops).|
2,4-D requires drop nozzles for corn over 8 inches tall. 2,4-D low volatile (LV) esters will volatilize. Use amine formulations when temperatures approach 80°F to 85°F. Shotgun and Scorpion III contain 2,4-D and so also require drop nozzles at the 8-inch stage, but other components have different maximum corn size limits; for example, Shotgun has a 12-inch limit (atrazine) and Scorpion III has a 24-inch limit (Stinger). Hornet also contains Stinger, but limits are 20 inches for corn or V-6 stage.
Atrazine must be applied before corn is 12 inches tall. Accent Gold, Buctril + atrazine, Contour, Extrazine, Laddok, Liberty ATZ, and Shotgun contain atrazine and so have the same 12-inch limit. Marksman contains atrazine, but the size limit is 8-inch or 5-leaf corn (dicamba rate break).
Dicamba (Banvel, Clarity, Celebrity B; in Marksman and NorthStar): The rate for Banvel/Clarity (dicamba) is lower on corn over 8 inches tall or 5-leaf, but these two herbicides can be applied to corn up to 36 inches tall. If soybeans are over 10 inches tall or have begun to bloom, the limit is 24-inch corn to minimize drift potential. This warning also applies to Celebrity B (dicamba) and NorthStar (dicamba + prosulfuron; see below). Distinct (dicamba + diflufenzopyr) limits are 6 oz/A on 4- to 10-inch corn and 4 oz/A on 10- to 24-inch corn.
Prosulfuron (Exceed, Spirit, and NorthStar) can be applied from 4-inch up to 20-inch corn. Drop nozzles allow later application; Exceed can be applied at up to 30 inches, and Spirit up to 24 inches or V-6 stage. Northstar (dicamba + prosulfuron) can be applied (1) over the top from 4 inches to 20 inches or V-6 stage, and (2) with drop nozzles for up to 36-inch corn (dicamba limit). Note the warning about dicamba in the previous paragraph.
Some corn herbicides have V-6 to V-8 limits (this is the number of leaves showing leaf collars, not the number of pistons in a car engine). Accent requires drop nozzles after the 20-inch or V-6 stage up to 36 inches or V-10. Celebrity limits are V-6 or 20-inch corn. Roundup Ultra limits on RR-corn are 30 inches or V-8 stage. Liberty limits on LL or GR corn require drop nozzles at the 24-inch or V-7 stage up to 36-inch corn.
IMI corn allows imazethapyr (Pursuit) use on corn. The IMI corn herbicides are Contour, Resolve, Lightning, and Pursuit. Contour, Resolve, and Pursuit are to be applied before corn is 12 inches tall. Lightning has weed size limits, but no corn size limits, on the label.
Poast Plus on PP corn and Buctril (field corn) can be applied up to tassel stage, whereas Permit can be applied up to "layby" (cannot cultivate anymore). Resource can be applied to corn from the 2-inch stage up to V-10 stage.
Table 1 contains information about postemergence corn herbicides with respect to adjuvants, preharvest intervals, and maximum corn size for application.--Marshal McGlamery