Early season corn. (Photo: D. Lingenfelter)
The unusual weather patterns interspersed with recent rainy and windy periods have made it difficult for timely herbicide applications. In some cases, burndown herbicides and residuals were applied a few weeks ago and are now running out of steam or the corn is already coming up and no herbicides including a burndown have been applied. Unless it’s Roundup Ready or Liberty Link corn, the options for broadspectrum burndown are very limited. (We do not recommend application of Gramoxone even if the corn is in spike stage, but would suggest other herbicide tank mixes or using 2-pass herbicide programs.)
There are a number of herbicides, including residual products that can be applied after planting up until corn and weeds reach a certain size or growth stage. The greatest risk of failure comes with trying to control annual grasses such as foxtail and panicum as they are emerging without including a foliar applied herbicide. With the increasing acres of Roundup Ready (glyphosate) and Liberty Link (Liberty 280) corn, we have more flexibility in how we manage weeds after emergence.
In addition, a number of “conventional corn” products are available to control emerged grasses (e.g., Accent Q, Basis Blend, Capreno, Impact/Armezon, Realm Q, Resolve Q, Steadfast Q) and even more are available for broadleaf weed control. In most cases, these POST or foliar-applied herbicides can be tank-mixed with residual products to provide several weeks of control. For most products, do not apply in a liquid fertilizer carrier if corn has emerged or injury may occur. Maximum corn and weed sizes vary for early POST herbicide applications in corn depending on the product.
Princep, Prequel, and Verdict must be applied before corn emergence. Balance Flexx and Corvus contain a safener and can be applied up to early POST (V2 growth stage) to corn. Zidua products and Instigate can be applied early post. Other herbicides such as Bicep II Magnum, Dual II Magnum, etc. can be applied to corn up to 5 inches tall. Acetochlor-containing products such as Degree (Xtra), Harness (Xtra), FulTime NXT, Keystone (LA) NXT, Resicore, and SureStart II can be applied to corn up to 11 inches tall. Herbicides including Atrazine, Acuron, Lumax, Lexar, Guardsman Max, and Realm Q can be applied to corn up to 12 inches tall (20 inches tall for Resolve Q and Python). And finally, Acuron Flexi, Prowl H2O, Halex GT, and Warrant can be applied to 30 inch tall corn or less.
Keep in mind, when tank-mixing with other pesticides follow the most restrictive product label. For a listing of additional herbicides and maximum corn heights and information on maximum weeds sizes for these products please refer to Table 2-10 in the Mid-Atlantic Field Crop Weed Management Guide . Or refer to the most recent herbicide label for use guidelines and additional information—CDMS Applied Intelligence or Greenbook Data Solutions or Agrian.