Wet weather conditions across much of the state have slowed or halted fieldwork and contributed to crop stress in many areas. Once fieldwork can be resumed, many corn growers may be facing the scenario of whether to spray postemergence herbicides or wait until weather conditions and crop growth have improved.
There are several factors to consider before deciding when, and which postemergence herbicides to apply. Take into consideration that corn growing in very wet soils may be stressed and not able to metabolize herbicides as rapidly as it would under more favorable environmental conditions. Increased foliar burn may also occur with postemergence herbicides under these conditions. On the positive side, weeds should also be more susceptible to herbicide applications. If possible, it is best to wait until conditions improve but growers may not have this flexibility due to herbicide-crop stage or weed size restrictions.
There are a few guidelines to consider when deciding when and what to spray. Fields where the corn or weeds are approaching maximum size (according to label specifications) should be treated first. Double-check the label regarding any adjuvant recommendations. Often a spray adjuvant is necessary under droughty conditions, but under wet, humid conditions it would not be needed and may increase the potential for crop injury. Also, consult seed company guidelines for classification of hybrid sensitivity to herbicides. Some hybrids may be more sensitive to specific herbicide classes such as plant growth regulators or ALS inhibitor herbicides. If there is a noted interaction between an herbicide and a hybrid, ensure that the stage of corn is within the guidelines recommended and follow all other cautions or recommendations.
If adjustments or changes are made to an herbicide program, remember to consider the possible herbicide tank mix or insecticide interactions. Corn growing under stress will be less able to metabolize different combinations and thus may be more susceptible to injury. Review all relevant herbicide and insecticide labels and take into consideration any additional warnings or precautions.
This article originally appeared on page 53 of the IC-492 (9) -- May 31, 2004 issue.