Drought and Chemical Weed Control
Rakesh S. Chandran, Ph.D.
WVU Extension Service
This article was published in the July 1999.
How is the drought situation going to affect weed control? Most herbicides become less effective when a plant is under stress. Along with crops, most weeds are also experiencing water stress under current conditions. Therefore, you may have to wait until the soil is fairly moist before applying any systemic herbicides (e.g., Roundup) to manage weeds. Most systemic herbicides perform better under conditions that are ideal for weed growth. When the plants are free of stress, herbicides are absorbed faster and move better within the plant system, providing more efficient kill.
If herbicide application becomes inevitable, application of systemic herbicides early in the morning may be more effective. Spray additives or adjuvants may enhance herbicidal effectiveness based on label recommendations. Another option would be the use of contact herbicides (e.g., Gramaxone Extra). However, it should be noted that the higher daytime temperatures (>90F) may cause injury to crops from contact herbicides. Therefore use of a lower rate, if the label permits, is advisable under such conditions. REMEMBER? always read the LABEL!
I am compiling a comprehensive list of herbicides that you may have applied in the spring, along with the wait periods for crops that may be planted this fall. Contact me for additional information.