AUBURN, Ala.— Low temperatures stretching into March and April, with more potentially on the way, may cause issues for producers during burndown.
During March and April, producers normally apply burndown herbicides to prepare to plant corn, soybeans and cotton.
Dr. Joyce Tredaway, an Alabama Extension weed specialist, said this is not new for Alabama producers, as temperatures are often in the 70s during the day and the 30s at night.
“Many growers are concerned about temperatures affecting their burndown herbicides with cool days and near-freezing nights,” Tredaway said.
The statement found on most post-emergence herbicide labels is to apply when “weeds are actively growing.”
However, freezing or very cold temperatures do not kill the plant but plants will take time to begin actively growing again.
“Herbicides applied immediately after a frost may show reduced performance,” she said. “Watching the plants is the best way to determine if the plants have recovered and are ready for a burndown treatment.”
Any herbicide that translocates or moves within the plant will slow down tremendously during cool temperatures. Glyphosate is a translocating herbicide.
“The general recommendation is to avoid applying glyphosate when nighttime temperatures fall below 40 degrees Fahrenheit,” Tredaway said. “Herbicides, such as dicamba and 2, 4-D work better than others during times with cooler temperatures.”
Cooler weather will not have adverse effects on light-activated herbicides such as Sharpen, atrazine and Gramoxone. However, these herbicides would work more consistently if nighttime temperatures were warmer (50s). Tredaway said this is because the herbicides interfere with photosynthesis. Burndown herbicide effectiveness depends on the amount of sunlight on application day and the following days.
Herbicides Affected by Weather
Weather conditions, including temperature, have directly affect herbicide applications.
“Herbicide labels advise on the proper temperatures to apply in order to get a consistent kill of the target weeds,” Tredaway said.
Clouds, fog, cool weather or drought can add to the stress of a plant affected by temperature. During an Alabama spring, producers often experience low nighttime temperatures followed by higher daytime temperatures. Producers should anticipate slower activity and potentially inconsistent control, depending on the product used.
“Sometimes increasing the herbicide rate or spray additives can enhance performance,” Tredaway said. “Always read the label and stay within the label rates.”
Alabama Extension recently released a timely information sheet written by Dr. Tredaway, which you can find here. For more information, contact your local Extension office or reach out to local crops agents.