A few hours can make all the difference in the world when applying the new cotton herbicide Staple on pigweed, according to a pair of Texas researchers.

James R. Mahan, a USDA-ARS plant physiologist and Peter Dotray, a weed scientist at Texas Tech and Texas A&M universities in Lubbock found that when the herbicide Staple applied on pigweed in the afternoon when temperatures are above 93 degrees, pigweed was barely affected. Just six feet away pigweed sprayed in the cooler morning was almost totally killed.

Staple works by inhibiting a key plant enzyme. According to the scientists, the plant is most vulnerable to Staple in the temperature range of 68 to 93 degrees. Two years of field studies confirmed lab results.

Mahan and Dotray recommend that farmers check the five-day forecast before they schedule a Staple application to see which days will be the coolest. They suggest farmers stop spraying when the day gets too warm. Even though Staple takes two weeks to kill weeds, the temperature at spraying time has the greatest effect on how well the over-the-top herbicide works.