Weed Killer – Temperature Affecting Ability to Apply

Q: Enlighten me regarding the preferred temperature to apply weed killer to lawn grass. The label says it should not be applied if the temperature is 90 degrees or greater. Can it be applied in the morning, before the temperature rises?

A: An excellent question! The reason for the temperature warning is that plants cells are growing rapidly in the heat and thus are more likely to be affected by chemicals. General grass health and stress also determine if a weed killer will cause damage. Applying in the morning, when it’s going to be hot soon, is not a good idea. Better to spray the chemical in the evening, when temperatures are falling.