Too Hot to Spray?
Herbicide leaf applications on noxious brush and weeds are in full swing across the state. I often get asked when the cut-off time for spraying would be…which is of course going to vary from South to North Texas. However, it is a bit confusing when to stop leaf sprays when it is still warm enough for the plant to actively grow.
Hot conditions can impact the injury to plants by herbicides because plants develop a thicker wax layer on the leaf surface to reduce moisture loss. This barrier can keep herbicide from effectively entering the leaf. Also, the plant may slow down their rate of translocation and metabolism when it is really hot, decreasing the amount of chemical that is taken down to the roots to kill the plant.
So what is that cut-off date? Hard to say – but usually individual plant leaf treatments are more effective for longer into the summer than broadcast treatments. Once we get into the July heat down in South Texas, leaf applications are typically stopped, and more time is spent on stem and cut-stump applications.
Finally, keep in mind that ester formulations of herbicides can increase volatilizing when it’s really hot – so you may not want to use them near or under desirable trees when conditions are harsh.