If rain occurs a few hours after applying a postemergence herbicide that is absorbed slowly, what could happen?

If rain occurs a few hours after applying a postemergence herbicide that is absorbed slowly, what could happen?

• A. It may increase absorption
• B. It could wash the chemical off foliage before absorption
• C. It could cause rapid translocation within the plant
• D. It would have no effect

Answer: (B)

Rain a few hours after applying a slow-absorbing postemergence herbicide can wash the chemical off the leaf surface before it has a chance to enter the plant. These products need time on the foliage to penetrate into leaf tissues; if rain comes soon after application, the surface concentration is removed, leaving little herbicide to be absorbed and reducing control. Translocation into the plant isn’t instant and isn’t accelerated by rain, especially with slow-absorbing formulations. On the other hand, a rain event after application wouldn’t be expected to produce stronger effects, and in fact can lead to poor performance or the need to reapply.

Rain a few hours after applying a slow-absorbing postemergence herbicide can wash the chemical off the leaf surface before it has a chance to enter the plant. These products need time on the foliage to penetrate into leaf tissues; if rain comes soon after application, the surface concentration is removed, leaving little herbicide to be absorbed and reducing control. Translocation into the plant isn’t instant and isn’t accelerated by rain, especially with slow-absorbing formulations. On the other hand, a rain event after application wouldn’t be expected to produce stronger effects, and in fact can lead to poor performance or the need to reapply.