If I apply a herbicide early in the morning when the temperature is below 70 degrees and the dew is still on the weeds, will it still be effective when the temps rise to 90 degrees in the afternoon? By that time, the chemical has been absorbed into the plant, but I'm wondering if our high temperatures will slow down the work of the herbicide. Specifically, I want to use a poison ivy/brush killer that is rated for use on trumpet vine. I would hate to have to wait until the weather cools to get at the huge patch of this stuff. The plants are still less than a foot high and would be easier to kill now than later.