Coolidge Weed Control
A herbicide is a chemical substance used to control or manipulate undesirable vegetation, especially weeds.
Herbicides are classified into two categories: selective and non-selective. Selective herbicides kill specific unwanted plants while leaving desirable vegetation relatively unharmed. Non-selective herbicides (total weed killers) kill all or most plant species.
Preemergence: used before crops or weeds emerge. May also refer to use after crops emerge or are established, but before weeds emerge.
Postemergence: used after the crop or weed have emerged.
Factors Affecting Herbicide Activity:
Rain during or closely following a foliar post emergence application may wash the herbicides from the leaves and reduce its effectiveness. Traces of rain do or precipitation from fog a few hours after spraying could increase penetration and Effectiveness by remoistening herbicidal deposits.
Rainfall is essential for satisfactory weed control from most pre-emergence herbicides. Rain moves the chemical into the top half inch layer of soil where most of the weed seeds germinate. The amount of rainfall required is about a half inch.
In general a high relative humidity at and after spraying is likely to increase herbicide oh penetration absorption and presumably the killing of the weed.
Post-emergent weed control is best when temperatures before spraying have favored uniform weed seed germination and rapid growth. At the time of spring high temperatures generally increase the activity of herbicides.
Some herbicides have limitations on surface applications when temperatures are warm.