What is required for effective control of weeds by contact pesticides?

For effective control of weeds using contact pesticides, complete coverage is essential. Contact pesticides work by physically adhering to the plant surface and disrupting cellular processes upon contact. If the pesticide does not cover the entire plant, particularly the leaf surfaces where photosynthesis and other vital functions occur, then it cannot effectively penetrate and damage these critical areas. This lack of coverage can lead to incomplete control of the weed, allowing it to survive, regrow, or spread.

Achieving complete coverage ensures that the active ingredients in the pesticide have maximum opportunity to interact with the target plant's tissues, leading to optimal efficacy. This is especially important for contact herbicides as they do not translocate within the plant; hence, any untreated areas will remain unaffected.

Moisture retention, high temperatures, and frequent applications can play roles in overall plant health and pesticide performance, but they do not directly relate to the effective control of weeds by contact pesticides in the way that complete coverage does.