When applying contact herbicides, what is crucial for effective control?

For effective control when using contact herbicides, complete coverage of foliage is essential. Contact herbicides work by physically contacting and penetrating the plant tissues. By ensuring that every part of the target plant is adequately covered, the herbicide can effectively disrupt the plant's physiological processes, leading to its demise.

Complete coverage maximizes the chance that the herbicide will reach all the intended targets within the plant. If coverage is partial, there may be areas that do not come into contact with the herbicide, allowing those parts of the plant to survive and possibly regrow, thus diminishing the overall effectiveness of the treatment.

In contrast, partial coverage would leave parts of the plant untouched, providing buffering zones for regrowth, while application on windy days can lead to drift, which can reduce effective coverage on the target plant and potentially affect non-target plants. Mixing with a surfactant can enhance absorption and spread but is secondary to the necessity of achieving complete coverage for effective control.