Which of the following factors contributes to herbicide failure?

Herbicide failure can be significantly influenced by environmental conditions and genetic resistance of weeds. Environmental conditions, such as temperature, humidity, and soil moisture, can affect the efficacy of herbicides. For example, extreme temperatures can degrade the herbicide before it effectively targets the weeds. Additionally, genetic resistance among weed populations has become increasingly common due to repeated exposure to the same herbicide classes. Weeds that have developed resistance can survive applications that would typically control them, leading to reduced effectiveness of the herbicide and contributing to failure.

In contrast, correct application timing, use of the highest recommended rate, and application during optimal weather conditions are practices that typically enhance the effectiveness of herbicides, rather than contributing to their failure. Properly timing the application ensures that the herbicide targets weeds during their most vulnerable growth stages. Applying herbicides at recommended rates helps avoid both underdosing, which leads to ineffective control, and overdosing, which can cause environmental damage or harm to non-target species. Finally, applying herbicides under optimal weather conditions (with respect to wind, rain, and temperature) maximizes the chances of effective weed control.