Which of the following factors does NOT affect the uniform application when using a backpack sprayer?

When using a backpack sprayer, uniform application relies heavily on several operational factors. Weather conditions, while certainly relevant to overall spraying effectiveness and safety, do not directly influence the precision of how the pesticide is applied from the sprayer.

Uniformity in application comes from controllable aspects such as walking speed, nozzle height, and nozzle angle. Walking speed affects the rate at which the pesticide is applied; if the applicator walks too fast, the amount applied per area will be less than intended. Nozzle height influences how far the spray travels and how evenly it spreads across the target area; if the nozzle is too low or too high, it may not deliver the product uniformly. Similarly, nozzle angle impacts the direction and pattern of the spray, which is crucial for achieving even coverage.

In contrast, while weather conditions, such as wind, humidity, and temperature, can affect how the spray behaves once it leaves the nozzle, they do not change the uniformity of the application itself. Therefore, among the given options, weather conditions are less about the mechanics of application uniformity and more about external factors that can influence the overall effectiveness of the pesticide application.