Which temperature–humidity combination is unfavorable for application?

• A. Very low temperature and high humidity
• B. Very high temperature (85-90+) and low humidity
• C. Moderate temperature and moderate humidity
• D. Very low temperature and low humidity

Answer: (B)

When thinking about applying pesticides, how the air heats and dries directly changes how well the spray covers the target. Very hot conditions paired with dry air make spray droplets evaporate quickly and become finer. Those tiny droplets are prone to drifting off target and can land as insufficient amounts on the leaves, reducing efficacy and increasing the risk of off-target damage. Some products may also volatilize more in heat, causing more of the chemical to escape the intended area.

So that hot, dry combination is the least favorable for effective, safe application. In contrast, moderate temperatures with moderate humidity help droplets stay the right size and deposit more reliably, and very low temperatures with low or high humidity tend to pose fewer issues related to rapid evaporation and drift.