Foliar sprays are most effective when?

• A. Midday under bright sun.
• B. Any time regardless of stomata.
• C. Night when temperatures are lowest.
• D. Early morning or late evening when stomates are open.

Answer: (D)

Foliar sprays work best when the leaf’s stomata are open, so the spray can enter the leaf tissue efficiently. Stomata are the tiny pores on the leaf surface that regulate gas exchange and water loss. Early morning or late evening are ideal because temperatures are cooler and humidity is higher, sometimes with dew still present, which helps the leaf stay moist long enough for the spray to be absorbed. When conditions are hot and bright during the day, stomata tend to close to reduce water loss, and droplets can evaporate quickly or cause leaf burn, making absorption less effective. At night, stomata are usually closed too, so uptake is limited. In short, opening stomata and favorable moisture/temperature conditions in the early or late parts of the day maximize absorption of the spray.