It is not recommended to spray fungicides when there is dew.
Based on the authoritative information in the search results, spraying fungicides when there is dew will significantly reduce the efficacy of the drug and even increase the risk of drug damage. The following are specific reasons and scientific suggestions:
1. Dew dilutes the concentration of the drug solution
Dew will mix with the fungicide, resulting in a reduction in the effective ingredients actually attached to the crop, reducing the control effect. For example:
Liquid formulations will be diluted twice by dew, and the concentration will be inaccurate;
Powders may form local high-concentration areas due to dew, causing drug damage.
2. Affecting leaf absorption
The wet leaf surface will hinder the penetration and absorption of fungicides:
The stomata are closed or slightly closed under low temperature and humid conditions, making it difficult for the drug solution to enter the plant body;
Dew may cause the drug solution to slide off the leaves, reducing the amount of attachment.
3. Best spraying time recommendation
To avoid the influence of dew, fungicide spraying should be selected:
Sunny and windless weather, between 10 am and 4 pm (leaves are dry and stomata are open);
Avoid high temperatures at noon in summer (the liquid medicine is easy to evaporate).
Exceptions: Herbicides may be more effective due to the extended residence time of dew (different from the mechanism of fungicides), but fungicides still need to strictly follow dry conditions.
