- Dew forms when plant surfaces cool below the dewpoint, causing water to condense on leaves overnight.
- Dew can cause spray to either run off or become diluted, raising concerns about morning herbicide effectiveness.
- Experiments show large spray droplets are likelier to run off dew-saturated plants than smaller droplets.
- Despite runoff differences, some studies found overall spray efficacy was not affected by droplet size.
- Consider weed type, surfactants, and dew conditions when deciding whether to spray through dew.
This text was generated by OpenAI GPT 5 Mini
When warm air is cooled, it loses some of its moisture-holding capabilities. This change often occurs at night, when plants (and other objects) cool. Once the temperature of the surface of the leaves, for example, drops below the dewpoint, it causes water to condense, forming the shiny dew that causes so many to question early morning spray applications.
The question is often: will the spray run off the plant or will it get so diluted that it doesn’t work anymore?
In a dew chamber, work has shown that large spray droplets are more likely to run off a plant saturated with dew than their smaller counterparts. However, similar work showed that spray efficacy was not altered by droplet size.
Wolf discusses this work and the potential answer to the seemingly conflicting findings. Wolf also explains how grassy weeds compare to broadleaves, the role of surfactants, and what to consider when making the decision to spray through dew or not.
