If you've been noticing tiny white insects fluttering up from your plants when you brush against the leaves, you're not alone. Whiteflies are one of the most common complaints we hear this time of year. The good news is that they can be managed with some straightforward strategies.
Whiteflies can be a real nuisance, but before reaching for the pesticide sprayer, try the simplest remedy first: a strong spray of water from your hose. Hosing down the leaves does double duty. It knocks whiteflies off the plant and reduces the hot, dusty conditions they love, while giving their natural enemies a better chance to do their work.
Yellow sticky traps are useful for monitoring whitefly activity—they can give you a sense of how bad the problem is—but they're not very effective for control. They also have a downside: they often trap beneficial insects, including the natural enemies that help keep whitefly populations in check.
If you need to treat, look to the least-toxic options first. Insecticidal soaps and horticultural oils (including Neem oil) are effective, but they will only control whiteflies that are directly contacted by the spray. That means thorough coverage is essential, especially the undersides of leaves which is where whiteflies tend to congregate, often on the lower portions of the plant. One important caution: don't apply oils when temperatures are expected to exceed 90°F, as this can damage plants.
One often-overlooked clue in managing whiteflies is ants. Ants actively protect whiteflies (and other soft-bodied pests like aphids and scale) from their natural enemies in exchange for the honeydew those pests produce. On citrus trees especially, ant management can make a significant difference. See the links below for guidance.
Finally, preserve natural enemies and whitefly parasites by avoiding general pesticide use in your yard. Several predators, including lacewings and their larvae, prey on all stages of whiteflies.
More Information
• Managing whiteflies: https://ipm.ucanr.edu/home-and-landscape/whiteflies/#gsc.tab=0
• Ant management in gardens and landscapes: https://ipm.ucanr.edu/home-and-landscape/ant-management-in-gardens-and-landscapes/#gsc.tab=0
Help Desk of UC Master Gardeners of Contra Costa County (RDH)