If you have citrus trees, you likely have citrus mealybugs
Citrus mealybug description
All mealybugs are soft, flat, oval-shaped critters with segmented bodies. The mealybugs that attack Morgan Hill citrus are covered with a white wax that also creates spines (filaments) around the outer edge and the back end of the bug. Unless you use a hand lens you probably won't notice individuals, but mealybugs colonize areas creating white, fuzzy egg clusters that are easy to spot.
When mealybug eggs hatch the crawlers are pale yellow with red eyes, and distinct antennae. Crawlers are not born with their protective wax coating. They begin to excrete it soon after hatching. They are called crawlers because they crawl to a feeding site, where they will continue to develop (and damage fruit) for a month or two.
Citrus mealybug damage
Each female mealybug can lay hundreds of eggs, and there are usually two or three generations a year, so infestations can become a problem. As sapsuckers, citrus mealybugs pierce fruit, leaves, and young stems to get at the sap. They also feed on tender, new growth. As they feed mealybugs leave behind a trail of honeydew that attracts ants and creates the perfect growth medium for sooty mold. Citrus mealybug feeding near fruit stems also leads to fruit drop. This feeding also reduces fruit quality. Trees fail to thrive and are prone to infestation by disease and other pests. In addition to oranges, lemons, limes, and grapefruit, citrus mealybugs also have a taste for ornamental plants, such as tulips, coleus, cyclamen, begonias, and dahlias.
How to control citrus mealybugs
The first step to controlling citrus mealybugs is to monitor your trees, especially in spring and fall, for signs of ant trails, sooty mold, and egg clusters. Since ants will protect and farm the aphids for their honeydew, apply sticky barriers to tree trunks to block ants from protecting the aphids against natural predators. Those natural predators are your trees' best defense against citrus mealybugs. Lady beetles, lacewings and hoverflies will devour these pests so avoid using broad-spectrum pesticides. For extreme infestations, you can buy an introduced predator called the mealybug destroyer (Cryptolaemus montrouzieri). Insecticides are not recommended. Diatomaceous earth and insecticidal soaps can also be used.
Mealybugs prefer dusty conditions so hosing trees off can make them less appealing to citrus mealybugs.
by UC Master Gardener Kate Russell
This article first appeared in the March 23, 2018 issue of the South Valley Magazine.