Citrus solutions

May/June 2008

Advice for your quest against citrus pests

By David Ross

So often we take our citrus trees for granted, not bothering to care for them as long as we get fruit. But citrus trees seem to be bug magnets, attracting pests that weaken our trees, cover them with a black substance we often blame on automobiles and jets, and decrease the quality and quantity of our harvest.

The most common invaders are aphids, scale, mealybugs and leafminer.

Aphids usually arrive on tender, new growth in the spring. They begin sucking on the leaves and cause uneven damage, which will make the leaves curl and contort around the damage. Aphids, like people, come in many shapes and sizes – many colors, too, including green, yellow, burgundy and black.

Scales are round or oblong shelled creatures that cover mature leaves and stems. They, too, suck energy from the plants.

Mealybugs are cottony critters that invade nooks and crannies, fill the navels of oranges and hide between the fruit in clusters.

All these pests sap energy from your trees and excrete a sugary substance called honeydew. This honeydew attracts ants that "farm" your pests, moving them around your trees and fending off the beneficial insects. A black fungus called sooty mold grows on the honeydew, creating a mess that is commonly blamed on cars and jets.

All the above can be easily controlled. Your first line of defense should be water. Hose down your trees at least once a week during summer.

In the spring use horticultural oil to smother existing pests and prevent their getting a foothold. I use Summit Year-Round Spray Oil. This paraffinic oil kills a wide variety of pests by smothering them and is safe to use on edibles. As with any pesticide, read and follow the label directions carefully so you end up killing your pests, not your trees.

Leafminer is a relatively new pest in California. It invades new foliage in late spring, tunnels its way just under the cuticle of the leaf in a zigzag pattern, then tucks itself under a leaf corner to pupate.

The paraffinic oil can deter the parent moth, which lays the leafminer egg. But also consider spinosad, which will control citrus leafminer and can be used up to six times per year.

Make sure to feed and water your trees regularly. A vigorous, healthy tree is less susceptible to insects and gives a better harvest. Good luck!

David Ross is a horticulturalist and manager for Walter Andersen Nursery in San Diego and Poway.