Controlling Common Insect Pests and Other Ailments

Fortunately, citrus have few insect pests, and fungal problems are uncommon as well. Here are some tips for restoring your tree's health, should problems arise.
 
Pests, Ailments, & Beneficial Insects Slide Show
Having trouble identifying a problem with your citrus tree? Our slide show includes photos of the most common afflictions. Take a look.
 
Ants
Keep your tree free of ants. They will farm scales or aphids, moving them from place to place, milking their secretions, and protecting them from beneficial insects. Ant baits may be helpful.
 
Other Harmful Insects (Scales, Aphids, Mites, etc.)
If you find harmful insects like scales, aphids, or mites, a household spray bottle of water with some mild dish soap could be all you need. If insects persist, the usual nursery treatment is a 1% solution of light horticultural oil.
 
Choosing Insect Pest Treatments
Safer makes an aerosol product with Safer Soap and pyrethrins, a chrysanthemum derivative. Oils and soaps are available in nurseries or garden centers, or online at Peaceful Valley Farm Supply, a favorite of organic farmers. With any treatment you use, spray the underside of the leaves as well, following the manufacturer's recommendations. Do not use stronger solutions! Repeat as needed to treat insects newly emerging from eggs. It is not advisable to spray when it is above 90°F or below 40°F, or if it is windy.
 
Systemic Insecticides
Since trees have edible fruit, all insecticides should be used sparingly and carefully. DO NOT use systemic insecticides on citrus! They can travel through the plant and into the fruit.
 
Further Information
To learn more about garden pests and to see photos, visit the UC Statewide Integrated Pest Management Project at UC Davis.
 
Helpful Insects
Remember: not all insects are bad! Spiders, lady beetles, lacewings, and preying mantids (praying mantis) are some of the beneficial insects you may see around citrus trees outdoors. You can even buy some of these predator insects in local nurseries for release in your garden.
 
Sticky Foliage
Sticky substances are almost always the result of insect pests that can cover foliage with a clear sticky exudate. Sometimes a dark fungus can grow on the surface, giving some leaves a dark or black appearance. Additionally, sooty mold can develop on the sugary insect secretions in damp conditions.

The insects causing the residue can sometimes be difficult to see. They my be aphid, scale or leafhoppers. They may have left your plant, leaving the residue as evidence they were there.
 
To solve this problem, look on the underside of the leaves for small eggs or insects. Clean off any sticky spots on stem and leaves on small trees with a q-tip and rubbing alcohol. Outside, hose off the tree thoroughly with water. If insects are still present, spray the tree with a solution of horticultural oil or Safer's soap according to manufacturer's directions.
 
Sticky/Oozing Trunk
Older trees may be afflicted by brown rot gummosis at the base of the trunk, caused by a soil fungus called Phytopthera. You will notice a sticky substance coming out of the tree's trunk. Keep the base of the trunk dry; clear away any soil, mulch, grass, or weeds that might be holding moisture at the base; trim and clean any oozing wounds; and remove decayed bark to a point where no discoloration is visible. If water hits the trunk from sprinklers, that can trigger the fungus as well. Make sure water does not stand in a basin around the trunk during winter rains.
 
White Speckled Leaves
If the leaves on your tree are turning white, or are afflicted by white 'polka dots,' your tree may have spidermites. They are tiny, about the size of a period on a piece of paper. They may be red or white. When they feed leaves may appear speckled. They lay tiny eggs which may take a week or two to hatch, and they do spin webs. (Hence the name.)
 
To solve this problem, spray the tree with horticulture oil or miticide, both of which are available from your local nursery. Spray every 10 days for three weeks to kill newly hatching eggs. Consider washing tree off with water to eliminate dust from foliage every two weeks or so. Mites thrive in dust! Also, be sure to feed your trees every month with fertilizer that obtains trace elements.