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Problem Solver: Pests and Ailments - 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. Commercial ant baits that contain boric acid or arsenical poisons can be helpful.  Natural concoctions made at home can also work.  You can make an insecticide spray that will also repel ants.    

Other Harmful Insects (Scales, Aphids, Mites, etc.)
If you find harmful insects like scales, whitefly, aphids, or mites, a household spray bottle of water with some mild dish soap could be all you need. Use a soft toothbrush to scrub off scales if necessary.  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 pyrethrin (a chrysanthemum derivative). Oils and soaps are available in nurseries or garden centers, or online at Peaceful Valley Farm Supply. 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
Particularly on plants that produce edible fruit, it is important to use all insecticides cautiously and sparingly.  Try to avoid systemic insecticides, since they are moved throughout the plant, and residues may occur in the fruit.
 
Sticky Foliage
Sticky substances are often the result of insect pests in the order Homoptera that excrete a sweet sticky substance called “honeydew.” Commonly, a secondary invader, a fungus called sooty mold, will colonize the honeydew exudates, giving affected leaves a blackish appearance.  The insects causing the residues (usually aphids, whiteflies and scales) can sometimes be difficult to see, and the residues may remain after the pests have left the scene.  Affected areas can be cleaned of with mild soapy water.
 
To monitor for pests, look on the underside of the leaves, on stems and in notches of branches.  A hand lens can be helpful.  A cotton swab moistened with rubbing alcohol or a soapy solution can be effective for cleaning off pests and sticky residues. Outside, hose off the tree thoroughly with water. If insects are still present, spray the tree with a solution of light horticultural oil or Safer soap according to manufacturer's directions.  A soft toothbrush or thumbnail can help in dislodging scale insects.
 
Sticky/Oozing Trunk
Older trees may be afflicted by brown rot gummosis at the base of the trunk, caused by a soil fungus called Phytophthera. Typically, you will notice a sticky substance coming out of the tree's trunk. Weed eater and rodent damage can lead to gummy bark secretions.  Keep the base of the trunk dry, and clear away any soil, mulch, grass, or weeds that might be holding moisture at the base.  Trim away infected areas with a sharp (clean) knife, use tree seal to cover the wound and monitor for recurrence.  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 or after irrigating.   Be sure to always clean pruners with alcohol or another antiseptic cleaner between uses to prevent disease spread among trees.
 
White Speckled Leaves
If the leaves on your tree are turning white, or if you see white 'polka dots,' your tree may have spider mites. They are very tiny, and difficult to see without a hand lens. They may be red or white. Spider mites suck the juices from leaf cells, causing leaves to bleach out.  Spider mites can be controlled with soap and oil sprays, if the problem is discovered early.  A very effective product for spider mite and other sucking insect control is Organic Orange TKO.  This multi-purpose organic cleaner, used at the most dilute rate, will knock down mites and kill eggs.  Be sure to monitor weekly to be ready for any pest recurrence.  You may need to spray about every 10 days for three weeks to kill newly hatching eggs.  Predaceous mites and many other beneficial organisms can be purchased.  One reputable source for beneficial organisms is ARBICO.

Mite pests commonly appear on plants that are stressed.  Stress factors for outdoor trees include excessive road dust.  Mites thrive in dust! If possible, every two weeks or so, wash the dust off of tree foliage. Also, to keep trees healthy and stress free, be sure to feed your trees regularly, according to directions, with a good high nitrogen citrus fertilizer containing trace elements.

Helpful Insects
Spiders, lady beetles, lacewings, and preying mantids are some of the beneficials you may see around citrus trees outdoors. You can sometimes buy beneficial organisms, such as lady beetles, at local nurseries, or check out ARBICO at the link above. 

Further Information
Strive to utilize the least toxic pest management options at all times!  Integrated Pest Management is a sensible approach.  To learn more about IPM, including help identifying pests and beneficials, visit the UC Statewide Integrated Pest Management Project.

Find more information under our Helpful Links.