TheBakersfieldCalifornian.com

A new exotic pest of citrus, citrus leaf miner, is spoiling the natural beauty of citrus foliage in the southern San Joaquin Valley.

The global pest, first found in California in Imperial County in 2000, has now moved up the coast and inland to sites throughout Kern County. Adult moths lay eggs that hatch into small worms that feed and cause mines in citrus leaves. In the summer and fall, when citrus trees begin to put out new growth, the new leaves become completely distorted, stunted and misshapen.

For most, citrus leaf miners will likely be nothing more than a nuisance. Research has shown that mature trees can tolerate damage without affecting the number or size of fruit. However, damage from feeding by the leaf miner can severely stunt young trees, and can reduce the aesthetic quality of citrus trees used for landscaping.

In most cases, control is not needed. Where the homeowner feels that it is, control can be difficult to achieve with foliar sprays because larvae are protected within the leaf from beneficial insects or pesticides.

Some assistance can be achieved by keeping new leaf growth to a minimum by removing sucker growth at the base of the tree and by not over-pruning or over-fertilizing. For bearing and non-bearing trees, homeowners can use imidacloprid (Bayer Advanced Fruit, Citrus, Vegetable Insect Control concentrate) to help alleviate the problem. This is a systemic pesticide that can be used once during the season. Read and follow label directions closely.

Generally, because lemons and grapefruit tend to produce many new leaves early in the spring and throughout summer and fall, these varieties often show the earliest and some of the worst symptoms.

Treating lemons and grapefruit with imidacloprid may be advisable in late May or early June, whereas postponing treatment of navel oranges until July may help extend the effective life of this insecticide.

Infestations of citrus leaf miner peak in August, September and October. Citrus leaf miner is not active during the winter, and treating this pest during the winter, early spring or during bloom will not be effective.

It is also important not to confuse citrus leaf miner with citrus peel miner. Citrus peel miner is another new pest found on the fruit and stems of citrus and other landscape plants. Citrus leaf miner, on the other hand, feeds almost exclusively on the leaves of citrus.

Both pests produce mines that cause primarily cosmetic and superficial damage.

In other countries, the two pests are attacked by several parasitic wasps that are barely visible to the naked eye. Efforts are under way to import more of these natural enemies to California. Once here, the hope is that these insects will become established and spread throughout urban and agricultural sites to feed on and control these pests.

For the meantime, it is important to learn to tolerate less than beautiful citrus trees until a long-term solution can be achieved.

More information on citrus leaf miner and its control can be found at the University of California Integrated Pest Management website at ipm.ucdavis.edu/PMG/PESTNOTES/pn74137.html.

David Haviland and Craig Kallsen are both farm advisers for the UC extension, the former in entomology and pest management and the latter in citrus, subtropical horticulture and pistachios.