California red scale on Imperial Valley citrus

April 29, 2002|By Eric T. Natwick, Imperial County-University of California Cooperative Extension adviser

California red scale, Aonidiella aurantii (Mask.), is one of the most damaging insect pests of home citrus orchards in the Imperial Valley.

This insect attacks all parts of the trees, including fruit, leaves, twigs, branches and trunks. Large numbers of scales can give the fruit and leaves an unsightly appearance, can cause leaves and fruit drop and can kill small branches.

Cultural controls can help prevent infestations. The movement of red scale by wind or birds cannot be easily prevented, but scale movement can be prevented by cleaning boxes, ladders, bags and other picking equipment after working in infested trees and before moving on to work in non-infested trees. Clothing should also be well brushed to prevent the spread of crawlers.

Detect and control early: Inspect your trees on a regular basis at frequent intervals to detect any red scale infestation that may be starting. If an infestation is detected early enough, the branch or branches with infestation can be pruned from the tree. Stripping infested fruit from trees can help reduce the scale population growth. This practice is helpful prior to spraying the tree with an insecticide.


Insecticides are needed to successfully control or eradicate red scale from a citrus tree. Timing of insecticide applications is important. The female red scale produces a pheromone (sex attractant) to lure males for the purpose of mating. Prior to mating, the female scales are loosely attached to the citrus tree and are susceptible to insecticide sprays. Therefore, spray applications should be made before most of the females have mated and cemented themselves to the citrus plant. The easiest way to time insecticide applications is to monitor the male red scale flights using sticky traps, which contain pheromone attractant. The insecticides should be applied beginning immediately at peak emergence of a male flight during the spring or fall.

The preferred timing is during the period immediately following petal fall during a peak male flight but before fruit becomes infested, which generally occurs in July. If you don't have pheromone traps, then the best time to spray is during the natural fruit thinning between mid-April and mid-May. To avoid harming honeybees, don't spray insecticides during bloom.

The insecticides of choice for red scale control by homeowners include malathion, diazinon and carbaryl. Insecticidal control of red scale requires the thorough application of the proper insecticides to all parts of the tree.

The home orchard may be treated using a garden hose with a good quality hose end spray nozzle attachment. Homeowners should wear protective equipment such as rubber gloves and boots when applying these insecticides to their trees as well as tight fitting protective goggles, waterproof hat, coveralls and a protective charcoal filter spray mask. All these materials should be properly disposed of or cleaned after spraying.

When spraying for red scale, spray the inside of the tree's canopy on one side first, standing on the opposite side of the canopy. Let the insecticide spray dry. When dry, enter the canopy on the sprayed side and spray the opposite side. After the inside of the tree's canopy is sprayed, spray the outside of the tree. Soak all foliage, branches and trunk of the tree. Read and follow all label directions with special attention upon safety equipment and storage.

A third weapon to combat California red scale is the release of Aphytis spp. parasites. Control has been achieved in California orchards using tiny parasitic wasps that only sting scale insects. Conditions necessary to achieve effective control with red scale parasites include favorable weather, ant control, a minimum amount of dust and avoidance of insecticides that may harm the parasite population. Weather conditions are most favorable in coastal and inland areas, excluding the southern deserts.

In desert areas such as the Imperial Valley, it is difficult to establish the Aphytis spp. parasites due to adverse weather conditions, especially when temperatures exceed 100 degrees during the summer. For control of red scale in our area, releases should be made during the spring of fall when many female scale insects have not mated and the temperatures are cooler.

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