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Ask Your PCA: How can farmers manage spider mites and scale in citrus?

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Issue Date: September 9, 2020
Chris Boisseranc PCA, Southwest Ag Consulting Inc., Redlands
Chris Boisseranc

Spider mites and scale are the predominant pests in citrus, so it's important to ensure they aren't at economic levels as fall arrives.

Spider mites feed on the canopy and fruit. They have a fast reproductive rate. New immatures and adults will do extensive feeding, and they can quickly desiccate the tree and cause blasting (defoliation of the tree). Heavy defoliation leads to less production the next season, and it will take several years for the trees to recover.

Spider mites damage the fruit as well, with heavy stippling. The stippling leaves a light-colored spot on the fruit, and if the damage is heavy enough to bleach out the coloring of the fruit, it will be marked down as a second.

Dust boosts the spider mite's metabolism. They create more eggs and their numbers will increase in dusty conditions, so dust control is important to managing spider mites.

There are a handful of conventional pesticides used for spider mite control in citrus groves. Organically, an oil is used to manage them.

California red scale is found statewide, and it is one of the more significant citrus pests in the state. Like spider mites, it's important to monitor populations going into the fall.

California red scale will damage the tree and the fruit. It is a flat-bodied insect that sticks to the fruit surface and will cause it to be downgraded. Scale on the leaves will cause defoliation and branch dieback, resulting in less production the following season.

For conventional groves, several chemical treatments are available. For organic groves, narrow range oil is used to suffocate the insect.

Again, dust will increase scale populations, similar to spider mites. Some groves will have very aggressive populations of scale where annual maintenance may be required, and others may only need to use biological control.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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