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Ask Your PCA: Which summertime pests threaten citrus?

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Issue Date: July 14, 2021
Chris Boisseranc, PCA, Southwest Ag Consulting Inc., Redlands
Chris Boisseranc, PCA, Southwest Ag Consulting Inc., Redlands

During the warm season, there are several pests that are damaging to citrus. They will become more active, and their populations can explode very quickly as temperatures rise.

California red scale, or CRS, is one of the more economically damaging pests, and it's widely distributed throughout the state. It has a biocontrol agent: Aphytis melinus, a parasitic wasp.

Beneficials are released early in the season to reduce the pest population, but in some warmer regions, biocontrol alone won't control the pest. If the pest levels remain too high, then a chemical treatment is applied.

There are several organic and conventional chemicals available for CRS. Typically, CRS is treated with an insecticide and often it is mixed with a narrow-range oil. The oil has a suffocating action that kills the eggs, adults and even the crawlers.

The mealybug is similar to CRS, in that it's a soft-bodied insect. The mealybug's most destructive aspect is that it produces a honeydew excrement, a sugary substance that attracts ants into the canopy. Black and Citricola scale also produce honeydew. The ants will protect the insects producing the honeydew, resulting in heavier populations of the pests.

Mealybugs gather at the top of the fruit and drip the honeydew down the fruit. A fungus called sooty mold will grow on the honeydew and cause blackening of the fruit and canopy. The mold can cause defoliation and reduction both of fruit quality and of future productivity of the trees.

When making applications for scale and mealybugs, it's advised to use materials that are appropriate for controlling Asian citrus psyllid. The psyllids also produce honeydew, and they are promoted and protected by ants, too.

The goal should be to stay ahead of the honeydew-creating pests, which will keep ant numbers low and create an environment that isn't as accessible to ACP.

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

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