Deadly Biological Parasite of Citrus Pest Can’t Take the Heat of the San Joaquin Valley

Citricola Scale Damage

Citricola Scale Damage

Certain scale insect species feed by sucking juices from citrus trees. Each mature citricola scale produces more than 1000 eggs which hatch into crawlers that settle on the trees. A severe infestation may reduce tree vigor, kill twigs and reduce flowering and fruit set. In southern California, citricola scale is not a problem because they are parasitized by a wasp that lays its eggs in the scale bodies. The wasp eggs hatch and the tiny wasps consume the insides of the scale. However, these deadly parasites are not effective in the San Joaquin Valley where 70% of California’s oranges are grown.

“Citricola scale is a voracious pest that in high numbers can dramatically reduce yield. A typical Valencia orange tree can produce 325 oranges per tree. If there are 10 citricola scale per twig, yields can drop by 70 fruit per tree, a yield loss of more than 20 percent.

The only effective control method in the valley is insecticide treatments. The parasitic wasp that is an effective biological control in Southern California citrus does not control the pest in the valley because of the high populations of scale produced under hotter valley conditions.

Oil will control citricola scale for organic growers, but it may take two applications per season. There is a list of registered foliar and systemic compounds on the UC IPM website.”

Author: Cline, H.
Affiliation: Western Farm Press
Title: Citricola scale valley’s No. 1 citrus pest
Source: Western Farm Press. Friday, 2012-09-28. Available at:

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