Application
Timing Decisions to Maintain Biocontrol
of Cottony Cushion Scale
David Haviland, UCCE Entomology Advisor-Kern Co. and
Beth Grafton-Cardwell, UC Entomology Extension Specialist- Kearney Ag. Center
Prior to the introduction of vedalia beetle into California in 1888, cottony cushion scale was a devastating pest of citrus. Now, serious problems with cottony cushion scale generally occur only when new broad spectrum insecticides, such as pyrethroids, insect growth regulators and neonicotinoids are used for one or more citrus pests, disrupting the highly effective vedalia beetle. The severity of the disruption depends on application timing, the rate and application method, and the number of applications per season.
Laboratory and field studies have shown that neonicotinoid insecticides, including Admire, Assail, and Provado, are toxic to vedalia beetles. Mortality occurs when foliar applications come in contact with the beetle, or when larvae or adults feed on cottony cushion scale that have ingested one of these insecticides from a systemically or foliarly treated tree. Since cottony cushion scale is not susceptible (and the vedalia beetle is), growers should properly time these insecticides when they have a cottony cushion scale population.
Admire treatments for glassy-winged sharpshooter are generally applied just prior to bloom (late March), or just after petal fall (late April, early May). In areas where cottony cushion scale is a concern, Admire applications should be postponed until after petal fall. This application timing (late April or early May application plus 4-6 weeks for uptake) will allow time for vedalia beetle to grow and develop during the March to May period when it naturally cleans up scale. Mortality to vedalia after this period is less of a concern as their populations naturally disperse or decline in the summer heat.
Monitoring for cottony cushion scale in the spring is recommended prior to setting an application date for Admire. To monitor, check 20 trees per every 10 acres for the presence or absence of live cottony cushion scale. If more than 5% of the trees have live scale, delay Admire applications until after petal fall.
Admire is the preferred
treatment of glassy-winged sharpshooter in citrus because it is long lasting
(5-6 months) and selective, allowing most natural enemies to survive with the
exception of vedalia beetle. An
added benefit of Admire is that it can provide suppression of red scale and
citricola scale.
Assail and Provado are two other
options for control of glassy-winged sharpshooter.
Assail (acetamiprid), is shorter lived than Admire (2 months), and may be
more disruptive of natural enemies because it is applied to the foliage.
When live cottony cushion scale is present on 5% of the trees, Assail
should not be used until vedalia has finished its job around early June.
Provado (foliar imidacloprid) is effective against citricola scale and
glassy-winged sharpshooter, but because it has been shown to cause flare-ups of
red scale, it is not recommended for use in citrus.
By following these recommendations, growers can successfully integrate Admire and Assail applications into their integrated pest management programs without severely disrupting the benefits of their biological control organisms.