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Entomology HomeA free brochure with color photographs published by
the University of California Ag and Natural Resources:
Stages of the
Cottony Cushion Scale (Icerya purchasi) and its Natural Enemy,
the Vedalia Beetle (Rodolia cardinalis)
E. E. Grafton-Cardwell
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CCS/vedalia brochure here
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The cottony cushion scale situation 1998-2005
Cottony cushion scale became a serious problem in many citrus orchards in the San Joaquin Valley during 1998-99 after after major acreage was treated with the insect growth regulators (IGRs), Esteem (=Knack, pyriproxyfen) and Applaud (buprofezin), for California red scale. Vedalia beetle had not experienced these insecticides before and was quite sensitive to them. These insecticides prevent vedalia from completing pupation and emerging as adults and, when Esteem is applied, the beetle eggs do not hatch. The Applaud residues seem to last 2-3 months, while the Esteem residues last > 5 months. A sign that the IGRs are killing vedalia is the presence of dead vedalia pupae on the outside leaves of trees.
Esteem and Applaud will also kill the cottony cushion scale pest, but they kill it very slowly. The orchards that experienced the worst cottony cushion problems in 1999 were not the orchards that were sprayed with IGRs, because the IGRs killed the cottony cushion scale as well as the California red scale. The worst cottony cushion scale outbreaks were in the untreated orchards. The spray drift of Esteem and Applaud applied in June and July in 1998 eliminated vedalia beetles from citrus throughout the San Joaquin Valley for 9 months, not returning until March-May of 1999. During 1998, 50,000 acres of citrus were sprayed with IGRs and the majority of those treatments were Esteem. If vedalia returned in March or April of 1999, they did a great job of cleaning up the cottony cushion scale problem. In some of the orchards, however, vedalia did not return until May which did not give it enough time to clean up the cottony cushion scale infestation before the IGR sprays began again (June 1999). These orchards suffered from very high densities of cottony cushion scale and many had to be treated with Malathion or Supracide. The good news is that vedalia returned to citrus much more quickly in 1999-2001 (by September or October in most orchards) perhaps because 50% fewer acres were treated with IGRs during those years. Currently, fewer orchards have cottony cushion scale problems and most have vedalia beetle adults and/or immatures feeding on the cottony cushion scale. When the weather warms, the vedalia should develop quickly and rapidly overcome the cottony cushion scale.
There are other factors that have exacerbated the cottony
cushion scale problem. The extra spring moisture in 1998 and 1999 and the mild
weather during the summer of 1999 were perfect conditions for soft scale growth
and development. Another problem has been the use of the pyrethroids Baythroid
(cyfluthrin) and Danitol (fenpropathrin) for citrus thrips
control. The pyrethroids are very toxic to vedalia beetles and they are applied during the
time period (April/May) when vedalia beetles may be working to control cottony
cushion scale. Baythroid kills the beetles and prevents them from laying eggs
for a period of several months after treatment if the beetles contact the
residues. The effects of pyrethroids on vedalia are less severe than the
IGRs because the pyrethroids are applied using a lower water volume and sprayed
on the outside of the tree. Other citrus thrips insecticides such as Veratran, Agri-Mek, and
Success do not seem to have any noticeable effect on vedalia beetles. Use of
Baythroid or Danitol sometimes allows cottony cushion scale to get a foothold
and then when the vedalia is eliminated by IGRs, the cottony cushion scale
population explodes. Finally, the systemic application of Admire (imidacloprid)
and the foliar applications of Provado (imidacloprid) or Assail (acetamiprid) that
are used for glassy-winged sharpshooter control are also toxic to vedalia
beetles. Both the beetle and larval stages that feed on cottony cushion
scale that has ingested Admire are killed and the effect lasts for 4-5
months. The effects of the foliar applications are much shorter (1-2
months).
Application
Timing Decisions to Maintain Biocontrol
of Cottony Cushion Scale
The vedalia beetle is the best method of controlling cottony cushion scale. Vedalia are very fast growing, they can complete 4 generations in the time it takes cottony cushion scale to complete one generation. They consume large numbers of cottony cushion scale eggs and nymphs in a very short amount of time. When vedalia beetles arrive in an orchard they can clean up a nasty problem in 4-6 weeks. Insecticides such as Malathion and Supracide are often not as effective as vedalia beetle and are disruptive to the natural enemies need for California red scale control. Esteem or Applaud treatments will kill cottony cushion scale, but they work very slowly (1-2 months for cottony cushion scale to slowly die). If insecticides are needed, it is best to wait until the cottony cushion scale are primarily in the 1st instar stage (June-July) when they are easier to kill.
No commercial insectaries are currently rearing vedalia beetles and so finding them in one orchard and moving them to the next is the best method of establishing vedalia in an orchard. During February-April, simply collect vedalia adults, pupae, or any stages that you can find, and move them into the problem orchard. Place the vedalia in the branches of a tree on top of a cottony cushion scale infestation in several trees in the orchard and they should spread on their own from there. If the conditions are right, one early release of 25-100 vedalia individuals per 10 acre block should be sufficient, but more is always better. They can be moved into a cottony cushion-infested orchard any time of the year, but they seem to do their best in the early spring, especially when the population of cottony cushion scale consists mostly of very large female scale. The vedalia likes to eat and lay it’s eggs on this stage of cottony cushion scale. When the vedalia eat all of the cottony cushions scale, the vedalia will fly away in search of more food.