How to Manage Pests
UC Pest Management Guidelines
Black scale is the most common soft scale (family Coccidae) in California avocado. Other species occasionally present include brown soft scale, European fruit lecanium, and hemispherical scale. Pyriform scale occurs on avocado in landscapes, but is absent or rare in commercial groves.
Soft scales at maturity are 0.08 to 0.2 inch (2–5 mm) in diameter. The soft scale's surface is the actual body wall of the insect and, unlike armored scales, cannot be removed. Adults are black, brown, or orangish with a hemispherical, humped, or roundshape. The exception is pyriform scale, which is flattened and somewhat deltoid (pointed at one end and rounded at the other). White wax projects from beneath the margin of female pyriform scales.
Mobile first instars (crawlers) emerge from eggs laid under the female's body. First instars settle to feed within a day or two of emergence. These nymphs are oval and yellow, pale orange, or reddish. Soft scales retain barely visible legs and are able to move slowly, as they molt through three instars. On evergreen hosts such as avocado, after the crawler stage scales usually spend the rest of their life in one spot.
Soft scales rarely are pests in avocado. They suck phloem sap from foliage and twigs. Rarely do they feed on fruit. Where soft scales are common, the large quantities of sticky honeydew they excrete promotes growth of blackish sooty mold, which can foul fruit.
Treating scales is rarely warranted. Soft scales usually are controlled by predators and parasites. Conserve natural enemies by reducing dust and selectively controlling sugar-feeding ants. Whenever possible, apply only selective or short-residual pesticides to control other pests.
Parasitic wasps are especially important in controlling scales. Parasites include Coccophagus spp. (family Aphelinidae) and Metaphycus and Microterys spp. (Encyrtidae). Scale-feeding lady beetles include Chilocorus, Hyperaspis, and Rhyzobius species and along the south coast, the steelblue lady beetle (Halmus chalybeus). Lady beetles can easily be overlooked because many are tiny, colored and shaped like scales, or (as small larvae) feed hidden beneath scales' bodies. Lacewings, predaceous bugs, and predatory mites are among the other invertebrates that at least occasionally feed on scales.
UC IPM Pest Management Guidelines:
UC ANR Publication 3436
J. G. Morse, Entomology, UC Riverside
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
M. S. Hoddle, Entomology, UC Riverside