Fruit IPM Factsheet

San Jose Scale

Scientific Name Quadraspidiotus periciosus (Comstock)

Reference: Angus Howitt, 1993. Common Tree Fruit Pests, NCR 63, Michigan State University

San Jose Scale was brought into California about 1870. By 1873, it had become a serious pest in the San Jose Valley; hence, the name. Marlett went to the Orient in 1901 to find the native home of the scale and found that it originated northwest of Beijing on Chinese peach. In 1886, it was brought into New Jersey on plums. The two nurseries receiving this material shipped nursery stock to all parts of the country. By 1895, it had reached all parts of the United States.

The first insect resistance to pesticides—San Jose scale’s resistance to lime sulfur—was reported in the United States by Melander in Washington in 1908. Tremendous damage was done by this pest before controls were perfected. In 1922, 1,000 acres of mature apple trees were killed in southern Illinois.

Life Stages
Egg: The female scale does not lay eggs but gives birth to living young.
Crawler: Crawlers are minute, orange-yellow and oval, with six legs and one pair of antennae.
Adult: The females are nearly round and about 1.6 mm across with raised nipple in the center, and they remain under their scale coverings their entire lives. The males are oval, about 1 mm long and half as broad, with a raised dot near the larger end of the scale. This waxy covering protects the male. It emerges from the scale as a small, yellow two-winged insect.

Host Range
Host plants include apple, pear, quince, plum, apricot, sweet cherries, currants, gooseberries and other woody ornamentals.

Injury or Damage
San Jose scale feeds on the sap of the host plant. The amount of sap that a single individual, or even several hundred individuals, could extract could not injure a healthy tree or shrub. But the species multiplies so rapidly that millions of progeny may be produced from a few scattered parents in a season or two—enough to completely cover the bark of parts or even all of the trees.

Most of our insect pests have natural enemies that restrain their multiplication so that they become destructively abundant only now and then, but the enemies of the San Jose scale are inadequate to control it. The scale may kill a young tree or shrub in two or three years; older trees withstand the attack longer, but sooner or later they are like-wise destroyed. Young orchards are killed out more quickly than old ones; and where young trees are set in old infested orchards, they also become infested and die before they are old enough to fruit.

The scale does not confine its attack to the bark of the tree but infests the leaves and fruit also. The fruits of apple, peach and pear trees frequently become as badly infested as the bark. On fruit and on young bark, the scale produces a conspicuous red spot. It is comparatively easy to prevent serious injury to the tree by using proper control measures, but it is very difficult to prevent some spotting of the fruit. Scaly fruit is unsightly and not marketable.

Factors Affecting Abundance
Adverse weather conditions, including winds, rains and extreme heat and cold, can cause heavy mortality. Predaceous and parasitic insects check the multiplication of this pest t a certain degree. Very low winter temperatures can cause high mortality of the early instar nymphs.

Life History
This insect passes the winter a partly grown scales on the tree. Up to 80 percent of the winter forms may be first-nymphal instats. The insects remain dormant, tightly fastened to the bark, until the sap starts flowing in the spring. They then begin to grow, usually becoming full grown in late May. At this time, the active males which are tiny, two-winged insects, come out from their scales to mate with the females. (The females remain under scales throughout their lives.) The females continue to grow for a month.

After mating, the females begin to produce living young, usually at the rate of nine or 10 per day. They reproduce for about six weeks, each female bearing from 150 to 500 crawlers. Crawlers have six well developed legs and two antennae and can crawl considerable distances during their first few hours of life. They will crawl about for a few hours until they find a place attractive to them. Then they will insert their slender, threadlike mouthparts through the bark and begin sucking sap. About three weeks later, they molt and shed their skin. The scales then become mere flattened, yellow sacs with waxy caps. They are attached to the bark by their sucking mouthparts.

As the insect grows, woolly secretions given off form the body are mixed with a waxy material to continue the formation of the shell. Portions of the shed skins are also incorporated into the scales after molting. The females develop through two nymphal instars to the adult. The males develop through four instars. The last two are called prepupa when the legs are short and thick.

This insect increases most rapidly in hot, dry weather. The descendants of a single female could number more than 300 million a year. Crawlers are spread by wind, on birds’ feet, on workers’ clothing and on farm implements.

There are two generations per year. Because the females bear living young over so long a period, the broods overlap and all stages may be present on the trees through-out the growing season. In the summer, each generation is completed in five to seven weeks, depending on the weather. Natural enemies include parasitic wasps and lady bird beetles.

Monitoring
Because of their small size, San Jose scales may go undetected until they appear on the fruit. Scales on the fruit indicate a need for control measures the following year. Place pheromone traps in the tree at the pre-pink stage to trap the tiny, yellowish winged males that emerge during the bloom and petal-fall periods. The renew the cap and trap for summer generation. In addition to monitoring male trap catch, monitor crawler populations by placing black, sticky tape around scale-infested scaffold branches about seven to ten days after petal fall. Crawlers will become trapped on the tape when they emerge. Check the tape often for trapped crawlers. Apply an effective pesticide for scales after you see the first crawler.

Using 51 degrees F as a base, degree-days (DD) fro San Jose scale activity* are:

Control
Superior oil applied in the prebloom stage is effective. If high populations are present, an effective insecticide applied at early petal fall will control the males before they mate with the females. First-generation crawlers, which usually begin to emerge four to six weeks after adult male flight, can be controlled with thorough coverage by an effective pesticide applied immediately after capture of the first crawlers on the sticky, black tape. Check the tape often for the presence of crawlers. If it is necessary to control the second-generation of scale, use pheromones to trap the second-generation males and sticky tape to trap the crawlers, and time the sprays accordingly. Degree-days listed for San Jose scale will be useful in determining the seasonal activities of this pest.

*Data from JSU PETE model.

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Created: 9/28/05