San Jose Scale

San Jose Scale is one of the most destructive pests of stone fruits in the United States. Damaging infestations develop before growers are aware of the insect's presence, because of the small size and obscure coloration of the scales. The reproductive rate of this insect is exceedingly high and injurious infestations frequently develop in the few months between harvest and the advent of winter. Dry summers usually check the rapid development of this pest.

An initial symptom of scale infestations is a decline in the trees' vigor, characterized by sparse, yellow foliage. Reddish spots may be found on the underside of infested bark around the areas where the insects have inserted their mouthparts. If control measures are not used, reddish spots caused by the feeding of immature scale insects appear on the leaves and fruit. The leaves fall from the terminals and limbs, cracking and bleeding of the limbs occur and the trees die.

Scales are tiny, orange, sac-like insects beneath light gray, waxy coverings. The round coverings of the full-growth females measure 1/16 inch in diameter. Each scale covering is made up of a series of concentric rings, surrounding a raised nipple near the center. The males have smaller, elongate-oval coverings about 1/25 of an inch in length with the circular. raised dot located near one end rather than near the center.

The females lay eggs which hatch into crawlers. These tiny, yellow insects crawl from beneath the parent scale, find suitable places on the bark, leaves or fruit and insert their threadlike sucking mouthparts. The females never move from the spot selected at this time. After feeding on the sap for 2 or 3 days, the young, or nymphs, secrete their initial scale coverings which are later enlarged. In 2 or 3 weeks the males develop into delicate two- winged insects which emerge from their scales and die soon after mating with the sac-like stationary females.

Scale insects in all stages of development exist throughout the year, except during periods of extremely cold weather. Mature females and nymphs survive the few days of Texas' cold weather which normally occur in December and January. During these periods, embryonic development within the females apparently ceases and adult males and crawlers do not appear.

WHITE PEACH SCALE

White peach scale is a pest of many trees and shrubs. The damage resulting from the feeding activities of this species is similar to that caused by San Jose Scale.

Female scales are circular and grayish with a yellow-to-orange raised center. The male scales are small and more elongated than the females'. In cases of severe infestations, they appear as white, cottony masses encrusting the bark of the tree.

Soft Scale

Several species of soft scales attack plums and peaches in Texas. Attacks by these insects are infrequent and usually infestations are not severe enough to require control measures.

These pests are brown, soft-bodied scale insects with coverings larger and more convex than those of San Jose scale. Usually, the soft scales are located on the underside of twigs. Young individuals, which may be motionless on the leaves in the summer, migrate to the twigs in the fall. During summer feedings, the young scales secrete a clear, sticky liquid called honeydew which drops on the leaves and fruit. Dark, sooty masses of fungus grow on the honeydew and discolor the foliage and fruit.

Suggested Control of Scale Insects on Peaches and Plums

Treat trees in late dormant season, but before pink bud. Thorough coverage of the tree is essential. If spraying with an airblast machine, make application to both sides of the tree.

Insecticide and Rate

Petroleum oil: Use 1.5 to 2 gal. Per 100 gal.

To enhance control with oils, tank mix one of the following insecticides with the oil. Refer to the product label for rates:

Chlorpyrifos (Lorsban 4E)
or
Diazinon (Diazinon 50WP)
or
Methidathion (Supracide 2E or 25 WP)
or
Phosmet (Imidan 70 WSB)

Remarks

Adding insecticides to oils improves control.

Do not use oils when the temperature is below 32 degrees F. or above 90 degrees F.

Do not combine sulphur sprays with oils on foliage and do not follow a previous application of sulphur or apply sulphur following an oil spray for at least 30 days.

Note: In years of abundant summer rainfall, scale populations frequently increase following the harvest of fruit. The growth of heavy foliage and succulent twigs provides ideal conditions for scale development. During these periods, growers should make inspections to determine the need for additional sprays. Also, scale insects can rapidly reproduce on trees in years when there is a crop failure due to weather conditions because producers do not normally carry out a spray program when this happens. It is strongly advised that producers inspect trees in years of crop failure for scale insects. Studies indicate that scale crawlers develop from eggs in early April. Upon finding scale crawlers during this time, a single application of an insecticide to the trees is advised.

JVR 97

References to commercial products or trade names are made with the understanding that no endorsement is implied and no discrimination is intended by the Texas Agricultural Extension Service. Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socio-economic level, race, color, sex, religion or natural origin.

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Last modified: June 23, 1998 by Andrew Perrone