How Does the San Jose Scale Spread? A Full Analysis of Control Measures

I. Distribution and Damage

The San Jose scale (Quadraspidiotus perniciosus) in the Korla region mainly damages pear, apple, apricot, peach, hawthorn, grape, and white poplar, among other fruit trees and forest trees. The insects cluster densely on the branches and trunk in the upper canopy and inner part of the crown, with more on smooth-barked areas and the sunny side. Population density is highest on 2- to 5-year-old branch sections, and on 1-year-old branches they mainly gather around the bud bases.

The San Jose scale sucks the sap of branches, leaves, and fruit as female adults and nymphs. Young branches and leaves dry up and fall off after being damaged; damaged fruit develops purplish-red sunken spots, forming misshapen fruit; after branches and the trunk are damaged, the cortex becomes corky, and the phloem and vessel tissues die, weakening the tree's vigor in mild cases and causing branches and the trunk to die in severe cases.

II. Life History and Habits

The San Jose scale has 3 generations per year in the Korla region, overwintering as 1st- to 2nd-instar nymphs on branches and the trunk. When sap begins to flow in spring, the overwintering-generation nymphs begin to feed; male adults appear in mid-May, and after mating the males die; fertilized female adults begin ovoviviparous reproduction of the 1st-generation nymphs in late May to early June, with the peak in early to mid-June and the end in mid-July, and the birthing period lasts more than 1 month. The 1st-generation female adults begin giving birth in late July, enter the peak in early August, and a small number of nymphs are still active in early September; the 2nd-generation female adults give birth from mid-September to mid-October.

III. Transmission Routes

1. Wind transmission

Because the San Jose scale is small, when it encounters wind during the peak reproductive period, it spreads to pear orchards through the wind and causes damage.

2. Transmission by branches, leaves, and fruit

It spreads from insect-infested branches, leaves, and fallen fruit carried by the tree to areas where it has not yet occurred and causes damage.

3. Migration flight transmission

The male San Jose scale spreads and causes damage through short-distance migration flight.

4. Transmission by uncomposted organic fertilizer

Fruit growers fertilize pear trees with weeds from pear orchards and feed livestock with uncomposted insect-infested branches and leaves, thereby spreading the pest and causing damage.

5. Transmission by pruning tools

It can be spread and cause damage through pruning saws and grafting knives.

IV. Control Methods

For trees with insects on only 1 to 2 branches, manual brushing and wiping of the overwintering nymphs can be used, or the insect-infested branches can be cut off during winter pruning and transported out of the orchard to be burned. For individual taller trees, during the sap-flow period, rotten cotton wadding soaked in a 30- to 50-fold dilution of Supesha pesticide solution can be tied around the trunk with the loose bark scraped clean, with a width of 20 to 30 cm, covered on the outside with plastic film, and the top and bottom openings tied tightly to prevent the pesticide solution from evaporating quickly. Repeating this 2 to 3 times before the end of April can effectively control the damage of the San Jose scale.

For pear orchards with a relatively large affected area and severe damage, spray 5 degrees Be lime sulfur mixture or a 100-fold dilution of Rongsha Jieman in late March. In early May, before the overwintering-generation nymphs form a waxy shell, and from early June to mid-July, during the emergence period of the overwintering-generation nymphs and the birthing period of the females, are favorable times for control. Spraying 40% Supesha 1000-fold solution, 25% Aikashi 1500-fold solution, or 40% Jiefenke 800- to 1000-fold solution gives good control efficacy.

During the growing season, try to avoid using broad-spectrum insecticides with long residual activity, so as to help protect natural enemies.