San Jose Scale Damage Increasing on Hudson Valley Apple

The San Jose scale, Quadraspidiotus perniciosus, is a tenacious pest of fruit trees, difficult and expensive to control once it becomes established. Female scales produce approximately 400 young “crawlers” over a 6-week period requiring insecticide residue over two applications to manage the crawler population during this extended period of emergence. Scouting is essential this week to determine the level of infestation of SJS if control measures up to this point were neglected or thought to be ineffective.

If you are seeing newly developing red spots on apple, they are likely the sign of San Jose scale (SJS) crawlers during the emergence period, settling down on fruit and beginning to feed. The red dot, a response by the apple to SJS feeding, will have a white dot center (SJS nymph in the white cap phase), turning black as nymphs mature. As they mature they become more difficult to control.

Emergence was predicted to begin on or after the 16th of June and given the number of scale showing up on fruit of infested trees it appears the prediction was quite close to this date. If you had SJS on your fruit last season AND did not make applications against this insect during the pre-bloom or early post-bloom period, the window for applying an effective insecticide beginning last week will continue for about 5-6 weeks. If SJS is now showing up, applications of effective insecticides should be made at the earliest application window. Choices available for SJS management include Admire Pro 4.6SC at (2.8 fl.oz./A) a feeding toxicant, Assail 30SG (8.0 oz./A) a translaminar feeding and contact insecticide, Centaur 0.7WDG (34.5 oz./A) and Esteem 35WP (4-5 oz./A) insect growth regulators; Imidan 70WP 70WS (2.13-5.75 lb./A), contact insecticide; the pre-mix insecticides Endigo ZC (5-6 fl.oz./A), Leverage 360 (2.4-2.8 fl.oz./A) and Voliam Xpress EC (6-12 fl.oz./A) include contact and feeding activity.

A number of choices are available for SJS management. Centaur 0.7WDG acts to inhibit the synthesis of chitin (Class 16) working as an insect growth regulator (IGR). Esteem 35WP, also an IGR, functions as a juvenile hormone mimic, inhibiting metamorphosis from one stage to another (Class 7). These insecticides are most effective when directed against crawlers at first appearance yet have no contact toxicity and tend to act very slowly.

Assail (Class 4) is a broad-spectrum neonicotinoid that also is most effective when directed against crawlers as they emerge. The efficacy of these materials is improved by the addition of oil, however, Esteem 35WP and Assail can be used effectively without the use of oil. The OP Imidan 70WP and pyrethroids can also be used against the crawlers during emergence in back to back applications at 7-10 days.

Remember, rotating classes of insecticides for each generation will delay the onset of resistance. Making multiple applications of the same class or same insecticide at a 7-10-day interval for the same generation is recommended.

Movento requires a two week window and will be ineffective for this early stage of emergence. However, If you’re trying to clean up a robust population, Movento PLUS OIL or a penetrant such as LI700 at a penetrating rate should be applied along with a contact insecticide to manage this early stage of emergence. Our research suggests that the use of a single application of Movento + penetrant using the high labeled rate of 9 fl.oz./A provided very good commercial control of the pest.

For organic tree fruit growers, oil is the best cure for SJS. Kaolin Clay, the active ingredient of Surround WP, has no efficacy against the emerging crawlers. Keep oil away from applications of sulfur used for disease management to avoid phytotoxicity to fruit and foliage.

The Cornell fact sheet describes in depth San Jose Scale life cycle and biology.