Scouting for Scale: Seek and Ye Shall Find

SJS white cap stage observed on June 15th, 2016
SJS white cap stage observed on June 15th, 2016

If you are seeing newly developing red spots on apple, they are likely the sign of the first generation San Jose scale (SJS) crawlers, settling down on fruit and beginning to feed. The red dot is a response by the apple to SJS feeding. The white dot center are the 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 13th of June (see this weeks HVRL scouting report). 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 scouting for injury is today. You will need to break open clustered fruit along the orchard edge. This season we’ve found that low numbers of scale are more likely to be found in the tops of trees and within fruiting clusters.

Scouting is essential this week to determine the level of infestation of SJS if control measures up to this point were neglected or ineffective.

The San Jose scale, Quadraspidiotus perniciosus, is a tenacious pest of fruit trees, difficult and expensive to control once it gains a foothold. Female scale 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.

If SJS is showing up in your blocks, 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.

The OP Imidan 70WP and pyrethroids can also be used against the crawlers during emergence in back to back applications at 7-10 days.

Assail (Class 4) is a broad-spectrum neonicotinoid, most effective when directed against crawlers as they emerge.

Centaur 0.7WDG ((buprofezin, IRAC Group 16) acts to inhibit the synthesis of chitin working as an insect growth regulator (IGR). Esteem 35WP (pyriproxifen, IRAC Group 7C), also an IGR, functions as a juvenile hormone mimic, inhibiting metamorphosis from one stage to another. These insecticides are most effective when directed against adults during the pre-bloom early post bloom period. They can be used against crawlers at first appearance yet have no contact toxicity and tend to act slowly. The efficacy of these materials is improved by the addition of oil, however, Esteem 35WP, Centaur 0.7WDG and Assail can be used effectively without the use of oil.

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 to control the nymphs as they feed. An application today 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.

overwintering San Jose Scale with live female (yellow)
overwintering San Jose Scale with live female (yellow)

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

Surround WP Ineffective at Managing SJS.
Surround WP Ineffective at Managing SJS.

About Peter J Jentsch

Peter J. Jentsch serves the mid-Hudson Valley pome fruit, grape and vegetable growers as the Senior Extension Associate in the Department of Entomology for Cornell University’s Hudson Valley Laboratory located in Highland, NY. He provides regional farmers with information on insect related research conducted on the laboratory’s 20-acre research farm for use in commercial and organic fruit and vegetable production. Peter is a graduate of the University of Nebraska with a Masters degree in Entomology. He is presently focusing on invasive insect species, monitoring in the urban environment and commercial agricultural production systems throughout the state
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