Monitoring and management of San Jose scale and other insect pests during the dormant season

This is the time of the year to assess the seasonal activities of certain insect pests in the orchard and make treatment decisions for the delayed-dormant spray. This evaluation provides guidance for planning in-season pest management activities. Insects that can be evaluated using dormant spur sampling includes tiny insects (Scales: San Jose scale, European fruit lecanium; non-webspinning mites: brown mites, European red mites), and overwintered worms (oblique-banded leafroller, oriental fruit moth, peach twig borer). Although dormant spur sampling does not cover navel orangeworm damage evaluation, it is critical to know how much percentage of the mummy nuts are infested with navel orangeworm larvae and follow the proper winter sanitation (see details here).

Scale is a bit different in its lifecycle in comparison to other insects. It is a tiny insect that sucks the plant juices from the plant parts such as spurs, branches, fruits and foliage. SJS females are sac-like, legless insects that are covered by the protective shield, made up of waxy secretion. Since they don’t have legs to move, they are permanently attached to the host plant tissues and feed. Because of the protective cover, often, spray coverage is not sufficient to knock down the population especially in large and dense trees. SJS female and her offspring produce several thousands of progenies in one season. Feeding by a large number of scales can cause significant damage to fruit spurs and scaffolds, leading to reduced tree growth and productivity. In severe cases it can cause death of the new spurs and tree limbs in severe cases. So, knowing the density and/or activities of scales and the natural biocontrol activities on spurs is important for making a treatment decision.

Spur sampling during the dormant season

• Use spur sampling (follow the UC IPM guidelines)
• Take 100 spurs randomly taken from 35-50 trees (inside/outside/high infestation area)
• Out of 100 collected, inspect first 20 spurs first using a hand lens or using a simple dissecting microscope and record the number of spurs with/without mite eggs or live scales. Only do record spurs with or without insect infestation, don’t need to count the numbers of eggs/insects. Parasitized scale has a small hole on top of the scale cap (Picture 1). See pictures of different insect pests need to evaluate from the sample spurs. Treatment threshold: ≥4 spurs with mite eggs or ≥ 4 spurs with live scales. Out of first 20 spurs, if you have <4 spurs infested, continue evaluating next batch of 20 spurs. Further details are available in this sampling form.
• Make treatment decisions based on following guidelines:

Treatment decisions based on the % spur infestation by different insect pests (from UC IPM)

In December 2015, I have collected spur samples from few almond trees that we have in the premise of UCCE-Stanislaus. I have evaluated 20 spurs from each of four varieties using dissecting microscope in the lab. Although infestation varies from orchard to orchard, I have summarized what I have found in the table below.

Dormant oil sprays can be used to control overwintered eggs of European red mites and brown mites, European fruit lecanium, and low to moderate population of San Jose scale. Dormant oil combined with insect growth regulators (Seize or Centaur) spray is effective for medium-to- high population of San Jose scale. PTB overwinter as larvae inside the hibernaculum on tree limbs/crotches. If peach twig borer is only the problem, it is recommended to wait and apply treatment during the spring.

Dormant spray is not effective for: 1) navel orangeworm (larvae overwinter inside the mummy nuts), 2) oriental fruit moth (overwinter in places where sprays are not effective in the dormant season), 3) webspinning spider mites (Pacific-, twospotted-, and strawberry spider mites; they overwinter in soil and/in leaf litters on the ground), 4) plant bugs (overwinter in places such as structures, and other places/alternative hosts outside of the orchard).

Selection of the insecticide to use for the dormant treatment is important. Application of broad-spectrum insecticides (pyrethroids and organophosphates) should be avoided because of the effect of these insecticides to natural enemies, toxicity to bees, and risks of ground water contamination. Moreover, with the recent regulations on dormant season sprays (see link here), choice of suitable insecticide and spray timings in relation to local weather conditions is even more critical.

If high scale populations are the only problem observed in the dormant period, the spray can be moved to the spring. In timing the spring spray, monitor the male scale flight using pheromone traps in the spring. Crawlers (immature, but mobile stage) can be monitored using sticky tapes on tree branches. Apply pyriproxyfen (Seize) and buprofezin (Centaur) at the beginning of crawler emergence, which is 400 DD from the beginning of the male flight. Follow UCIPM guidelines for details about monitoring and suggested products for dormant and spring applications.

Consideration for effective sprays (all season)

• Always follow the label instructions, compatibility while making tank mixes etc.
• Pay attention to weather for effective sprays (avoid rainy, foggy conditions)
• Pay attention to natural enemies, bees etc.
• Calibration of sprayer and equipment, sufficient volume of water
• Minimize spray drifts by shutting the sprayer off while making turns
• Mixing, loading of pesticides in relatively safer places, away from water bodies

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