Pest description and crop damage San Jose scale can be differentiated from other scale insects by the scale (shell) that covers the adult females. The scale is hard, gray to black, and cone-shape. The scale has a tiny white knob in the center with a series of grooves or rings around it. Scale insects are closely related to aphid, mealybugs, and whiteflies. Like these insects, they also have piercing-sucking mouthparts. Large populations of scale can devitalize plants and stunt growth. Severe infestations can kill twigs. Scale insects produce large quantities of honeydew, which makes leaves and fruit shiny and sticky. Sooty mold fungus may grow on this, giving the plants a dirty, sooty appearance and reduce quality of the fruit.
Biology and life history San Jose scale overwinters in an immature state and is black in color. In spring, the tiny winged males emerge and mate with wingless females. Females give birth to live young about a month later (no eggs are seen). The young scale insects, called "crawlers," are very small, flattened, and yellow, and move around on bark and foliage before settling down to feed. Young scale also can be dispersed by wind, rain, irrigation, or by the movement of people and machinery. A few days later, they secrete a waxy coating over their body that protects them from pesticides. From this point, female scale insects do not move. Crawlers can be seen during June and July, and again in August and September; there are two generations per year.
Scouting and thresholds Inspect twigs during the dormant season. Pay particular attention to weak plants. Observe the young bark for purplish-red halos, which indicate infestation. The crawlers are best observed during June-July with a 10X magnifying glass. Crawlers can be monitored by wrapping a piece of double-stick tape around an infested branch.
- Larvae of green lacewings are aggressive predators of scale.
Avoid excessive nitrogen fertilizer, as this favors increases in scale populations.
Home gardeners: Scale can be rubbed off plants by hand with a glove or toothbrush. Major infestations can be pruned off. Tanglefoot, "stickem," or a similar adhesive can be applied around infestations of adult scale to catch the crawler stage.
Management-chemical control: HOME USE
- superior-type oil-Some formulations are OMRI-listed for organic use.
- esfenvalerate (for use on gooseberry only)
- kaolin-When applied as a spray to leaves, stems and fruit, it acts as a repellent to some insect pests. Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- azadirachtin (Neemix and other brands)-Consult label for rate. PHI 0 days. Some formulations are OMRI-listed for organic use.
- bifenthrin (Brigade and other brands) at 0.033 to 0.1 lb ai/a. PHI 1 day. Make a cover spray application when crawlers first emerge. Toxic to bees; do not use when bees are foraging. Also toxic to fish and other aquatic invertebrates.
- horticultural oil (several brands)-Consult label for rate. Apply oil while plants are dormant and when temperatures are above freezing. Some formulations are OMRI-listed for organic use.
- insecticidal soap (M-Pede and other brands)-Consult label for rate and use directions. PHI 0 days. Apply when crawlers first emerge. Some formulations are OMRI-listed for organic use.
- malathion (several brands) at 1.25 lb ai/a. PHI 1 day. Apply when crawlers appear, as a spray in 100 gal water/a. After June, use 150 to 200 gal water/a. Toxic to bees; do not use when bees are foraging. Also toxic to fish and other aquatic invertebrates.
- pyriproxyfen (Esteem or Knack) at 0.1 lb ai/a. PHI 7 days. Apply at either dormant, delayed-dormant, or as an in-season cover spray targeted at the crawlers. For dormant or delayed-dormant applications, use with a horticultural oil.
- spirotetramat (Movento) at 0.13 to 0.16 lb ai/a. PHI 7 days. Movento is known to suppress lecanium scale and may be helpful with suppression of San Jose scale.