Apple-Scale

Includes

Oystershell scale (Lepidosaphes ulmi)

San Jose scale (Quadraspidiotus perniciosus)

Pest description and crop damage San Jose scale was introduced to the U.S. on flowering peach in the 1870s. It is now a pest of all fruit trees and many ornamental and wild trees and shrubs throughout the U.S., particularly in hot, dry climates. Oystershell scale is European in origin and has been in the US since around 1850. 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-shaped. The scale has a tiny white knob in the center with a series of grooves or rings around it. Oystershell scale looks like a miniature oyster. Although oystershell scale is principally a pest of woody parts of the plant (although it occasionally attacks fruit), San Jose scale attacks woody parts and fruit. Scales are closely related to aphids, mealybugs, and whiteflies. Like these insects, they also have piercing-sucking mouthparts. Large populations of scale can devitalize plants and retard growth. Severe infestations by San Jose scale can kill twigs and even the whole tree. Large quantities of honeydew are produced, which makes leaves and fruit shiny and sticky. Sooty mold fungus may colonize the honeydew, giving the plants a dirty, sooty appearance, further restricting photosynthetic activity. Fruit damaged by San Jose scale is characterized by red halos that form around the feeding site.

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 scales, called "crawlers," are very small, flattened, and yellow, and move around on bark and foliage before settling down to feed. Young scales 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 scales do not move. Crawlers are found during June and July and again in August to September, so there are two generations per year. Oystershell scale overwinters as eggs under the female scale. Crawlers emerge in May and June and move to feeding sites on the bark. They secrete a waxy coating and the females remain sedentary. Males emerge from their coating and mate with the females, which lay eggs beneath their bodies, gradually shrinking in size and dying after the last eggs are laid. There is one generation per year.

Scouting and thresholds Inspect twigs during the dormant season for scales. Pay particular attention to weak plants. Observe the young bark for purplish-red halos which indicate infestation. The crawlers are best observed during June to July with a 10X magnifying glass. Crawlers can be monitored by wrapping a piece of double sided tape around an infested branch or by applying a tacky insect glue barrier.

Management-biological control

Larvae of green lacewings and other insects are aggressive predators of scale. However, biological control does not necessarily prevent significant scale infestations.

Management-cultural control

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 scales to catch the crawler stage. As with aphids, avoid excessive nitrogen fertilizer, as this favors increases in scale populations.

Management-chemical control: HOME USE

Stages 0-1: Egg control with dormant & delayed-dormant sprays

Oils are effective against the San Jose scale, but are not very effective against oystershell scale. Apply sprays during dormant or delayed-dormant period (March to April). Do not use after pink appears in buds. Use enough water to cover the tree thoroughly including small limbs and shoots.

  • horticultural mineral oil-Some formulations OMRI-listed for organic use.
  • horticultural mineral oil, plus one of the following: lime-sulfur, lime-sulfur materials such as polysulfide-Some formulations are OMRI-listed for organic use.

Spring and summer

Insecticide applications are aimed at the vulnerable crawlers during mid-summer. Apply insecticides about 10 days after full petal fall (all petals are off) or 17 to 21 days after full bloom. Avoid making applications of insecticides to plants in bloom to avoid bee injury. Follow all label directions.

  • acetamiprid
  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • carbaryl-Highly toxic to bees.
  • gamma-cyhalothrin-Highly toxic to bees.
  • imidacloprid-Soil drenches may have residual activity in woody plants lasting for 12 or more months. If short-term management is the goal, consider other approaches.
  • insecticidal soap-Some formulations OMRI-listed for organic use.
  • lambda-cyhalothrin-Highly toxic to bees.
  • malathion-Highly toxic to bees.
  • permethrin-Highly toxic to bees.
  • plant-derived essential oils-Some have shown efficacy against scale. Some formulations are OMRI-listed for organic use.
  • pyrethrins (often as a mix with other ingredients) -Highly toxic to bees. Some formulations are OMRI-listed for organic use.
  • spinosad-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin-Highly toxic to bees.

Management-chemical control: COMMERCIAL USE

Stages 0-2: Egg control with dormant & delayed-dormant sprays

  • buprofezin (Centaur WDG ) at 34.5 oz/a applied as a ground application using a minimum of 20 gallons of water per acre. Do not make more than one application per growing season. REI 12 hr. [Group 16]
  • chlorpyrifos (Lorsban 4E) at 1.5 to 4 pints/a + horticultural mineral oil at 6 to 8 gal/a in up to 400 gal water. Cold or dry conditions may cause Lorsban 4E oil sprays to infuse into trees, resulting in bud damage or bud drop. Do not apply until winter rains or irrigation has replenished soil moisture such that bark and twigs are not desiccated. . Only one application of chlorpyrifos can be made per year. Do not apply Lorsban 4E after postbloom. REI 4 days. [Group 1B]
  • diazinon (Diazinon 50W) at 4 lb/a + horticultural mineral oil at 6 to 8 gal/a in up to 400 gal water. Do not apply more than one application as a dormant spray per year. REI 4 days. [Group 1B]
  • horticultural mineral oil at 4 to 8 gal/a in up to 400 gal water. REI varies by formulation- See label.
  • lime sulfur (calcium polysulfide)-Formulations vary; see label for rates. May be mixed with horticultural mineral oil at 6 to 8 gal/a in up to 400 gal water. REI 2 days. Some formulations are OMRI-listed for organic use.
  • methidathion (Supracide 2E) at 8 pints/a in up to 400 gal water + horticultural (light) mineral oil at 1.5 gal per 100 gal water. Do not use Supracide beyond the delayed-dormant period. Do not exceed one application per acre per year. REI 3 days. [Group 1B]
  • pyriproxyfen (Esteem 35WP) at 4 to 5 oz/a plus horticultural mineral oil at 4 to 8 gal/a in up to 400 gal water per application. Do not exceed two applications per season. Do not apply earlier than 14 days after last Esteem treatment. REI 12 hr. [Group 7C]

Stages 3-4: Prepink & tight cluster sprays

  • buprofezin (Centuar WDG) at 34.5 oz/a applied as a ground application using a minimum of 20 gallons of water per acre. Do not make more than one application per growing season. REI 12 hr. [Group 16]
  • diazinon (Diazinon 50W) at 4 lb/a in up to 100 gal water per application. Do not apply more than one application as a dormant spray per growing season. REI 4 days. [Group 1B]
  • pyriproxyfen (Esteem 35WP) at 4 to 5 oz of product/a per 100 gal water per application. Do not exceed two applications per season. REI 12 hr. [Group 7C]

Pink & petal fall sprays

  • buprofezin (Centuar WDG) at 34.5 oz/a as a ground application using a minimum of 20 gallons of water per acre. Do not make more than one application per growing season. REI 12 hr. PHI 14 days. [Group 16]
  • pyriproxyfen (Esteem 35WP) at 4 to 5 oz/a in up to 100 gal water per application. Do not exceed two applications or 10 oz/a per growing season. REI 12 hr. PHI 45 days. [Group 7C]

Spring and summer

Long-term control can be achieved only with delayed-dormant sprays; however, fruit infestation can be prevented with summer applications.

  • acetamiprid (Assail 70WP) at 3.4 oz/a in up to 100 gal water per application. Do not make more than 4 applications per year or exceed 13.5 oz/a per growing season. Will provide suppression. REI 12 hr. PHI 7 days. [Group 4A]
  • buprofezin (Centaur WDG) at 34.5 oz/a as a ground application using a minimum of 20 gal water per acre. Do not make more than one application per growing season. REI 12 hr. PHI 14 days. [Group 16]
  • diazinon (Diazinon 50W) at 4 lb of product/a in up to 100 gal water per application. Do not apply more than one application as an in-season spray. REI 4 days. PHI 21 days. [Group 1B]
  • imidacloprid (Provado 1.6F) at 8 fl oz/a in up to 100 gal water per application. Do not use within 10 days prior to bloom or when bees are actively foraging. Do not apply more than 40 fl oz product/a per growing season. REI 12 hr. PHI 7 days. [Group 4A]
  • pyriproxyfen (Esteem 35WP) at 4 to 5 oz/a in up to 100 gal water per application. Do not exceed two applications per growing season. REI 12 hr. PHI 45 days. [Group 7C]
  • spirotetramat (Movento) at 6 to 9 fl oz/a. Do not exceed 25 fl oz /a per growing season. Apply after petal fall. REI 24 hr. PHI 7 days [Group 23].

Related Links