Armored scale is easy to miss, but infestations can suck the life out of mature trees and shrubs and destroy fruit crops
Description of armored scale
Imagine a tiny, 1/8” dark brown bowl, turned upside down. Underneath this protective cover is a round, squishy insect, with no head or legs visible to the naked eye. Scale insects have a straw like mouthpart that is inserted into bark, fruit, or leaves of citrus and other fruit trees, nut trees, and ornamental trees and shrubs.
Armored scale varieties
Unlike soft scales, armored scales do not produce honeydew. In San Jose, California, we have four varieties of armored scale: oystershell, San Jose, Asian cycad, and euonymus.
Oystershell Scale (Lepidosaphes ulmi)
Oystershell scale has a distinctly elongated shape, unlike the circular shell of most scale insects. Mature specimens can be as large as 2.5 mm long. It favors deciduous trees, such as maple, poplar, dogwood, ash, and willow. This variety lays 20-100 tiny white eggs that can be found under the protective scale shell.
San Jose Scale (Quadraspidiotus perniciosus)
Accidentally imported from Asia in the 1870, San Jose scale attacks apples, pears, and peaches. It is now found throughout North America. This species produce live young, called crawlers. A fertilized female can produce as many as 10 crawlers a day for 6-8 weeks - that’s over 500 offspring per scale!
Asian Cycad Scale (Aulacaspis yasumatsui)
Asian cycad scale was brought to the States from Thailand and China on nursery stock. This pest has a 100% mortality rate for any cycad plant species that it infests. Spray insecticides have not been effective. Cycads are often called “living fossils” because they have been around since before the dinosaurs! While they look similar to palm trees, they are more closely related to pines. The most common cycad species is the Sago Palm.
Euonymus Scale (Unaspis euonymi)
Another Asian import, eponymous scale attacks spindle trees, wintercreeper, Western burning bush, and strawberry-bush across the U.S. They attach themselves to the underside of leaves, causing stippling and chlorosis. Males and females can girdle twigs and branches, causing die-off. Males look like white exclamation marks and females are mottled brown.
Armored scale lifecycle
Scale insects can have up to three generations each year. Male scales are tiny golden winged insects that normally emerge to coincide with apple blossoms. The females emit pheromones that attract the males. Crawlers (nymphs) are bright yellow and they resemble spider mites. They either walk or are blown to a new location where they undergo distinct changes. The first stage (instar) occurs when the nymph secretes a white, waxy covering, known as the white-cap stage. The second instar is called the black-cap stage because a darker scale covering is secreted. If the nymph is male, it will go through two more non-feeding instars before taking flight.
How to control armored scale
San Jose scale is often controlled naturally by several varieties of chalcid wasps and lady beetles. Insecticidal sprays and horticultural oils can be used to reduce infestations. Severely affected limbs should be removed and destroyed. Pesticides can be used effectively, but remember that you are putting poison in your yard.
The best control methods are regular inspections and pruning that improves overall plant health and air flow.
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