Gardening for You: Pesky plum pest
Getting back into the garden, checking out plants just waking up, inspecting branches then finding shiny little globs on a twig. Scale insects are a sneaky, little-detected, piercing, sucking pest that can wreck havoc on a tree.
Scales are unlike many other insects. Females are the iconic scale image – look like legless turtles, are round, waxy, sessile, small, and often brown with smooth, domed bodies. When alive, bodies of females are soft and pliable, but as they die, shells harden and attach loosely to bark. Unless there is a huge infestation, scales can be easily missed since they look like just another bump on a branch.
Adult male scales are entirely different in appearance: they are winged, tiny, about 1 mm in length, and look like gnats.
The scale in the accompanying photograph is likely Lecanium parthenolecanium corni, the European fruit scale, a type of soft scale that is a common pest of more than 50 woody trees and shrubs. Its preferred hosts are Prunus and Malus fruit trees; Prunus, peach and plum; and Malus, apple, pear, and quince.
The female lives under a waxy, domed shell and under her body are several hundred white, creamy, or yellow eggs. Eggs hatch in late April and early May and crawlers, tiny nymphs that look like lice, come out from beneath the mother’s protective scale covering. Crawlers migrate to young leaves, congregating in the veinal areas of leaves as they feed on the leaves’ sugary phloem sap.
As crawlers mature their bodies go through several instars, changing in shape. They continue to mature, overwinter on the bark of small branches, and begin feeding in the spring. Adult males emerge in the spring but it is the female that feeds and damages tissue.
Serious infestations cause leaves to yellow and drop, twigs to die back, stunting growth. Weakened trees become susceptible to infestations of borers and pathogens.
Scale insects are difficult to control because of the waxy body covering. The shell is a natural form of protection from predators, also shielding them from insecticides.
Because of the waxy shell late April and May is the narrow window to control this pest. Spring is when the unprotected crawlers emerge from under the female and are most vulnerable. To confirm infestation, hold a sheet of white paper under the suspect branch; tap the branch and observe what drops onto the paper. If tiny objects move about, these are likely crawlers. Treatment at this stage disrupts its life cycle and interrupts production of subsequent generations.
Control measures include dormant oil application before leaf break as a preventative treatment; locating and removing adult females as a mechanical means; systemic insecticides and contact insecticidal applications in early spring when crawlers are active. Left untreated, populations can explode and become a significant problem.
Note: Some information from extension.umd.edu
Ellen Peffley taught horticulture at the college level for 28 years, 25 of those at Texas Tech, during which time she developed two onion varieties. She is now the sole proprietor of From the Garden, a market garden farmette. You can email her at gardens@suddenlink.net
This article originally appeared on Lubbock Avalanche-Journal: Gardening for You: Pesky plum pest
