Lecanium scale

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General Description

The European fruit lecanium is the most common species in the Southern Interior.

Hosts

Stone fruits are preferred hosts but it will attack pome fruits and many related ornamental trees and shrubs.

Damage

Russet and sooty mold growth on fruit and limbs caused by the honeydew produced by the nymphs (crawlers). Chronic and/or severe infestations can slow tree growth, reduce fruit size, and eventually kill limbs.

Identification

Egg - Oval, pearly white, laid under the shell of female scales (Fig.1).

Figure 1. Mature eggs exposed under female scale (left). (H. Philip)

 

Nymph (crawler) - Newly hatched crawlers are oval, flat and orange-pink in colour, and the only mobile stage; gradually develop a shell for protection.

Adult - Males are very small delicate winged insects that can walk or fly in search of female scales. Female scales appear as large  (3-5 mm diameter), round raised growths on limbs, and chestnut brown in colour (Fig. 2). They do not move.

Figure 2. European fruit lecanium on water oak (Quercus nigra ) - 1540602 Lacy L. Hyche, Auburn University, Bugwood.org

 

Life History

Nymphs overwinter on host trees, maturing into adult scales in the spring. Male scales emerge from under their scale and seek female scales. Mated females lay their eggs under their scales which hatch into crawlers from late May to mid-June. Crawlers are dispersed among trees by birds, insects, and orchard workers, and also by wind currents. Crawlers move to leaves where they feed until fall when they move back to current year's shoots to settle and develop a protective shell under which to continue development the following spring. There is only one generation per year.

Monitoring

Examine trees in the spring in for the presence of developing scales and continue to observe until eggs are noticed under the scales (use hand lens). To detect the emergence of crawlers to time chemical sprays, wrap double-sided sticky tape around twigs with scales under which eggs were found. Inspect the tape daily using a hand lens until crawlers are found stuck to the tape, indicating crawler emergence and dispersal is in progress. Continue to inspect the tapes until no further activity is noticed. Also inspect trees for presence of honeydew and soorty mold on fruit and leaves. Crawlers are the only stage susceptible to chemical sprays in the summer.

Management

Biological Control

Ladybird beetles, lacewing larvae and predaceous bugs feed on crawlers as they emerge from under their mothers' scales and disperse to leaves to feed. A tiny parasitic wasp also attackes mature scales, which leaves a small round hole in the scale after emeging as an adult wasp. These natural enemies can usually keep lecanium scale below damaging levels if not disrupted by harmful chemicals.

Cultural Control

Prune out infested branches in spring and destroy.

Chemical Control

Chemical sprays to conrol this occasional pest are best directed against the crawler stage. A second spray may be required if egg hatch is prolonged due to cooler spring weather. A delayed dormant spray can aid in control of mature scales. In both cases thorough coverage is essential.