Fruit IPM Factsheet

     European Fruit Lecanium

 Scientific Name—Parthenolecanium corni (Bouche)

Reference: Common Tree Fruit Pests, NCR 63,
Angus Howitt, 1993
Michigan State University

Serious outbreaks occurrend in 1894 and 1895 in the plum orchards of New York.  This scale was introduced from Europe.

Life Stages
Egg: A large number—more than 1,000—of white eggs are laid under the bodies of the females during late May or June.  Later, the eggs become pinkish and hatch in late June or July. The egg stage lasts two to four weeks.  After the female oviposits, it dries up into a hard shell on the surface and shrinks away from the eggs that are left inside the shell until they hatch and the young crawl out.   The empties shell eventually becomes loose from weathering and drops the tree.
Crawler: The crawlers are about .5 mm long, flat and yellowish, with legs, eyes and antennae.   After settling and beginning to feed, they secrete a brownish scale cover, becoming spindle-shaped.  The female has three instars and the male has four.  Pupation lasts about one month.  
Adult: The full-grown females are yellowish brown.  They later turn dark brown and are covered with powdery or cotton-like material that looks like the bloom of the plum.  They are oval and elevated in the shape of a spindle.  Full-grown females are 3 to 5 mm long.  The scales of the males are composed of delicate, almost transparent wax, with well marked ridges.

Host Range
Host plants include shade and forest trees. The scale will also attack fruit trees.  The Northern Spy apple has been most frequently attacked.  It has also been found on Wealthy and Transparent; on other fruit trees, including plum, peach, and cherry; and on grapevines.

Injury or Damage
These scales suck the sap from leaves during late July and August and from twigs during May and June of the following year.  The young scales collectively produce a great quantity of the clear, sweet liquid known as honeydew.  This serves as a medium for fungus growth and gives the leaves and fruits a smutty appearance.  They can cause fruit to be undersized and drop prematurely.

Factors Affecting Abundance
Extreme weather conditions—both heat and cold—can cause high mortality. Predators can be a factor in controlling this pest.

Life History
There is one brood per year. Only fertilized females overwinter, as immature small scales on the twigs.  Some of the old, large, dead scales may also be present on the twigs during the winter.  The over wintering young develop in May and June to large brown scales, at which time the females have matured the eggs.  The females’ die, leaving the scales filled with eggs that hatch in July.  The young (crawlers) move to the undersides of the leaves, where they settle and feed along the main veins.  Infested leaves become curled and turn yellow, the tree makes little growth, and the fruits remain undersized or drop prematurely.  The crawlers migrate as far as 1 to 5 feet from the parent female and distribute themselves in a random fashion on the leaves.  After the fist molt, migration back to the twigs usually begins in the late summer and continues until late fall.  Reproduction is almost entirely parthenogenetic.  The distribution of this scale on the twigs is influenced by the age of the wood.  There is fairly uniform distribution on one-, two-, and three- year-old wood, while wood older than three years usually has bark too thick for the stylets to penetrate.

Winged males appear in late August and make with the females, after which the males die.  In the fall, the females crawl back to the undersides of the twigs for the winter.

Monitoring
During the prebloom period, inspect undersides of smaller branches fro brown, spindle-shaped scales.  In mid to late summer, inspect leaves and fruit for black fungus that may develop in honeydew secreted from scales.  To date, there are not pheromones for this pest.

Control
If superior oils are used, they should be applied at the delayed dormant stage, because the European fruit lecanium scale is characterized by rapid growth in the spring that coincides with the development of the host plant.  In the interval from delayed dormant to bloom, the scale grows from the small overwintering form to maturity.  In about 10 days, the weight of the scale may increase tenfold or more. Great changes also occur in metabolic activity as the scale goes from dormancy to active growth.  These metabolic changes affect the respiratory rate, which is directly related to the mode of action of the oil.  Larger animals require greater dosages to produce equal mortality, so the oil becomes les effective as the season advances from delayed dormant to bloom.

*Data from JSU PETE model.

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Created: 10/13/05