WILLOW FLEA WEEVIL AND IMPORTED WILLOW
LEAF BEETLE
Rhynchaenus rufipes (Lec.)
and Plagiodera versicolora (Laich.)
Symptoms and Damage
Willow (and poplar) leaves may be severely browned by these small
insects from mid-summer on. Leaves may retain their normal shape and remain on the trees
but often browned leaves drop abundantly in late August and September. Depending on
severity of attack, the normal green color of leaves attains a bronze or brownish cast
starting in July and becoming increasingly apparent through August.
Willow Flea Weevil
Rhynchaenus rufipes (LeConte)
Description and Life Cycle
Adults are tiny, elliptical, black weevils (0.1 inch long) with orange
legs that eat out tiny circular holes in the foliage, usually from the underside, and
leave only the opposite leaf-surface over the hole. Adults first appear in mid-May as new
leaves are developing. Holes continue to be made into July.
Eggs are laid in leaf punctures by late June. Larvae (grubs) soon hatch
and feed as leaf miners within the leaf tissue, making blotch mines in the upper tissues
of each leaf. Surfaces over the mines become dark brown and blister-like and are very
conspicuous. Mines are completed by mid to late August at which time adults are again
abundant and feeding. With cool weather adults hibernate for the winter in soil, sod, and
under loose bark of trees.
Imported Willow Leaf Beetle
Plagiodera versicolora (Laicharting)
Description and Life Cycle
Adults are oval, stout, metallic, greenish-blue beetles (1/6 inch long)
and make noticeable holes through the leaves (image). They first appear in mid-May and are present
off and on throughout the summer.
Eggs are laid in small masses on the leaves in early June. Larvae
(grubs) soon hatch, feed together in rows, and remove only the leaf surface to leave a
skeleton of leaf veins. Skeletonized leaves become brown. Larvae are jet black; tiny at
first but when full grown are 1/4 inch long. More than one generation occurs. Winter
hibernation is in the same places as for the weevils.
Control*
Bifenthrin, chlorpyrifos or pyrethrin are registered for control of the
willow flea weevil and imported willow leaf beetle. The insecticide should be applied
according to instructions for shade tree pests, during early June (1-11) immediately after
the leaves have flattened out. A second spray application may be required in early July
(1-4) to protect new growth from living adults that have moved in from surrounding
unsprayed trees.
*NOTE: These recommendations are not a substitute for pesticide labeling. Read
the label before applying any pesticide. Pesticide recommendations are contingent on
continued EPA and Maine Board of Pesticides Control registration and are subject to
change.
Caution : For your own protection and that of the
environment, apply the pesticide only in strict accordance with label directions and
precautions.
MAINE DEPARTMENT OF CONSERVATION
Maine Forest Service - Forest Health and
Monitoring Division
April 2000
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