HEMLOCK RUST MITE
DESCRIPTION
The Hemlock Rust Mite, as this p
est is sometimes called, belongs to
a group of microscopic mites referred to as eriophyids.
The adult Hemlock Rust Mite is not visible to the naked
eye. A 10-20X hand lens is needed to glimpse the mite,
and much higher magnification is required to identify it
to species. The orange to pink adult is about 0.25 mm
long, wedgelike, and has a pair of long, anteriorly
pointing setae located dorsally behind the second pair of
legs.
LIFE CYCLE
This species of eriophyid is a cool weather pest. The
overwintering eggs hatch in early to mid-March, before
those of spruce spider mite. Poplulations of this mite
build quickly in early spring, with most eggs hatching
within the first week. In the Pennsylvania area, an
average of 24 eggs/needle have been frequently observed.
The popluations decrease in the summer and increase in
the fall before overwintering eggs are deposited in
November. Nymphs emerge from the egg headfirst and
immediately move to healthy tissue to feed, probing the
needle with their beak before inserting the chelicerae.
The mite feeds on the upper surface of the needle for a
short time and then moves to the undersurface; first
generation eggs are deposited here, and subsequent
generations are restricted to feeding on this surface.
DAMAGE
At first glance, damage caused by the Hemlock Rust Mite
appears similar to that caused by spruce spider mite. The
chlorotic spots are much smaller, however, and give the
needle a silvery appearance that is especially evident
along the outer margin of the needle. Premature needle
drop will result if the population is left unchecked. In
general, Hemlock Rust Mite can be identified by the
damage and presence of cast skins on the underside of the
needle. In winter, look for white to amber eggs along the
base of the needle, where it lies flat against the stem.
CONTROL
Eriophyid mites are not susceptible to control with the
standard miticides. Consult your county agent or local
certified arborist for materials suitable for control of
these pests.
* See Woody Ornamental Insect, Mite and Disease Management, The Pennsylvania State University (2005) for more details.
WARNING: Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of reach of children, pets and livestock. Dispose of empty containers right away , in a safe manner and place. Do not contaminate forage, streams or ponds.
For professional assistance
with tree and shrub problems,
contact Keystone Tree Experts at (215) 348-4444.
