PINE ERIOPHYID - Washington State University

Extension Bulletin 1639E
PINE ERIOPHYID
insect answers
Eriophyid mites (Fig. 1) are minute, soft-bodied mites
that are spindle-shaped or wormlike in appearance.
The bodies usually have definite annulations or rings.
Eriophyid mites have only two pair of legs, which
are situated behind the mouthparts. Most adult mites
have four pair of legs. Eriophyids are extremely tiny
and can only be seen clearly with a dissecting microscope.
If you know what you are looking for, you can
just detect their presence if you have “good eyes”
and a hand lens.
Identification
Eriophyids are exclusively plant feeders and are host
specific. Some species feed on a single host species,
while others feed on a few closely related plants. They
attack all parts of the host plant, although the plant
parts attacked (buds, leaves, shoots, stems, etc.) differ
with mite species. Some eriophyids are known
vectors of mosaic viruses. The damage, characteristic
for each mite species, is often used along with
Fig. 1. Typical eriophyid mites (From USDA
Agric. Handbook 573).
host species to identify the eriophyid species. Among
the various forms of eriophyid damage are galls, rusts,
bud formations, witches’-broom, russeting, and
erineum (hairy patches of varying density or shape).
These symptoms represent localized growth reactions
of the host plants to mite feeding. Even though eriophyid
mite damage is characteristic on each host, you
need to confirm mite presence, since similar symptoms
may result from other organisms or causes.
Scientists have identified more than 1000 eriophyid
mite species. However, little is known of their biology,
behavior, or interaction with other organisms.
This is particularly true of a complex of eriophyids
in the genus Triseticus, known locally as pine eriophyids.
At least one species (perhaps two) of
Triseticus has become a serious pest of shore or lodgepole
pine (Pinus contorta). These mites overwinter
on the host tree. In the spring, right after candle elongation,
they begin to migrate to newly developing
needles, where they take up residence within the
needle sheaths and begin to feed.
Damage
Two types of damage occur on needles in the spring:
yellowing and stunting of new needles (Fig. 2), or yellowing
and curling of more developed needles (Fig. 3)
on new shoots. Typically, the affected needles later turn
brown, die, and drop from the shoot, leaving naked
branch tips. These may be symptoms of two different
species of eriophyids or symptoms of the same species
attacking the needles at different stages of growth.
If this damage spreads over much of the canopy, the
tree will spoil the looks of the landscape.

Fig. 2. Eriophyid mite damage to shore pine
needles early in needle development.
Control
Properly timed chemical sprays will satisfactorily
control these mites. Begin control measures when new
candles (Fig. 4) are fully elongated, and new needles
are 1 /2 to 1 inch long. Make at least two applications
7 days apart. Sevin is the preferred material. Sevin
will not perform well without adding 0.5% Superior
oil to the insecticide/water mix.
Commercial applicators. Use 1 pound active ingredient
(carbaryl) plus 64 ounces Superior oil in 100
gallons of water.
Homeowners. Use labels for Sevin registered for
trees or ornamentals. Add 3.5 teaspoons of Superior
oil to the amount of insecticide for each gallon of
water.
NOTE: Do not apply Sevin (carbaryl) where it may
drift onto blooming shrubs, flowers, or weeds, including
lawn weeds. Cover blooming plants and mow off
weed flowers a day or two prior to application. This
material is extremely toxic to foraging bees.
Fig. 3. Damage on more fully developed needles.
Note: damage is on bottom twig. Top twig is
healthy, uninfested. (Byther photo)
Fig. 4. Approximate stage of candle and needle
development when first application should be
made.
By Arthur L. Antonelli, Extension entomologist, Washington State University Puyallup Research and Extension Center.
Use pesticides with care. Apply them only to plants, animals. or sites listed on the label. When mixing and applying pesticides, follow all
label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are
spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of
the reach of children, pets, and livestock.
Issued by Washington State Cooperative and the U.S. Department of Agriculture in furtherance of the Acts of May 8, and June 30, 1914.
Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding
race, sex, religion, age, color, creed, national or ethnic origin; physical, mental or sensory disability; marital status, sexual orientation,
and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local Cooperative Extension
office. Trade names have been used to simplify information; no endorsement is intended. Published February 1992. Revised March 2003.
Subject code 352.
EB1639E