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University
of Rhode Island GreenShare Factsheets
Taxus
Mealybug
Dysmicoccus wistariae
Homoptera: Pseudococcidae
The most common and readily noticed sign of taxus mealybug
presence on the yew is sparse yellow foliage covered with sooty
mold. The taxus mealybug occurs on stems and branches, and
tends to cluster in the forks of branches. They overwinter
as nymphs, which become active in the latter half of May; by
early summer adult females begin giving birth to live young.
There are two or three generations per year. The taxus mealybug
has been reported on other plants such as apple, cedar, linden
and maple, but is not known to reproduce on these plants.
In general, controls will be more effective if the mealybug
population on a plant is first physically reduced by pruning
out heavily infested and sickly branches. In some cases, large
mealybugs can be scrubbed off with a brush. Horticultural oil
sprays kill primarily by smothering, so they will be less effective
against mealybugs crowded together or occurring in layers on
the plant. Horticultural oil sprays kill all stages of mealybugs
that are present at the time of application. Most trees and
shrubs can tolerate application of light (summer) oil even
during the summer months. Refer to the product label for guidelines
on plant sensitivity and any temperature restrictions. Oil
products labeled as summer, superior or Volck oil are of the
highest grade and may be used on tolerant plants during either
the growing season or the dormant season, but at different
spray concentrations.
Insecticidal soaps provide another alternative. They
are effective against both active and settled crawlers. Oils
and soaps are relatively non-toxic and are especially good
choices for areas where people are present soon after treatment.
Because of their short residual life, they help to conserve
beneficial species.
An alternative to oil or soap sprays are contact insecticides
applied during the growing season when the crawler stages of
the mealybugs are present. The presence of crawlers can sometimes
be determined by sharply tapping an infested twig or branch
over a white paper. Crawlers may be orange, brown or purple,
and appear as moving specks of dust. Because of their waxy
protective covering, other stages of mealybugs are not readily
controlled by contact insecticides. Contact insecticide sprays
will not reach crawlers that have settled under old scales.
Most garden centers carry a number of insecticides registered
for mealybug control. Although resistance to insecticides may
occur in some cases, failure of contact sprays is more often
the result of not timing the applications to coincide with
crawler activity. Thus, horticultural oils are often the most
effective control. In all cases, thorough spray coverage is
essential for good control.
Adapted from Lee Townsend,
University of Kentucky College of Agriculture, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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