Agriculture Reference
In-Depth Information
In well-managed organic orchards, predators usually control pest mite
populations effectively. Serious mite outbreaks are often caused by pesticide
programs that kill off predators, including predatory mites. It is important
to make dormant applications of lime sulfur 30 days or more before bud
swell and applications of horticultural oil during bud swell through green
tip. At those times, predatory mites are generally not in the trees and are
not harmed by the pesticides. During the growing season, sulfur fungicides
will reduce mite populations. Here, however, is one of the serious weaknesses
in organic orchard pest and disease management. The sulfur applications
needed to control serious fungal diseases are also toxic to beneficial pred-
atory mites. The overuse of sulfur fungicides during the growing season can
lead to outbreaks of pest mites. As you develop a pest and disease manage-
ment plan for your orchard, use as many strategies as you can to reduce the
number of sulfur sprays applied to the trees during the growing season.
Pearpsylla.
This serious pest was introduced into North America. The psylla
resembles a small cicada about 1/10 inch long or less and ranging from
greenish-brown to very dark, depending on the time of year. Adults over-
winter in bark crevices or on fallen leaves and emerge before bud break to
lay eggs at the base of buds.
The larvae hatch in 2 to 5 weeks and begin feeding on leaves and buds,
sucking the juices from the phloem. These larvae pass through a series of
five stages (instars) in 30 to 50 days, and there may be three to five overlap-
ping generations per year, depending on the length of the growing season.
The psylla's feeding weakens the pear trees, but far more serious damage
is done by the virus-like pathogen (phytoplasma) carried by the psylla. This
stances into the pear trees that cause shock and damage to the trees, and
the honeydew the psylla excretes contaminates the fruits and supports the
growth of sooty mold.
Fortunately, it is relatively easy to manage pear psylla. Many predators
and parasites attack pear psylla, including adult and larvae ladybird beetles
