Pest
Management
I. Insect and
Disease Problems
Typical insect
problems in greenhouses include whiteflies, mites, thrips, aphids and
leafminers. Typical disease problems include damping-off (Pythium
sp.), Botrytis gray mold, powdery mildew mildew, tobacco mosaic virus
and beet pseudo-yellows virus. A number of viral diseases can be vectored
by the silverleaf whitefly, including gemini viruses. The best prevention
for pseudo-yellows and gemini viruses is to exclude the vector, silverleaf
whiteflies. Disease and insect problems typical of field production such
as early blight and beet armyworms can also occur in greenhouses, however,
particularly those with open sidewalls in vegetable production areas.
II. Biological
control
A number of
beneficial insects for available for use against greenhouse pests. In
some countries, companies selling biologicals must meet quality standards
in terms of number, type, and viability of insect supplied. In the US,
there are no such restrictions on suppliers, and the purchaser needs to
carefully inspect the material received to determine its condition. If
packaging was inadequate, the beneficials may have been crushed. One technique
to determine approximate quality is to place the material in a glass jar
covered with a fine insect-exclusion screening. If the jar is kept under
good conditions for emergence, adult beneficials should be observed within
a few days. Parasitoid wasps used to control whiteflies (particularly
Eretmocerus eremicus) are very
small and difficult to observe, but their movement can generally be detected
with the naked eye. Beneficial insects tend to be more sensitive to pesticides
than pests. Once beneficials have been introduced into the greenhouse,
the types of pesticides that can be used are very restricted. Lists of
allowable pesticides are usually available from suppliers.
III.
Bio-pesticides
Biopesticides
represent a new category of products (sometimes also called biorationals
or reduced-risk pesticides) which are safer for humans and have fewer
off-target effects. The registration process for these products in the
US is streamlined compared to conventional pesticides, making them more
likely to be registered for a specialty crop such as greenhouse tomatoes.
Materials derived from Beauvaria bassiana, an entomopathogenic
fungi,. B. bassiana are available
in several formulations to control whiteflies. These materials can be
sprayed on the crop just like conventional pesticides, but like conventional
pesticides, applications must also be repeated. Insect growth regulators
and products derived from natural insecticides, such as neem oil, are
other types of biopesticides.