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Managing Pests in Small Greenhouses
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Greenhouses are great places for plant pests,
too! -
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Summary:
Greenhouses create very favorable growing
conditions for both plants
and for plant
pests like aphids, spider mites and
fungus gnats. Pests can increase rapidly and
become extremely destructive. Learn ways to combat
these insect and mite pests using least-toxic,
often even certified-organic, methods.
Jack DeAngelis, PhD
OSU Ext. Entomologist
(ret.)
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Greenhouses protect plants
from extremes of temperature and humidity, some provide supplemental lighting,
and a few even employ specialized irrigation systems. However, these same ideal
growing conditions also allow the insects and mites that can damage greenhouse
plants to thrive. In addition, greenhouses screen plant pests from regulation by
natural enemies that would otherwise keep them in check. Pests and pest damage can therefore grow rapidly
along with the greenhouse plants.
Plants growing in greenhouses have a
number of additional pest problems that plants growing outdoors generally
avoid. Chief among these are certain plant diseases, as well as insect pests
like aphids, fungus gnats, thrips, and, perhaps the most damaging of
all, spider mites. Fortunately
most of these pests can be managed using low toxicity, often certified-organic,
methods if problems are caught
early.
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an adult fungus gnat - an
important but often overlooked greenhouse
pest
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Steps to better greenhouse pest control
(1) Scout
for pests at least weekly starting as soon as
plants begin to grow. You don't need to inspect
every plant but you should develop a systematic
plan to thoroughly inspect a few plants from
different areas and record
any "suspicious activity". Better yet, take
a photo of anything that looks like it
might be a problem for later reference.
(2) Restore the natural
enemies to the system by releasing
specific predators and parasites against your
primary pests, this is called augmentative
biological control. The
exact type of natural enemy you need will depend
on your particular mix of plants so be sure to
do a little homework and check package
instructions carefully. An excellent, in depth
resource is this manual
from Penn State University.
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(3) The
next step is to use least-toxic, biorational insecticides to clean up hot
spots without disrupting the natural enemy system you deployed in step 2. The
best choices in this category are insecticidal soap and/or products that contain neem oil. Both materials are certified organic on many
crops but be sure to check your particular crop in this regard before use.
Both will control most soft-bodied pests like aphids, thrips, spider mites and
scale crawlers and are virtually non-toxic to you, your plants and any
beneficial insects/mites that you release, if used properly.
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