DEAR NEW FARM:
I am having a problem with aphids in the greenhouse this
year. I have yellow sticky traps hanging a few inches above
the benches approximately 3 feet apart. I am also using an
insecticide for killing aphids. Since I also have herbs in
the greenhouse, I would prefer to use hot pepper wax sprays
but was wanting to know if these are just as effective. Aphids
are mainly attacking certain types of tomato plants, zinnias,
hot pepper plants and vinca. There has been a cold spell in
our area this past week, so I left the heat off, leaving the
greenhouse around 45°F-55°F at night, hoping that
would help. Any advice would be most helpful. It seems they
are nearly impossible to control once they get into the greenhouse.
I checked plants on a daily basis and started treating early,
but I still have a problem. If there are things I could have
done before and while transferring seedlings to the greenhouse,
I would appreciate any information you might have. I used
Miracle-Gro professional potting mix when planting seeds,
but I am wondering if the bags could have been contaminated?
Thank you again,
Once again, we turned to one of our colleagues with much
experience in this arena, in this case Darrell Frey of Three
Sisters Farm (www.bioshelter.com)
in western Pennsylvania. Here’s what Darrell had to
Aphid control in a greenhouse involves both long-term
strategies and quick-fix emergency solutions. At Three Sisters
Farm, we have developed an indoor ecology that keeps pest
levels low most of the year.
This system includes a number of natural controls:
- We maintain permanent plantings of nectar-producing
alyssum and other flowers in the greenhouse. Blooming
year round, alyssum provides habitat for aphid predators
such as predatory wasps, gall midge and syrphid fly as
well as for the white fly predator encarsia formosa.
These predators are active from late winter until late
fall in a heated greenhouse.
- In late fall, when the days shorten and most predators
are dormant, the insect-consuming fungus beauvaria
bassiana keeps the aphid populations under control.
While commercially available, beauvaia bassiana
occurs naturally in our greenhouse. We collect the year’s
first infected aphids each fall and culture them in a
sealed container. After several days, the fungi release
spores. These we mix with distilled water and spray on
plants susceptible to aphids. In the cool greenhouse the
fungus effectively eliminates aphids until warming days
of spring. Timely release of ladybugs or lacewing larvae
will also greatly reduce aphid populations. Since we discovered
beauvaria bassiana, we have not need to purchase
- Between the season of the fungus and that of the predators,
aphids can become established at unacceptable levels on
some plants. Not only do they suck vital juices from the
plants, they also spread viral and bacterial diseases
among plants. We have found insecticidal soap to be very
effective in reducing aphid populations. We mix the soap
with distilled water (hard water reduces its effectiveness).
Sprayed directly on the insect, it can kill them in a
minute. Several treatments may be necessary to maintain
control as aphid eggs hatch.
It is unlikely that aphids arrived in a soil mix. However
a soil mix high in soluble nitrogen could encourage aphids
due to excess nitrogen uptake in the plants. A soil mix
fertilized with compost rather than soluble chemical fertilizer
may be less likely to encourage pests.
Use of insecticides only compounds the problem because
they kill the aphid’s predators. Then aphids return
and quickly reproduce in the predator-free environment.
Sticky traps are better used as a monitor for pests rather
than a control. This is because they are more likely to
catch the flying adult aphid predators than the aphid themselves.
Aphids only have one or two flying generations a year; the
rest of the year they are wingless.
To summarize: Our organic aphid control involves a long-term
strategy of providing habitat for beneficial insects, use
of beauvaria fungus in early spring, monitoring plants for
pests and using insecticidal soap spray to control the occasional
us with comments, suggestions and questions.