Q&A

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,
Jeryl McComas
Irish Meadow
Ironton, Ohio

DEAR JERYL:

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 offer:

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 ladybugs.

• 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 population explosion.

Good luck,
Darrell

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