[Cindy Wittmier]

I have a 22′ geodesic dome greenhouse with many green lacewings that have emerged and seem to be recycling on their own for the past 6 months.

My question; how do I kill aphids without harming my beneficial insects. Will diatomaceous earth kill beneficial insects? I still have a very uncontrollable aphid infestation yet have released lacewing larva by the 1000’s.

[Eric Vinje]

Hi Cindy –

Diatomaceous Earth is made from the fossilized remains of tiny freshwater algae-like creatures called diatoms. A mild abrasive, it kills insects pests, including aphids, within 48 hours of contact. It’s not a poison, but works by scoring an insect’s hide as it crawls over the powder. Unfortunately, this would include any soft-bodied lacewing larvae that may crawl through it.

To kill aphids, but not beneficial insects, we recommend providing stable, continuous suppression of pests by promoting their natural enemies. This long term approach is also the least toxic method of controlling insects.

1. Do a little reading on common insect pests of the plants you want to grow. Field scout and monitor with traps to identify pests. Learn the pest’s life cycle so that treatment can be chosen and timed to be most effective.

2. Establish a level of acceptable damage.

3. Monitor the pest situation regularly. Only when monitoring has indicated that the pest will cause unacceptable damage should treatment be considered.

4. If pest populations are high, use a least-toxic, short-lived organic pesticide (Safer® Soap is a favorite!) to establish control while reducing damage to pest predators and the environment. Spot spray problem areas, especially new growth, and stay vigilant. Eventually your lacewing population will gain the upper hand.

Hope it helps!

[Maxen]

Try using these methods:
*Try spraying cold water on the leaves; sometimes all aphids need is a cool blast to dislodge them. Typically they are unable to find their way back to the same plant.
*If you have a large aphid invasion, dust plants with flour. It constipates the pests.
*Neem oil, insecticidal soaps, and horticultural oils are effective against aphids. Be sure to follow the application instructions provided on the packaging.
*You can often get rid of aphids by wiping or spraying the leaves of the plant with a mild solution of water and a few drops of dish soap. Soapy water should be reapplied every 2-3 days for 2 weeks.
*One variation of this soap-water mix includes cayenne pepper: Stir together 1-quart water, 1 tsp liquid dish soap, and a pinch of cayenne pepper. Do not dilute before spraying on plants.
Cheers!

[Author]

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