Pale green aphids can be hard to spot, so scout for them regularly.
Aphids are one of the most common pest problems because they attack everything from peppers to peaches and they like both indoor and outdoor plants. Aphid damage alone does not usually kill plants, but the little insects transmit diseases like bacterial wilt and pea enation virus as they feed. Last week one reader asked about non-toxic solutions to keep aphids away from garden plants. Luckily, if you spot aphids on your plants you have several organic options for controlling them.
Aphids can be hard to spot because they tend to hang out on the undersides of leaves. Tell tale signs you have a problem include puckered leaves and the appearance of a sticky substance on the plant's leaves called honeydew. Aphids have a tiny mouthpiece that they insert into plants' leaves in order to suck out their juices. The insects are most often pale green, but they can also be black, grey, and peach colored. Some aphids have wings, though most do not. They attack a huge range of plants, including nasturtiums, roses, peppers, eggplants, tomatoes, peach and ash trees.
Our hops get aphids every year. Before I try any of the pest control tactics below, I usually just wait a few days. Aphids are the primary food source for ladybugs and they are very good at finding them. Last summer I lost count of how many ladybugs took up residence on our hops. They cleared up the aphid problem in no time and I didn't have to lift a finger. If you find ladybugs on your plants, keep an eye out for their larvae. They remind me of tiny black and orange alligators and can eat hundreds of aphids in a single day!
If the ladybugs don't show up, try this aphid control strategy:
Aphids do not move especially fast and have very soft bodies, which makes them easy to kill by hand. If you notice aphids on a plant, your first recourse is to just squish them right on the plant. I leave the dead aphids on the plant. I like to think that this serves as a warning to other aphids who are considering eating my plants, but it is probably wishful thinking.
If the squishing method does not seem to control the problem, or if there are just too many aphids to squish, you can kill them by spraying them with a strong stream of water. I find the brass fixtures that look like a miniature fire hose nozzle make the most concentrated spray. Spray your plants all over--don't forget the undersides of the leaves--once a day for three days. This method works great, but is not advised for delicate plants like nasturitums.
Insecticidal soap spray is an organic pesticide that kills aphids by smothering them. The spray only works if it comes in contact with the aphids, so you have to really make sure you cover the whole plant (again, aiming especially for the undersides of leaves). You can find a ton of homemade insecticidal soap spray recipes online, but I think it is a safer bet to buy a soap spray intended to be used as a pesticide. Dyes, fragrances, and other substances in household soaps could kill aphids...and your plants.
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Willi Galloway writes The Gardener column. She lives in Portland, Oregon and writes about her kitchen garden on her blog DigginFood. Her first book Grow. Cook. Eat. A Food-Lovers Guide To Kitchen Gardening will be published in January 2012.
(Images: All images by Willi Galloway)