Wednesday, May 13, 2009

Aphids and homemade insecticidal soap

Early this morning before heading off to work, I stepped out to the garden to have a look at the peas.

I noticed some little green specks on some of the leaves and pea pods. Upon closer examination, I discovered that they're pea aphids. Oh, no!

ABOUT APHIDS
Aphids, or plant lice, are small, soft-bodied insects which are common pests of vegetables, field crops, and fruit trees. There are hundreds of different species of aphids, some of which attack only one host plant, while others attack numerous hosts. Most aphids are about 1/10 inch long, and though commonly green and black, they may be gray, brown, pink, red, yellow, or lavender. A characteristic common to all species is the presence of two tubes, called cornicles, on the back ends of their bodies. The cornicles secrete defensive chemicals. In some species the tubes are quite long, while in others they are very short and difficult to see.

Aphids feed in clusters and generally prefer new, succulent shoots or young leaves. They feed by sucking up plant juices through a food channel in their beaks. At the same time, they inject their saliva into the host plant.

Small aphid infestations are usually not harmful to plants, but higher aphid populations cause leaf curl, wilting, stunting of shoot growth, and delay in production of flowers and fruit, as well as a general decline in plant health. Some aphids also carry plant diseases, which they transmit in the feeding process.

A distinctive feature of aphids is the production of honeydew. Honeydew is a clear, sticky dropping (i.e. poop) that lands on the leaves or anything below the plant or tree that aphids are feeding upon. A sticky glaze of honeydew may collect on lower leaves, outdoor furniture, cars, and other objects below aphid feeding sites. Honeydew coated objects soon become covered by one or more black or brown fungi known as sooty molds. Crusts of sooty mold are unsightly on man-made objects, and they interfere with photosynthesis in leaves.

Colonies of aphids are sometimes protected by certain ants. In return for this protection the ants are allowed to collect the sweet honeydew. In most cases, the ants protect aphids that have already established themselves on the plant and these aphids or their eggs and keep them through the winter in their nests. In spring, the ants transport these aphids to food plants where they protect them from enemies and transfer the aphids to new feeding sites.

In other words, if you spot ants in your garden, that could be a sign that there are aphids present, too. I have noticed ants in our garden.

HOW TO CONTROL APHIDS
While there are some insects that will eat aphids (ladybugs and parasitic wasps, for example), by the time you notice an aphid infestation, it's probably too late to try to introduce aphid predators in the hopes of controlling the aphids.

Many people try using Sevin dust (Carbaryl), thinking this chemical will do the job to eliminate the aphids. It wont. Neither will the liquid form of Sevin. Aphids fall under the category of insects that suck sap, and Sevin is designed to work on insects that chew. So, save the Sevin for the caterpillars and other chewing pests you find in your garden, if you are intent on using it.

Controlling aphids is actually easy, though somewhat time consuming. A sharp stream of water will knock the little buggers off the plant, although a hose nozzle may be too strong - especially for tender plants like peas.

Another effective alternative is insecticidal soap. The soap washes off the aphid’s protective waxy coating and causes dehydration, thus killing the insect. Insecticidal soap spray is economical, nontoxic, and environmentally safe both indoors and in the garden.

You can buy insecticidal soap mixtures, or you can make your own.

You'll need a bar of REAL soap, not detergent. Examples of real soap are Ivory soap (it floats because of all the air whipped in not purety), Fels-Naptha laundry soap (you can find these bars in many grocery stores, near the powdered and liquid laundry detergents), Dr. Bronners soap, and most all castile soaps.

If it does NOT say "soap," - if it says "beauty bar," "cleanser," "antibacterial," "detergent" or anything like that - do not use it. In recent years soap manufacturers have added degreasers and antibacterial ingredients to their products. These are VERY harmful to your plants and most likely will burn or kill them.

HOMEMADE INSECTICIDAL SOAP CONCENTRATE
1/4 cup grated soap (I use Fels-Naptha, but Ivory or other real soap - see above - will work)
4 cups hot water

Stir soap into water until dissolved. Store in a jar until ready to use.

To dilute for plant use:
Add 1 tsp. concentrate per 4 cups (32 oz.) of water. Pour solution into a spray bottle.
This soap is a contact poison - spray directily onto the aphids. It will not harm your plants.

4 comments:

  1. I like the picture of the ants protecting the aphids. Thanks for the aphid tutorial - I'll make some soap soon.

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  2. We are a couple months behind you in our gardening here in Washington State. I put a link on my blog to your site, regarding this post, because I thought it was so well explained. Thank you!

    I have gardened for many years, but you continue to educate me on why I do many of the things I do.

    I really enjoy your blog and have you on RSS feed.

    ReplyDelete
  3. This is great! I've got some F-N soap already, which I use to make my own laundry detergent. :) This'll definitely come in handy for the garden.

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  4. Hmmm. This is very helpful. I have something chewing on my potatoes and my collards, although not, curiously, on my peas. Does the insecticidal soap work generally on pests or just on aphids? And might it still be aphids even though it's not on the peas?

    Thanks!

    ReplyDelete

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