I Have Aphids!

I came out to harvest some mustard greens for dinner the other night and found this:

Yuck yuck yuck!

A quick google search told me that these are gray aphids, which have a predilection for brassicas. (As a side note, I’m wondering if this is what was causing the damage to the lime tree last year.)

I am both disgusted and proud – it feels like a rite of passage. I have grown brassicas that are appealing enough for aphids to patronize!

I pulled off as many of the affected leaves as I could, and then I found a bottle of Safer EndALL Insect Killer in the garage.

It said it was for organic gardening, and would work against aphids, so I decided to give it a try. The active ingredients in EndALL are:

Potassium Salts of Fatty Acids ….. 1.000%
Extract of Neem Oil ….. 0.900%
Pyrethrins ….. 0.012%

I’ve heard of neem oil, but I wasn’t too sure about the other two ingredients, so I looked them up on NPIC’s website (National Pesticide Information Center).

Potassium salts of fatty acids are also known as “insecticidal soap.” It’s essentially just soap.

The Chemistry of Soap – Wild Earth Apothecary
This is an example of a sodium salt, which is a hard soap. Change the Na to K, and you get a potassium salt, which is a soft soap.
Image source: Wild Earth Apothecary

According to NPIC, when the soap is in direct contact with the pest, it disrupts the cell membranes and cause the pest to desiccate and die (although some websites say the exact mechanism is not totally understood). The insecticidal properties of the soap are determined by the length of the fatty acid, the concentration of soap in the product you’re using, and the other active or inactive ingredients in the product. Potassium salts are most active against soft-bodied insects, such as aphids, and are non-toxic to humans, birds, mammals, and other vertebrates. However, they are toxic to fish and aquatic invertebrates.

Neem oil is derived from the seed of the neem tree. There are a few components to neem oil, and so it has a few different mechanisms of action as an insecticide. It acts as a repellent, interferes with the insects’ reproductive systems, and makes it difficult for insects to eat.

Neem Tree
Image from: The Tree Center

Similar to insecticidal soap, it is basically harmless to humans and most animals, but is toxic to fish and aquatic invertebrates. Also, it is unlikely to hurt bees or pollinators because the insect has to ingest the neem oil in order for it to work.

Lastly, EndALL contains pyrethrins, which are derived from chrysanthemum flowers. They act on the nervous system of insects and cause paralysis and then death. Pyrethrins are relatively safe for humans, mammals, and birds. (Pyrethrins are often used in lice shampoo.) However, they are toxic to fish and also to bees.

After all that research, I feel generally comfortable using a product like EndALL (there are probably things in my bathroom that have scarier MSDS’s than this product), but it would be probably be better if I used a more targeted product or no product at all. I’m guessing an insecticidal soap alone would probably have done the trick, without the pyrethrin and neem oil, but I don’t know. I’ve heard some people claim that you should just leave the aphids because they will attract natural aphid predators (like ladybugs and certain birds), but…I’m not so sure about that…there were a lot of aphids on the mustard greens.

Once I get to Portland, I’ll invest in some row cover. That seems to have done the trick for Jami at An Oregon Cottage with her brassicas without any need for any kind of insecticide.