Friday, July 16, 2010

Recipe Friday: Insecticidal Soaps

flea beetles and flea beetle damage on tomatillo plant

A few weeks ago I noticed tiny holes all over my tomatillo plants. I also noticed tiny black beetles that would jump away whenever I tried to pick one up. It didn't take long to put the two together. Flea beetles seem to come out of nowhere to destroy many common garden plants and are a pain to get rid of. Insecticides like rotenone and carbaryl (Sevin dust) work pretty well, but I don't like using them. This is partly because they are indiscriminate killers - honeybees, mantids and other beneficial creatures are also killed by them as well as fish and crustaceans once they reach the water supply - and also because they are harmful or toxic to me if they come in contact with my skin or if I breathe the airborne dust. The EPA lists carbaryl as a likely human carcinogen and rotenone has been linked to Parkinson's. My family history already puts me at a moderately high risk of developing neurodegenerative diseases and I don't know about you, but I would rather let the bugs have part of my garden than put more carcinogens into the water supply and on my foods than commercial farming operations do already. Enter insecticidal soaps. 

Lots of home gardeners use insecticidal soaps for many garden pests and problems. Depending on additives* used, insecticidal soaps can be used to treat everything from mildews to insect infestations to rabbits eating your greens. There are commercially available insecticidal soaps marketed for all of these uses, but they can be a bit pricey. The basic recipe is usually 2-4 tablespoons of liquid soap (most commonly dishsoap) in a gallon of water. This makes a mild soapy solution that works to suffocate aphids and mealy bugs and prevent many insects from starting to eat your plants in the first place. This is a great preventative measure, but sometimes I'm not so diligent about preventatives in the garden and find it necessary to fight dirty. This recipe uses ammonia as an additive for better and faster pest killing and will make approximately one (1) quart of insecticidal soap. 

cast of characters

1.5 cups liquid ammonia
1.5 cups water
1-2 tablespoons dishsoap


1. Measure out equal parts water and ammonia. The actual measurements do not matter so much here as long as there is equally as much of one as the other. You could make up a 5 gallon bucket of the stuff and have done with insecticidal soap needs for the whole neighborhood if you wanted. 
2. Preferably using a funnel, pour both water and ammonia into spray bottle. I used an old vanilla extract** bottle coupled with an extra spray nozzle from the dollar store. 
3. Add soap to bottle. Measuring isn't really all that necessary here, either. Just squeeze a good bit in and you'll be fine; that's what I did. Be aware that concentrations of soap much higher than a couple tablespoons per quart can and will harm vegetation so use discretion.
4. Tighten squirt nozzle on bottle and shake to combine. 
5. Label bottle and spray on all the creepy crawlies you want dead and gone on indoor or outdoor plants. For best results spray every day or alternating days. 
In my observations, the majority of pest insects tend to be most active in the evening just prior to dusk and this is when I would recommend spraying. Spraying in the evening also limits the exposure bees and other advantageous insects experience. The basic recipe or recipe with ammonia also works as a spot cleaner for kitchen and bath, but doesn't work very well on glass because of the soap. 

DIY insecticidal soap. If this doesn't work, I'll have to get really dirty and bust out the neem.

Keep in mind when using your soap spray that, no matter what the additives are, the primary insecticidal properties only apply when used as a contact killer. That is, in order for it to work it must be applied directly. Soap clings to the insects, drawing moisture out of their bodies and killing them through dehydration. This recipe uses ammonia to help in the dehydration process; basically they dry up before they can really get a chance to run away. The amount of ammonia used here will break down with
I am partial to this particular recipe because it is extremely effective in killing insects and also because it is not toxic. Dogs and other pets and children can continue to be in and around the garden during and after application and the worst that will happen is Fido decides to chow down on some sprayed spinach and throws up; though this would probably be more due to the soap than the ammonia. Ammonia is not a good thing to breathe, but because all animals but amphibians and fish have a built-in mechanism to process it out of the blood stream as a waste material, it is extremely unlikely you or your loved ones will be able to ingest or inhale enough during use to cause any damage. This does not mean that you can store it laying around where children or pets would be likely to find it. Be sure to store your insecticidal soaps out of the reach of children and pets just like you would any other household chemical! Also: DO NOT use this or anything containing ammonia in conjunction with anything containing chlorine or bleach or you will create highly poisonous gases that will harm you and your loved ones***.

*I have listed a number of additives below. Each of these has a specific purpose when added to your basic soap spray recipe. All of these, with the exception of ammonia, should be made up only as much as you can use at one time or be refrigerated/frozen for future use as they will mold.I can personally vouch for each of these additives, though their effectiveness for you may not be the same as I have experienced due to several variables including potency of raw ingredients and the extent of your particular pest problems.

Ammonia - aides in rapid dehydration of invertebrates and is what I use most often in my insecticidal soap 
Milk - used diluted in the water portion of basic recipe or to replace the water portion altogether; helps with mildew and molds, may serve to inhibit some insects
Garlic, onion and other alliums - put a handful of garlic cloves, onion pieces (can be cut off, discarded pieces) or mixture of both in a glass jar, pour in enough boiling water to cover, put a lid on it and set aside overnight to steep; repels insects and other pests, sometimes prevents damage from rabbits and other foragers including birds as well as snails and slugs
Chili pepper or hot sauce - process dried peppers or powdered pepper as garlic and alliums above or add 4-5 tablespoons of hot sauce to basic recipe; best additive for use against rabbits, deer and squirrels, not useful for birds as they lack the salivary glands necessary in order to have a reaction to the capsacin in the pepper

*Vanilla extract also makes a great insect spray. It works like an insecticidal soap in some instances, killing pests on contact, probably due to the alcohol content mostly, but the chemicals used in the creation of imitation vanilla that make it taste good to us also serve to repel many pests including aphids and flea beetles.

*** Chlorinated municipal water does not have high enough concentration to be of concern as once it had reached the consumer the vast majority of chlorine has already dissipated. Most municipal water treatment facilities are also switching from chlorine treatment to chloramine treatment.

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