Jacky, one of the participants in the Food Gardening for Beginners e-learning program posted an interesting question to the discussion forum. She is concerned about mutilating her plants with her home-made organic insecticide.
Here's her post and my reply. Maybe this will also improve your chances when playing Russian roulette with your crops.
Jacky's Post…
Prior to the course I started up my first "mini" garden - in pots & crates - in the courtyard. All started off fabulously. I have lately been under attack by caterpillars & worms. They have virtually destroyed my lettuce, watercress, rocket, spinach, borage, etc.... I made a spray with sunlight soap, garlic, chillies & water (trying the organic approach).
I have not yet ascertained if this works, as with all the wonderful rain we are having - I can't keep up. (Not that I am complaining about the rain.) Does this solution work, or is there an alternative "organic" solution? and how much sunlight should I use, as I think I am now burning & wilting my leaves? Eish!
My Reply…
I'm not a big fan of home made spray concoctions. Not that they don't work. Most are actually somewhat effective, and at least a few have been used for many years.
My problem is that most garden gurus who recommend them haven't got the foggiest idea why they include specific ingredients and which insects they will control. We often see them hailing their recipes as 'general sprays'. This does not make sense, and neither does it work that well, as a caterpillar is simply not a snail and a snail is not an aphid.
Some gurus are not even aware that most of these sprays are actually repellants. Meaning you have to carefully cover everything you want to protect. Otherwise the insects just move to another untreated plant. And again, a repellent for one type of insect does not always work that well for another.
My last problem is that people do not think about the effects these so called safe organic sprays will have on their plants and the environment.
Your spray being a good case in point of just about all the above. So let's have a look at each ingredient you are using.
Water
The water is just a carrier for the other 'active ingredients'. So no problem here.
Dish Soap
Dish soaps are a common ingredients in home-brews for soft bodied insects such as scale, whitefly and aphids. The usual safe rate of application is 5ml - 15ml per liter water. The soap is supposed to "clean up" the soft-bodied insects by washing off the wax cuticle that surrounds their bodies. And it can be quite effective against aphids and whiteflies.
Problem is that plants have wax cuticles just like insects have. Removal of the plants wax doesn't kill it outright, as it might an insect. But it does allow water to be lost from the leaves. This leads to leaf scorch and leaf drop which will weaken the plant and can eventually result in death.
Garlic
Garlic is a repellant, and a number of insects including whiteflies, aphids and beetles will rather look for more sweet smelling pastures than those permeated by garlic. It works, plain and simple. There is one caveat though. Good coverage is essential. The stronger the concoction the better. Ideally the smell should last for more than a week. And dish soap will make the garlic spray more effective.
Problem with garlic is that you cannot use your edible crops for up to a week after they've been sprayed. Not that the garlic is harmful, you just cannot wash off the smell.
Chili Pepper
Hot peppers contain a compound called capsaicin which causes the burning sensation. And it has been shown to deter insects, though it will not necessarily kill them. In home-brews ½ to 2 cups of the hottest peppers you can find is mixed in a blender with 2 cups water. Be careful when doing this. Capsaicin can cause severe discomfort and pain when it gets on your hands and into your eyes. Even the fumes when blending can cause discomfort. The resulting liquid is strained and mixed with 1 liter of water and 1 to 2 teaspoons of dish soap. This brew is then sprayed onto the plants.
Problem is that home-brews are not always that effective as it is difficult to get a strong enough capsaicin concentration without causing some discomfort to yourself in the process. And when you do, the resulting concoction might be damaging to your plants, heightened by the addition of dish soap. One last drawback is that the capsaicin also does not "stick" to the plants long enough to have a lasting repellant effect. Meaning you have to spray more regularly.
Final Analysis
Putting it all together again, your home-brew is essentially a repellant spray which needs to be used with caution if you do not want to damage your plants. But it should be very effective against most soft bodied insects if you can get thorough coverage. It is also worth noting to always use a new home-brew recipe on a few plants first before spraying all your crops.
Solution
Get your recipe right and spray more often or buy a good quality commercial insecticide. Preferably organic. And before you roll over your eyes or gulp for air, allow me to explain. It has been proven that when used judiciously, and in a safe and responsible way, insecticides might have little or no impact on the environment. It is the large scale, irresponsible overuse that is poisoning all of us.
Also, when you are starting out, you need all the help you can get. Take a sample of the insect in a sealed zip lock bag to your local garden centre. They should have at least one knowledgeable horticulturist on their staff. (If not, find one that does.) Ask the person to identify the pest and recommend a safe control.
Key is to use insecticides that are known as 'contact' insecticides and not 'systemic' insecticides. The latter are 'absorbed' by the plant and the whole plant become poisonous to the pest. Not something you want in your food crops.
The 'contact' insecticides to consider are those that are registered for use on tomatoes. They do leave a residue though. So pay careful attention to the application rate and the safety period.
If you have any recipes to share please post them below.
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