Insect sprays

I was exchanging a few ideas about how to make sprays to deter insects on Twitter and thought I would add a bit to it.

Last year we had a plague of black flies that ate the broad beans and early runners.  We had been buying an organic spray that really helped to keep the numbers down.  I mentioned that to my (Yorkshire) Dad and he commented that I was wasting my money as I could make it at home.

The main thing is to make a “stock” solution that you dilute and spray with one of those £1 spray guns from Homebase or a Pound shop.  The basics of the stock are water and detergent.  The idea being that the detergent interferes with the insects breathing – spiracles.

I did some digging on the internet and found some other sprays – two main ones seem to be popular – garlic and chilli.  The recipes are all fairly similar – blend up chilli and/or garlic with some oil, water and detergent – quantities varied but not too much detergent.  However, it does look like you should be careful to use mineral oil and soap flakes.  I have to admit that I didn’t – a little washing up liquid and a few millilitres of olive oil instead.

I left blended pulp on a sunny windowsill for a week then filtered using a coffee filter into a stock bottle.  We diluted it 1:10 and sprayed on everything at the allotment for a couple of months until the plants had got properly going and could cope with a few bugs.  The chilli spray also seemed to deter slugs as well as insects. You do have to spray quite often if you have a black fly plague though.

At the end of the season, one of the old timers gave us another idea that we have to try this year.  He used rhubarb leaves instead of chilli.  Rhubarb leaves contain oxalic acid which is a powerful insecticide (and poison).

Rhubarb Spray

  • 1 cup rhubarb leaves
  • 6.5 cups water
  • ¼ cup liquid dish detergent or soap flakes
  • 1 large pot
  • A spray bottle

Step 1: Place the rhubarb leaves in the pot and cover them with the water

Step 2: Boil the water and leaves for 20 to 30 minutes. Then remove the pot from the heat and let the contents cool.

Step 3: Strain the resulting liquid into a spray bottle. Dispose of the boiled leaves.

Step 4: Add the dish detergent and mix the liquid well.

Step 5: Spray the resulting liquid on your plants to kill aphids and other disruptive insects. However, do not use rhubarb spray on food bearing plants. The poison will break down quickly, but there is still a risk that the sprayed food will have oxalic acid on them. ONLY use on things like beans, peas etc – things you will shell pop or peel!

Step 6: The rhubarb spray will rot, so use it quickly or freeze the mixture to store it. If you store it, be sure to accurately label it as poison.



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