Sunday, April 19, 2009

Neem oil

Neem seedlings appeared in garden shops a few years back, advertised as having remarkable insect repellent properties when mashed up and used as a spray. I can't remember the details of the process, but I had my doubts that I'd ever be bothered to try it. However, I bought a couple of seedlings out of curiosity, and both died with the autumn cold.

Recently however, I read that neem oil 'may be' effective in treating powdery mildew on wolfberry plants. My wolfberries put out some very pretty green leaves this spring, many of which were promptly affected by this dusty mildew which makes the leaves shrivel and fall off. I also noticed legions of sex-crazed leaf-beetles copulating all over the shrubs, which means their horrible turd-coated offspring will soon be eating what leaves the mildew spares. I wondered if neem spray would solve both problems.

Powdery mildew on wolfberry leaves

So I found a place that sells sprays, Ide Shokai, and bought three bottles of spray. They recommend spraying every 3-4 days. I tried spraying the tops of the broad beans that were invisible for green fly, and the spray made them drop off with almost comical alacrity. Then I sprayed four wolfberry bushes, focusing especially on the mildewed parts.

Greenfly on broad beans

But I realized that already, one of the three bottles was half empty. At a rate of every 3-4 days, this method is not going to be economically (or environmentally) sustainable, however well it may work. As a slight application of scepticism, I tried spraying greenfly with plain water, and lo! they dropped off with exactly the same alacrity. It remains to be seen if the neem will actually suppress the mildew. I have tried milk and water spray in a 3-7 mix which is supposed to work, but my testing wasn't rigorous enough to tell. I could try some slightly scientific tests to see what actually works. The milk option would surely be cheaper if it actually has any effect.

Another very tempting option is just to do nothing and see if everything is still tolerably productive...

No comments: