Do you know of any organic alternative to BT (bacillus thuringensis) for the control of leaf miner on salad herbs like roquette, mustards and chards?
What conditions are favourable or not to its life cycle, and could be used
as a preventive method?
BT (bacillus thuringiensis) is a form a biological control widely used by organic growers all over the world. It is a 'tummy bug' for caterpillars (larvae of butterflies and moths) and doesn't affect other organisms. It's naturally occurring. Because of its selective action, its potential to be mass produced and be used in a very similar fashion as conventional pesticides it became quite popular not only for organic growers but also as a tool of Integrated Pest Management. Unfortunately the BT toxin is now used in genetic engineering as a gene to be transferred into all kinds of crop plants causing ecological havoc and threatening the long therm efficiency of BT as well. This is why it may have appeared in the media as a problematic tool. It is the application and use the BT genes in genetic engineering which are the problem, not the traditional BT itself. Secondly, leaf miner is not a caterpillar pest, therefore BT wouldn't work anyway. Sprinkling of woodashes on the leaves of threatened crop as a preventative methods can help keep the pest away. If infestations are already severe a Pyrethrum spray will be effective (spray at dusk , repeat after one week), or a spray of Neem soap (available from trade aid shops, a teaspoon of gratings dissolved in litre of water, spray every week).
Note from a reader:
We use a biodynamic spray with great success but it must be used in conjunction with other BD sprays. It is extremely effective against a range of chewing insects including slugs, snails, and white butterfly caterpillers and some other unidentified bugs.