My family loves broccoli and cabbage, so we grow them year-round. I know were in a minority with this practice, as the suppliers stop producing punnets of broccoli seedlings as soon as we get to November all my summer plants have to be grown from seed. It seems that people are put off growing these healthy cruciferous vegies by the dreaded cabbage white butterfly.
Bacillus thuringiensis is the answer. Commonly sold as Dipel, this natural bacterium has been used to control pest caterpillars since the 1950s. Everyone thought that they knew how it worked the bacteria infect the gut of caterpillars, where they produce crystals that make holes in the intestine. The infection spreads to the blood of the caterpillars and/or the grub starves to death. That was the theory.
New research into B. thuringiensis has proved this theory wrong. When caterpillars are dosed with Dipel after having all their natural gut bacteria wiped out by antibiotics, the B. thuringiensis has no effect at all. The caterpillars go on munching and growing as though nothing has happened.
Now theres a new theory. Researchers believe that the crystals produced by B. thuringiensis only make holes in the caterpillar gut. It is the other natural bacteria in the gut, such as E. coli, which cause the lethal infections. Understanding this, we can adjust our gardening practices to encourage E. coli. Perhaps making weak liquid manure and sprinkling it on the foliage of caterpillar infested plants before spraying with Dipel will increase the lethality? I wonder if the liquid from a worm farm would have the same effect?
Ill give it a go this year. Trying new techniques is one of the most rewarding aspects of gardening for me. We all have the opportunity, in however small a way, of increasing the sum of human knowledge.
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