Spraying your plants with milk
won't drive bugs away from your garden, but the dairy
product can be used to culture Bacillus thuriugiensis
Berliner, a well-known bacterial pesticide sold under such
brand names as Dipel, Thuricide and Biotrol. The agent is
quite effective in controlling — among a number of
insect problems — infestations of loopers, which are those
pesky little worms (they're actually moth larvae) that
attack broccoli, cabbage, cauliflower and other members of
the cole family. Once eaten, the bacteria paralyze the
larvae's intestinal tracts and bring about their death in
two to four days.
Before you spray your garden with thuringiensis, though, be aware that this bacterial-warfare weapon is fatal to the caterpillars of all Lepidoptera (an order of insects that includes many lovely, and relatively harmless, moths and butterflies) . . . so please don't employ the remedy in cases where simply handpicking the loopers off your plants will do the job. (That rule, of course, applies to the use of any pesticide, natural or otherwise!)
Using Milk as a Pesticide
If the little green caterpillars get completely out of control, you can go to the store and buy some commercially prepared Bacillus thuringiensis (BT) and use the product in conjunction with the pests themselves to brew your own supply from that point on! The basic procedure for doing so was mologist at Louisiana State University's Cooperative Extension Service in Baton Rouge. Dr. Pollet decided that because milk is a good medium for bacterial culture (a fact that not only causes the liquid — especially when unrefrigerated — to spoil, but allows us to harvest such by-products as cheese, yogurt, and kefir), and since Dipel, Thuricide and Biotrol are all bacterial pesticides, it should be possible to use milk to extend the bacteria's useful lives.
According to a report on Dr. Pollet's work, the process goes like this: The pesticide is sprayed on the plants, where it's eaten by the loopers. Then the tiny parasites develop inside the caterpillars' bodies and kill their hosts. When the infected larvae are gathered before the bacteria in them die, and are blended into milk (an effective culture for the microorganisms), the bacteria strain will stay alive and can be used again to kill other loopers.
Experimenting With Natural Pesticides
After reading this report, I decided to conduct my own experiment: I wanted to see for myself whether the system would work. (Besides, I always jump at any chance to save money, and commercial bacterial pesticides are expensive!)
All the project involved was gathering a palm full of infected loopers from a section of my cabbage patch that had been treated with some store-bought BT . . . mashing and blending them into one pint of warm milk (I thought a lukewarm environment would promote bacterial reproduction . . . then letting the looper or milk mixture stand for three day, sure the caterpillars you start with are still fresh. Once the larvae are dried up chances are the bacilli will no longer be active.) Next, I strained the brew through cheesecloth, diluted it with water to make a gallon of liquid sprayed the concoction on some looper-infested broccoli plants.
Two days later, it was evident that the larvae were no longer eating. By the next day they were becoming discolored, and soon thereafter they were very dead. My experiment was a success!
Putting Homemade Pesticides to Use
Having once-used loopers infected with bacteria from a commercial source to make a new batch of pesticide, I wondered whether I could continue the chain by using pests that had been sprayed with my home brew (much as a starter from each batch of yogurt can be used to make additional yogurt). So I gathered a dozen loopers from the broccoli, treated with my pesticidal milk shake processed them in the same manner sprayed a second infested patch. This third generation mixture proved to be just as effective as the first and second applications had been.
And just how many times could the process be repeated? Well, I really know, but it's reasonable to expect that as long as the Bacillus thurangiensis Berliner can be kept alive — and milk to provide a ready means of doing that — the bacteria will live to serve you again and again.