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I use an appropriate concentration of Neem oil mixed with bT in the form of Thuricide (after researching and finding consensus that they do mix). I use a nice four gallon back pack sprayer because it was a hell of a burden to haul 3 changes of 2 gallon bucket up and down, up and down from the farm to the garage.

In the beginning of the grow season I inserted a rod of copper into each of the plant stems of the larger tomato plants. It helped to prevent all diseases but I forgot to insert copper rods into the smaller plants as they grew larger, and it does appear that those are the plants that are falling victim first.

Science.