Safer's Caterpillar Spray is, I believe, most commonly found, but I had to purchase another product. As long as it contains Bacillus thuringiensis (usually subspecies... karsaki? I can't remember) then that's one of the good products. Another good subspecies, what's found in Mosquito Dunks, is Bacillus thuringiensis israelensis.
Epsom provides magnesium and sulfur, needs to be used sparingly in my opinion (the box directions are outrageous to me) as either a foliar or root feed. Root feeding can usually safely go as high as 1tsp per gallon, but I really prefer to go low and slow, as one Ohsogreen has always reminded me, and typically start at 1/4tsp per gallon.
Seaweed extract is like a complete nutrition pie. Any time is a good time for pie, and any time is a good time for seaweed extracts. Meals, too, though you either need to make a tea with them or top-dress. Seaweed can offer many micronutrients that may not be found in other products you're using.
It *is* possible to go too strong with certain seaweed or kelp products, so watch the plants. Applied as foliar sprays it can help with disease resistance, though it needs to be applied on a very regular basis (weekly or possibly more often). When using as a foliar, I typically begin at quarter strength of the recommended dosage on the bottle, even if it has foliar strength directions IF those directions say to use it at the same strength as root feed.
In other words, it always pays to go easy and observe the plants before you make changes. I think that's the most difficult thing, learning to read the plants. Just like with every other organism, if you think about it.
