Which specific diseases are you concerned about and I ask b'c in order to answer you folks need to know whether the diseases are fungal or bacterial.

Being in MA, I'm nearby, you don't have many soilborne diseases so I would assume that your major concern would be the foliage diseases and different products would be used depending on whether bacterial or fungal.

There aren't many products that are good anti-bacterials but for fungal ones, yes.

Carolyn

Since you specifically mention copper products and Serenade I am going to assume you are talking about the common fungus-caused diseases? If not then this won't be relevant.

Yes there are preventive programs for spraying tomatoes to prevent fungus diseases and they are often discussed here. Daconil is the spray of choice as it has proven to be most effective in comparative testing. And spraying from the day of plant out and regularly weekly thereafter (as per label directions) is the method.

Once any of the pathogenic fungus has established itself on the plant, spraying becomes a matter of slowing it down rather than preventing it.

But as Carolyn pointed out, not all tomato plant diseases are caused by fungus. So you need to know what specific disease issue you are dealing with to know what product to use, when, and how.

Dave