need alot more info
plants grown, "blight" species, etc etc

just tomatoes and a few peppers it does not bother the peppers,early blight like all the photos you se on line search,when It comes I hit it with a all purpose fungicide which slows it down,I dont want to get it in the first place,it dosent start until I get 3 or 4 days of 95 percent humidty
gene

gene,
The answer to your question is, yes. Whenever a gardener is dealing with a known annual fungus/blight problem begin treatment early before the plants show any signs of infection.
By the way....are you power washing the interior of your greenhouse with Clorox added to the water when you open it up every spring? Greenhouse sanitation is important.

yes,but every year for the past 5 years Id get the bloddy thing,this year ill start on the first humid day
thanks
gene

have you tried Coir/pine bark mixes?
I've seen good results in crops that were normally fungi-susceptible in peat based media.

just a thought.

Where do you get your plants/seeds? Do you smoke? Are you sure they're not dampening off? Why don't you find resistant varieties?

I grow winter crops. The humidity can be astounding in my g'houses, but I've never had an early blight problem on my tomatoes and I don't use fungicides, ever, on food products. Start with a clean g'house, new potting mix, clean hands, fresh seed. Vent on sunny days. Watch your watering.

theres only one called legend,I think this is the first year,seeds from hydro-gardens, match and trust, dont smoke,
gene