Hi Bubsky and welcome to GoY. Are you growing your tomatoes in a greenhouse or outside? If outside do you make sure you grow them on a different piece of ground each year and not where you grew them or potatoes the year before? In the greenhouse make sure there is plenty of air flowing through and don't reuse your compost from one year to the next.

1.Avoid watering with a sprinkler. The splashing water can spread the spores that cause blight. It is always best to bottom water.

2.Remove bottom leaves that come in contact with the ground.

3.Remove any leaves that may seem infected or discolored. These can hold the spores that cause blight.

4.Rotate your tomato planting spot. Only plant tomatoes in the same spot once every three to four years if possible. The disease sometimes remains in the soil and affect new plants.

5.Remove and dispose of the tomato vines and tomato waste and roots at the end of the growing season blight can over-winter in your garden from the infected plants.

We are an all organic farm so when we have blight we make the following solution and spray it on the leaves.

1 gallon water
3 tablespoons baking soda
1 teaspoon dishwashing liquid

Mix in a sprayer and apply to the leaves, treating the plants every one to two weeks.

I must say once you have blight it is difficult to get rid of but hopefully some of my information will help you.