Tomato plants are an easy-to-grow crop as long as everything goes well and I'm talking about the weather. Rain, draught, heat, cold and wind are all factors in the good and poor production of tomatoes. Too much rain causes a condition known as shoulder damage-circular spots on the top of the tomato. Wind causes cat face that produces a hole in the bottom as well as sand pitting. Extreme temperature changes from very hot to very cool causes cracking and splitting. Blossom drop is caused by temperatures at 50 degrees or below at night and gray mold makes its appearance when daytime temperatures are at 70 or below, especially when it rains.
Gray mold has no effective treatment for curing the problem so your plants will eventually wilt, then die. These affected plants should be destroyed and not composted, as the problem will spread from year to year. This is yet another good reason to never plant tomato plants in the same place each year. Cold temperatures cause stunted growth, wilting and pitting, necrosis of foliage and make plant more susceptible to diseases. If your plants have a purple tone or the leaf veins are purple they are probably deficient in phosphorus. Look for high phosphorus fertilizers at your garden centers to help combat this problem.
One of the best ways to prevent these dry/moist/heat/cold problems is to start your gardening with a top layer of black plastic mulch. The plastic helps maintain an even, constant moisture as well as trapping in the heat around the root system, even when temperatures fall. Simply prepare your soil first then top off with the black plastic. In order to keep the wind from blowing it away, use your shovel to push all of the sides into the ground. When it is time to plant your tomatoes, peppers, cucumbers, squash, etc. cut an "X" in the plastic and place in your plants. This method also keeps most of the weeds away.