The low chemical activity of the inert gases is due to the fact that their outermost, or valence, electron shell is complete, containing two electrons in the case of helium and eight in the remaining cases.
Often only one side of a plant is affected at first, but symptoms eventually spread. Tomato Leaf SpotâSeptoria lycopersici Fruit is not affected, although sunscald can be a problem due to foliage loss. Numerous brown spots on leaves, each about 1/16 inch in diameter. They do not have a yellow halo and they do have black specks in the center. First symptoms are usually on lower leaves after the first fruit sets.
Tomato Diseases to Treat. Several kinds of diseases can plague tomato plants. Watch leaf health, watering status, and the way that the plants are growing so that you can catch the disease early to treat or eradicate it. Blight. Two fungal diseases are known as blight - Alternaria solani or early blight, and Phytophthora infestans or late blight.