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.
Problems on tomato leaves ... Problems on tomato stems ... Other tomato problems ... Tomato diseases: how to identify, control, and prevent them ... Blossom end rot: how to identify, control, and prevent it ... Tomato pests: how to identify, control, and prevent them 1  ... Plant healthy, disease-free plants. 2  Stake plants to allow good air circulation to fruit. 3  Water at the base of plants. 4  Overhead water spreads disease easily. 5  Water in the morning or midday to minimize the amount of time fruit is wet.