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.
Damage to tomato plants can occur when tomatoes are exposed to chemicals such as herbicides, insecticides, or fungicides. The improper use of pesticides can lead to injury, so be sure to read label directions. Tomatoes are especially sensitive to herbicides such as 2,4-D, a common growth regulator herbicide.