Insects and diseases
Fungi such as powdery mildew,
septoria leaf spot, anthracnose, early and late blight, and fusarium and
verticillium wilt disease are most common during prolonged cool, rainy, heavily
overcast weather. To help prevent the spread of these diseases
do not work around the plants while they are damp. Water plants early in
the day. Mulch to prevent spores in soil from splashing up into plants.
Plant the tomatoes far enough apart to allow good air circulation and sunlight
exposure. Prune excess limbs for the same reason. If you can avoid it,
do not plant tomatoes in the same place year to year. Clean up thoroughly
at season's end to get rid of any diseased plant residue.
To help prevent blight and other foliar diseases I use a copper based fungicide which is 100% environmentally friendly.
Blossom-end rot is a non-infectious disease that appears as unsightly brown patches that later turn black. It often appears during a prolonged dry spell and indicates a deficiency of calcium in the soil. Water retentive mulch with some bone meal mixed in should cure the situation.
Insects I mostly try to keep harmful insects under control by attracting beneficial insects and birds. I grow lots of native plants near my garden that attract the birds and beneficial insects. It also decoys some of the harmful insects that find the native flora more to their liking than the horticultural plants. I also keep a steady water supply for the birds. If, nevertheless, insects become a problem a thuricide based insecticide should effectively control any bothersome caterpillar or tomato hornworm infestation. It will also kill cutworms which can cause serious damage to young tomato plants. Whiteflies, aphids, leafhoppers, and other stubborn insects can easily be controlled with a biological safe insect spray.
The black walnut tree is definitely opposed to diversity. It employs chemical warfare to try and prevent anything other than another walnut tree from growing in its immediate vicinity. In the plant world this type of warfare is called allelopathy and the chemical inhibitor specifically produced by the black walnut is juglone. Unfortunately tomato plants are especially sensitive to juglone. A large walnut tree even 60 feet away could have a negative impact on a tomato plants growth. Affected plants will show signs of wilting, and the leaves will turn yellow. Growth will definitely be stunted causing the plant to eventually die.
The toxic chemical is in all parts of the tree: its trunk, limbs, twigs, roots, leaves, bark, and nuts. Using free mulch of an unknown origin may not be such a good idea for it may contain shredded black walnut.