Leaves are sticky, yellow, and distorted

Aphids are tiny insects that come in many colors and suck plant juices from the leaves. You’ll often find them in vast colonies on succulent, new growth. Aphids excrete a sugary substance called “honeydew,” on which ants feed and on which black mold may develop. 

Leaves have tiny, shotgun-like holes in them, about 1/8 inch in diameter. 

Flea beetles are tiny black insects that hop like fleas when disturbed. They chew little holes throughout the leaf surface. 

Leaves have big, ragged holes in them, and some leaves even appear to be missing. 

A tomato hornworm is a large, green worm with white diagonal markings on its sides, and with a red or black curved “horn” at its rear. Only a few may be present but they are absolutely voracious eaters. You might come across a hornworm that has what looks like grains of rice on its back; these rice grains are actually the cocoons of the parasitic braconid wasp. When the wasps pupate, they will feed on (and eventually kill) the hornworm.  The Colorado potato beetle is a yellow, black-striped insect. Its larva is large and red, with two rows of black dots on its sides. Both the adults and larvae can severely damage plants by feeding on leaves and stems. 

Leaves are mottled and yellowing, and a puff of white insects arises if the plant is tapped. 

Whiteflies  are tiny white insects that feed on plant sap. Like aphids, they excrete “honeydew” on which black mold may grow.

 Leaves are yellow; plant is stunted and wilts in hot weather. 

Nematodes are microscopic worms that live in the soil and feed on plant roots. If you pull the plant out of the ground, you’ll notice that the roots are swollen and distorted. 

Leaves have light and dark mottling. 

Tobacco mosaic virus is very infectious and can be spread by simply brushing against plants. The virus is seed-borne, but can also be passed to the plant from tobacco in cigarettes and other products (the virus actually survives tobacco processing). 

Older, lower leaves are yellow; shoots or the whole plant wilts. 

These three diseases are difficult to tell apart. Fusarium and Verticillium wilt are caused by soil-borne fungi, and walnut wilt comes from planting your tomatoes too close to a walnut tree. The tree’s roots produce a chemical called juglone which is toxic to tomato plants.

Older leaves have dark brown, concentric rings on them.  Or, fruits have dark, leathery, sunken lesions at the point of stem attachment.

Early blight occurs in humid weather. The fungus overwinters in residue from diseased plants, and can also be present on the seed itself.

Leaves or fruit have irregular, greasy-looking or water-soaked gray areas that expand rapidly in wet weather. 

Late blight is the fungus that caused the great potato famine in Ireland from 1845-1850. It occurs most often in humid weather, during which a gray mildew grows on the undersides of the affected leaves of tomato and potato plants. 

Plant suddenly and rapidly wilts, even though the leaves are green and it has been watered regularly. 

Baterial wilt is caused by a soil-borne bacterium. It persists in the soil in the southern states, and can be found in greenhouses in the winter in northern areas.

 Circular or radial crack at the stem end of ripening fruit.  Cracks can extend deep into the fruit, causing it to rot.

 Tomatoes will crack when environmental conditions cause them to grow rapidly during ripening.  The rapid growth is frequently promoted by a drought followed by heavy rain or watering.  Cracking is more severe in hot weather.  Cracked tomatoes are edible.

A round, sunken water-soaked spot develops at the blossom end (opposite stem end).  The spot enlarges, turns brown to black and feels leathery.  Mold may also grow on the rotted surface. 

Blossom End Rot occurs from a lack of calcium in the developing fruits. The first fruits of the season are the most severely affected.  This results from slowed growth and damaged roots caused by these factors: 

1. Extreme fluctuations in soil moisture 
2. Rapid early season plant growth followed by extended dry weather. 
3.  Excessive soil salts. 
4.  Excessive rain. 
5.  Cultivating too close to the plant.  

Sunken spots occur on ripe tomatoes.  The centers of the spots darken and form rings.  Spots may merge, covering a large part of the tomato.

Anthracnose is caused by a fungus that rots ripe fruits.  Infected fruit is inedible.  Fruit on plants partially defoliated by leaf spot disease is prone to infection.  Infections frequently become epidemic in hot, rainy weather.  Water from heavy dew, over-head watering and frequent abundant rain provides the moisture necessary for infection.