Diseases are far more important than insect pests on tomatoes. Tomatoes grown outdoors are much less susceptible to disease than ones grown indoors. Keep a careful watch on indoor crops and treat plants immediately.
Poor drainage will cause Root Rot. The roots below ground are brown and corky; the top will wilt in hot weather. The root rot cannot be stopped once its taken hold. A mulch on top of the ground will help the formation of new roots.
Root rot can be treated if the plant is slightly affected. Treat the affected area with Cheshunt Compound. This is usually a disease of seedlings or young plants.
Stem Rot or Didymella is a disease of mature plants of which there is no effective treatment. This can be spread from plant to plant by watering or by handling. The fungus can over winter on debris or in the soil. It is essential the soil be well cleaned or sterilized before tomatoes are grown on the same area.
Tomato Blight is a devastating disease of tomatoes and is an increasing problem in some areas of the country, care must be taken to destroy all green matter to prevent a follow on infection. Wash or destroy any canes used in the growing of tomatoes with Blight. There are some new varieties which are Blight resistant which are worth trying if Blight is a continuing problem.
Unlike potatoes rolled leaves on tomatoes do not indicate disease. The curling of young leaves is usually taken as a good sign if they are dark green. The rolling of older leaves is usually due to a wide variation between day and night temperatures. Providing no pests are present no action need be taken.
Either too much heat or too little potash can cause blotchy fruit. The glasshouse can be shaded to reduce the heat, use a high potash feed. Blossom end rot, which causes the end of the tomato to turn black, is due to irregular watering when the fruit is setting and can be problem when using grow bags. To avoid this ensure a regular water supply to each plant.
Two of the main pests that attack tomatoes are Whitefly and Aphids. Both can be treated effectively either by predators or an insecticide spray. We have found predators work extremely well; they work continuously throughout the season.