As one of the most popular vegetables grown by home gardeners all over the country, tomatoes are the subject of many questions about diseases and their treatment. Many diseases can affect tomatoes, and although some are very serious, most are controllable with proper prevention and treatment.
The most basic technique for controlling tomato diseases and disorders is prevention. Proper soil preparation, including tilling, which kills weeds and certain insects, is important. Make sure the soil has a pH level of 6.2 to 6.8. This allows for proper nutrient uptake and utilisation. An adequate amount of fertiliser and organic materials in the soil ensures there will be no deficiencies. Crop rotation is another useful technique. Try not to grow tomatoes in the same location each year. Moving the tomato plants from one area of the garden to another the following year helps prevent disease. If disease is a problem one year, you should burn all dead plants at the end of the year and, if possible, sterilise any cages or stakes with a torch or in a fire. Also, do not smoke or use tobacco products near your tomatoes, as they are susceptible to tobacco mosaic virus which can be present in tobacco products.
Some plant varieties are disease resistant. These varieties will be designated by codes on seed packets or in descriptions in seed catalogues. Some of these codes are V, F (or FF), N, A, T, St and TSWV. "V" indicates resistance to the Verticillium family of diseases, "F or FF" denotes Fusarium oxysporum resistance, "N" refers to a resistance to nematodes, "A" stands for Alternaria, "T" indicates tobacco mosaic virus, "St" is Stemphylium or grey leaf spot, and "TSWV" is the code for tomato spotted wilt virus. Some varieties will carry resistance to one or more of these diseases. However, resistance does not mean they are immune but simply that they are less likely to submit to one of these disorders than a non-resistant variety.
Many growers mistake simple nutrient deficiencies as disease problem. If tomato plants exhibit stunted growth, yellowing leaves, leaves with green veins but yellow colouring, purplish leaf colour or tomatoes that rot on the blossom end, it's probably an indication of a nutrient deficiency and not a disease. All of these problems can be cured with proper fertilisation.
Many disease treatments are available in your local garden centre. Most tomato diseases can be held in check if a fungicide is applied at the first sign of trouble. Remove diseased leaves and stems. Tomato plants with viral disorders should be removed immediately and all tools disinfected.
Other techniques are important for disease prevention during cultivation. Avoid handling and working with plants while they are wet. Avoid top watering; try to water the plants at the soil surface. Avoid watering plants in the evening to help keep down fungal infections. Avoid handling other species such as peppers, melons and members of the nightshade family while working with tomatoes. Try not to plant tomatoes near plants of these types. Keep beds free of weeds and control pests when found, especially aphids, which may carry and transmit disease.