The following tips can help minimize disease development in tomatoes grown in your garden, field or in high tunnels:
1. Maintain optimum crop growth by providing adequate nutrients and soil moisture. Plants will grow healthy and are less prone to suffer from disease and insects. Avoid periods of little or too much water. One technique to monitor soil moisture is to use a tensiometer. A tensiometer measures soil moisture tension in centibars (cb). The drier the soil becomes the higher the centibar reading from the tensiometer. Generally, for tomatoes, the soil moisture tension should be maintained between 10-20 centibars. When soil moisture tension exceeds 20 centibars, irrigation should occur.
2. Use raised beds covered with plastic mulch and drip irrigation tape buried beneath each bed. This increases soil temperature providing earlier crop maturity, higher yields, increased quality, improved disease and insect resistance, and more efficient water and fertilizer use.
3. If possible, use wider plant spacing and remove suckers to increase air circulation. All of the foliar fungal diseases are favored by high relative humidity (> 85%) in the tomato canopy. Thus, the length of time above 90 percent relative humidity should be limited.
4. Choose a sunny location for your tomatoes. Leaf disease problems are less likely in a sunny location rather than in a semi-shady one.
5. Control weeds, particularly horse nettle and other species in the Solanum genus, in and around the edge of the garden, field or high tunnel.
6. Do not over fertilize. Vegetative growth can occur at the expense of fruit production or quality. Over-fertilization may result in higher incidence of certain diseases (e.g., early blight), increases in pests (e.g., two-spotted spider mites, aphids, thrips), pressure and with excessive salt buildup in the soil, over time.
7. Practicing good sanitation is critical. Always remove diseased tomato plants or plant parts, sterilize plant stakes prior to re-use, and clean tools and implements frequently to prevent transporting problems between fields.
Keep in mind that some diseases are difficult to manage once they become established. However, if diseases are identified early in the epidemic and all of the appropriate cultural tactics have been employed, fungicides or bactericides can be applied to reduce disease spread.