Choose the right crop variety for your area. A stressed plant will be susceptible to pest and disease. Keep plant growing healthy. Some varieties are more pest and disease resistant than others. Pests prefer certain varieties over others.
Some plants produce chemicals that deter the pest.
Do not plant the same crop in the same plot season after season. Soil-borne pests and diseases will increase. If possible grow crops out of season to try to avoid pests. Avoid overhead watering if possible to prevent fungal diseases. Use drip or flood irrigation.