Peppers (Capsicum spp.) include hot, mild and sweet varieties. While they're usually grown as annuals, they're technically perennials in U.S. Department of Agriculture plant hardiness zones 9 through 11. All types have similar growing requirements, though sweet peppers are more prone to diseases and require more diligence to grow to perfection. Though many of the diseases that affect peppers can be remedied with chemicals, a natural approach to prevention can build resistance by cultivating the health of the plants. In general, if growing conditions are optimal, the chances of disease are low.
The first defense against disease in peppers is to create the best possible soil conditions. Peppers like a soil rich in organic matter with a pH between 5.8 and 6.6. Peppers are not highly demanding of nitrogen and other nutrients, but will perform poorly in sandy, infertile soils if you don't fertilize regularly. It is also important to not over-fertilize peppers with nitrogen-rich fertilizers. Too much nitrogen can lead to excessively lush vegetative growth that is weak and likely to be attacked by pests, many of which spread diseases.
Peppers need a continual supply of moisture throughout the growing season. Avoid overhead watering because wet leaves encourage many different pepper diseases. Instead, use a drip irrigation system to water pepper plants. Good drainage is also important. In waterlogged soils, growth will be weak, which also encourages disease. If you have heavy clay soil, plant your peppers in raised beds enriched with compost.
Resistance to disease is as much a genetic trait as it is a matter of growing conditions. Choose resistant cultivars, including "Aristotle," "Vidi," "Hunter," "Admiral" and "Revolution," which resist the most common pepper diseases. Planting these or other disease-resistant varieties in optimal growing conditions will help prevent most disease problems.
Pathogens affecting peppers will naturally build up in the soil where they are grown. The longer you grow peppers in the same area, the greater the disease pressure will be and total immunity will become unlikely, even if growing conditions are optimal. For this reason, do not grow peppers in the same place in consecutive years. If possible, wait four years before you plant peppers in the same spot in the garden. Because peppers are closely related to tomatoes (Lycopersicon esculentum), eggplants (Solanum melongena) and potatoes (Solamum tuberosum), and share many of the same pests and diseases, it is best that none of these crops be planted the year after or before peppers.