Rotating Vegetable Crops to Prevent Diseases

By Robert Morris

Prepared for ACDI/VOCA on March 10, 2009

Rotating fields to different crops each year is one of the most important and easily implemented disease control strategies for farmers. This practice avoids the buildup of many plant diseases in the soil. The longer the rotation before coming back to the crop, the less likely a disease will occur. 

Because diseases usually attack members of the same plant family, it is best to avoid planting crops after each other that belong to the same family. Insect damage may increase when the same crop is planted in the same area over several years as well. Here are some common vegetables and the families they belong to.

• Tomato Family: Tomato, potato, eggplant, peppers
• Cucumber Family: Cucumber, melons, squash, pumpkin, gourd
• Lettuce Family: Lettuce, endive, salsify, Jerusalem artichoke
• Onion Family: Onion, garlic, leek, shallot, chive
• Carrot Family: Carrot, parsnip, parsley, celery
• Cabbage Family: Cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, turnip, radish, Chinese cabbage, kale, collards, rhutabaga
• Beet Family: Beet, Swiss chard, spinach
• Pea Family: Peas, snap bean, lima bean, soybean
• Okra Family: Okra
• Corn Family: Sweet corn, field corn, wheat, barley, oats

Some choices of crop rotations include Pea Family to Corn Family, Lettuce Family to Cucumber Family, Cucumber Family to Cabbage Family, and Cucumber Family to Corn Family. Rotating beans with a grain crop such as barley, oats, rye, wheat, or field corn or with a forage crop is very beneficial for root-rot control. One or two years in a grain crop is often long enough to prevent severe root rot when the field is not heavily infested with this disease.

Some diseases that come from the soil are not easily controlled by rotation. Such diseases can live a long time in the soil and are not affected by rotation. Examples include clubroot that attacks the Cucumber Family, Phytophthora blight, and Fusarium wilt of several crops. Other diseases attack so many vegetables that they can survive indefinitely on many different plants including weeds. These diseases include Sclerotinia, Rhizoctonia, Verticillium and root-knot nematodes. 

Many diseases can survive successfully because they can live on plants and plant parts left in the field after harvest. However they are unable to survive once the plants left in the field decompose. Destruction of plants and parts of plants left in the field after harvest can eliminate this problem. Plowing the field after harvest and before letting the soil rest can reduce the amount of disease that will survive.