Roses, fruit trees and many vegetables such as tomatoes are susceptible to variety of diseases caused by fungi and viruses. Try and choose those marked 'disease resistant' or 'certified virus-free' whenever possible. For example, tomato seed packages and start tags often are marked with the letters V, N, T, or F. V signifies resistance to verticillium, a fungal disease causing premature wilt and reduced production. N stands for a nematode-resistant variety. Nematodes are small wormlike pests that puncture root cells.
T indicates resistance to tobacco mosaic virus, which causes mottled leaves.
An F means the variety is resistant to fusarium, a fungal disease that also causes wilt. Other vegetables have disease resistant or disease tolerant varieties as well, including green beans, peas, cucumbers, peppers and spinach. The fungal diseases rust, powdery mildew and blackspot are common in rose gardens in the Pacific Northwest. Apples are susceptible to a number of diseases including apple scab, fire blight and powdery mildew. Crab apples have the same problems, so Pscheidt recommends planting disease-resistant crab apple cultivars David, Indian Summer, Red Jewel or White Angel.