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. Consult catalogs and local nurseries for other disease-resistant varieties as well, as new ones come out each year and some of the old ones get discontinued. For more information about disease resistance call your local Master Gardener Program at your county office of the OSU Extension Service.