Many companies offer seeds and propagative parts that are certified virus-free. It is important to inspect new transplants or seedlings for signs of viral infection. Infected plants often stand out from healthy plants because they are stunted, yellowed, or show a mosaic pattern on the leaves. But some of these symptoms may reflect problems unrelated to viruses. Any suspicious plants should be removed to avoid infection of nearby plants.
Weeds can carry many common viruses, which is another good reason to weed regularly or to mulch.
As tempting as it may be to try to protect your plants by killing potential insect vectors with insecticides, this usually isn't effective in preventing virus transmission. A single insect can inoculate a plant in just seconds. Viral diseases can be a serious problem for home gardeners. But many seed catalogs offer cultivars with genetic resistance to the more troublesome viruses, so look for them if you have had problems. Buying virus-free seeds and propagative parts, weeding, and removing suspicious plants early in the year are usually sufficient to keep viral disease at bay.