Your Plants May Have That Run-Down Feeling

With the winter flu season upon us, what better time to consider plant viruses? Plants don’t get fevers, runny noses, or achy joints, but have other ways of expressing their distress when infected by viruses.

Symptoms depend on the type of virus and the type of plant. You may have seen pale yellow mottling or crinkling of the leaves, or growth may have become inexplicably stunted. Any of these symptoms could have been caused by a viral infection. Symptoms might even come and go, showing up, for example, when cool temperatures slow growth.

A big difference in the way plants and animals react to viruses is that animals can fight off their infections, but plants cannot.

No medicines (sprays) can help, either. Only in certain cases has human intervention helped, and that is when a plant, but not its virus, could tolerate a heat treatment lasting from a few hours to a few weeks. Sort of like curing a plant by giving it an artificial fever. Instead of curing a plant, propagating new ones from cells in stem tips can give rise to virus-free offspring.

Lacking wings or legs with which to fly or crawl or a mouth with which to chew itself into a plant, viruses need help. They are adept hitchhikers, traveling in the gut of certain insects, nematodes, even fungi, then silently slipping into a plant cell as any of these organisms begin feeding on a plant.

So one way to prevent virus infections in plants is to control insects or other organisms that spread viruses. Another control is to isolate cultivated plants from related wild plants and weeds, both of which might harbor viruses.

Aphids, for example, can carry cucumber mosaic virus from ragweed or milkweed to cucumbers, or raspberry mosaic virus from wild raspberries to cultivated raspberries. Rip out any cultivated plant known to be infected with a virus.

Plant viruses even get rides from humans. Tobacco mosaic virus infects a wide variety of plants and can be carried on smokers’ fingers.

Plant choice can help avoid virus problems. Some varieties are virus-resistant. Others are “certified virus-free,” meaning they’re initially free of infection and it’s up to you to keep them so.

Don’t blame all your plant problems on viruses. Definitive diagnosis is often difficult without a laboratory test. Perhaps you’re just overwatering.