V, F, and N

The letters V, F, and N on a seed packet or plant label refer to certain types of disease resistance and pest tolerance.

All of us work to make our plants healthier. At the end of a growing season, many of us save seeds from the very best fruits and plants for next year. [If you’ve never done this before, I urge you to give it a try. I’ll write about seed saving tomorrow.] By saving and planting seeds from the best plants each year, we are choosing specimens that are better suited to our microclimate and personal tastes.

Building better plants

When we save and plant seeds from specific plants, we are cultivating certain characteristics. A more intensive method of building better plants is to purposefully pollinate one plant with the pollen of another. Taken to the far end of this spectrum, we have plants that are genetically modified in the lab. [I used to be bothered by this, until I learned that plants have been doing it to each other for a very long time. See Dodder.] These manipulations are often used to encourage certain characteristics such as color, flavor, days to maturity, disease resistance, or pest tolerance.

Disease resistance and pest tolerance

Some plants are susceptible to certain diseases, while others are not. The same is true for pest infestations. In both cases, you can generally use the disease triangle to reduce the impact pests and diseases have on your garden. The disease triangle consists of the environment, the plant, and the problem. Change one of those three and the problem can be reduced or eliminated. Installing plants that are already resistant to some of your garden’s more common problems can reduce your workload and keep your plants healthier. That’s where V, F, and N come in.

V is for verticillium wilt

The V tells you that a particular plant is resistant to verticillium wilt. Verticillium wilt is a soil-borne fungus that attacks tomatoes, peppers, berries, snapdragon, eggplant, potatoes, and over 300 other garden edibles. Plants infected with verticillium wilt exhibit chlorosis, wilting, and leaf drop as the fungi breed, blocking the flow of water and nutrients through vascular tissue. Verticillium wilt fungi can stay in the soil for several years, so infected plants should be thrown in the trash. If you have a garden patch affected by verticillium wilt, use crop rotation and plant non-host species, such as beans and other legumes, broccoli, corn, and cereal grains. Non-host species are not affected by this disease.

Dahlia plants infected with Verticillium wilt (Howard F. Schwartz) CC BY 3.0

F is for fusarium wilt

Fusarium wilt is another soil-borne fungal disease. As these fungi (Fusarium oxysporum) reproduce, they cause bleaching, chlorosis, stunting, damping off, and brown veins. Fusarium wilt  frequently attacks peas, beans, and other legumes, tomatoes, tobacco, sweet potatoes, cucumber and other cucurbits and even banana plants. There are actually several different strains of Fusarium wilt, so you may see F, FF, or FFF, depending on which strain the plant is resistant towards. [Check with your local County Extension Office to learn which strain is in your area.]

Peas infected with Fusarium wilt

N is for nematodes

There are good nematodes and there are bad nematodes. Bad nematodes feed on the roots of several different garden plants and fruit trees. Aboveground symptoms include afternoon wilting, chlorosis, and a general lack of vigor. To verify a nematode problem, you have to dig the plant up. Nematode feeding causes swollen areas, called galls, on the roots. Roots will also look stunted and deformed.

Nematodes burrow into root crops (William Wergin, et al) CC BY 2.0

Seeing V, F, and N is not a guarantee. It simply tells you that a particular variety of plant is resistant. Sometimes, that little extra resistance can make all the difference.