Plant viruses

About

Viruses are tiny germs that live inside a plant's cells. None can be cured, so the goal is to spot them early, pull sick plants, and keep the insects and weeds that carry them in check. This page covers what they have in common; the guide has its own page for each of the common garden viruses, from cucumber mosaic and tomato spotted wilt to curly top, potato virus Y and the orchid viruses.

Also called viruses, virus, plant virus, viral disease, viral diseases, virus disease, virus diseases

How to recognize it

Symptoms

Leaves mottled in light and dark green or yellow (a mosaic), yellow rings, lines or vein patterns, and leaves that pucker, cup, curl or grow narrow and stringy. Plants are often stunted, and fruit can be small, warty, blotchy or misshapen. Signs are usually clearest on the newest growth.

Often confused with

Herbicide drift, nutrient shortages, cold or heat stress, and mite or thrips feeding can all look like a virus. Only a lab test identifies a virus for certain; your county Extension office can help.

Worse when

Busy aphid, thrips or whitefly populations, weeds and perennial plants nearby that carry viruses, seed or cuttings saved from sick plants, and handling tobacco before touching tomatoes or peppers.

How it spreads

Mostly by insects that feed on a sick plant and then a healthy one. Some move on seed, cuttings, bulbs and divisions, and tobacco and tomato mosaic also spread on hands, tools and clothing. Many wait out the winter in weeds and perennials.

When

Spring through fall, whenever the insects that carry them are active.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Resistant varieties and clean seed Prevent

   Choose varieties listed as resistant (seed catalogs use codes such as CMV, TSWV or TYLCV), and buy clean seed, transplants, bulbs and cuttings. Don't save seed or take cuttings from plants that looked sick.

   Resistance is not immunity, so keep up the other steps too.

2. Keep weeds down Prevent

   Many viruses spend the winter in weeds and perennial plants. Keep weeds out of and around the garden, and don't plant cucumbers, squash, peppers or beans right next to alfalfa or clover.

3. Pull sick plants and wash up By hand

   There's no cure. Pull and bag plants with clear virus signs as soon as you see them, so insects can't carry it to the rest. Wash your hands and tools afterward, and don't use tobacco while handling tomatoes and peppers.

4. Row covers and reflective mulch Barrier

   Floating row cover keeps aphids, whiteflies and thrips off young plants; lift it when crops that need bees start to flower. Silver reflective mulch helps keep aphids and thrips from landing.

5. Insect sprays rarely stop viruses Organic spray

   Aphids pass many viruses in seconds, before any spray can work, so insecticides do little to stop the spread. Where whiteflies or thrips are heavy, soap, oil or neem can lower their numbers.

   Follow the label, and spray in the evening when bees aren't flying.