By Zhihan Xu
Iowa State University
Hosta breeders and hobbyists are always looking for unique leaf colors and patterns, in hopes of discovering new, attractive and profitable varieties. In a cruel twist of fate, you may discover a new look on your hostas that is caused by a virus disease rather than a natural variation.
The culprit is a fairly new but fast-spreading disease called hosta virus X (HVX). Since the symptoms of the virus sometimes look so similar to the normal variegation in leaf color of certain healthy hostas, the diseased hostas can be inadvertently sold and spread through the marketplace.
For example, before much was known about viruses in hostas, some infected plants were named as new varieties. It turned out that the varieties ‘Breakdance,’ ‘Eternal Father’ and ‘Leopard Frog’ looked different from their parents only because they were sick with a permanent virus infection. Once these disease carriers were introduced, the virus was transmitted to healthy hostas. Needless to say, these varieties were withdrawn from the market.
The most common symptoms of hosta virus X are mottlingand irregular green or blue color on leaves. The mottling appears to “bleed out” from the main leaf veins into surrounding tissue. After long-term infection, leaves can be stunted, twisted or puckered.
It is true that some hosta varieties have mottling patterns similar to those created by hosta virus X. However, healthy plants usually don’t have mottling patterns that follow the leaf veins – the telltale signs of the virus. Instead, the mottling patterns of healthy plants are spread out evenly over the leaf surface. Healthy plants also lack sunken and wrinkled leaves.
Hosta virus X has infected thousands of plants and has been spread around the world. In 1996, it was the most common virus in a survey of Midwestern states. The Iowa State University Plant Disease Clinic started receiving more and more hostas infected with hosta virus X in the last few years. Although most of the virus-positive hosta samples were from commercial nurseries, hosta virus X may become more common in home gardens.
The original source of host virus X is unknown, but large numbers of infected plants were apparently shipped inadvertently by wholesale growers in The Netherlands. Infected plants soon began to appear in several nurseries and big-box stores in the United States.
Hosta virus X can be spread by transferring sap from the infected plants to healthy plants. Disease can be easily spread when dividing crowns or trimming old leaves and flowers. If any hosta plants in a shipment show HVX symptoms, the whole batch should be considered infectedand then discarded, because the disease is so easily transmitted.
The best way to avoid HVX is to keep infected plants out of your garden. Carefully inspect hostas for any evidence of virus symptoms before you buy them. Of course, it helps to buy plants from reputable sources.
Virus-infected plants cannot be cured, so they should be dug up and destroyed. Merely cutting off the sick-looking leaves won’t save the rest of the plant, since the virus invades all plant parts.
Several hosta varieties have been reported to be resistant or immune to HVX. These include ‘Blue Angel,’ ‘Color Glory,’ ‘Frances Williams,’ ‘Bressingham Blue,’ ‘Frosted Jade’ and ‘Love Pat.’ Susceptible varieties include ‘El Capitan,’ ‘Francee,’ ‘Halcyon’ and ‘Cherry berry.’
Hosta is the only known host plant for HVX, so other types of plants in your home garden are free of the disease. On the other hand, several other viruses with wider host ranges can infect hosta.
Impatiens necrotic spot virus appears most commonly on hosta in the southeast and is transmitted by thrips. Both tomato ringspot virus and tobacco rattle virus can be transmitted by tiny, root-feeding, worm-like creatures called nematodes. They produce mottling, yellowing, browning and areas with concentric yellowish rings.
Applications of labeled insecticides or nematicides may reduce the risk of some of these viruses. But HVX is an exception, since it is transmitted primarily by handling and wounding rather than by pests.
If you are wondering whether that funny-looking hosta in your garden is infected with a virus, the best way to be sure is to have it tested. The ISU Plant Disease Clinic is a good place to send plant samples for virus testing. Samples can be sent to the Clinic from ISU Extension county offices, or directly to the Clinic at 351 Bessey Hall, ISU, Ames 50011. The phone number of the Clinic is (515) 294-0580. A $10 fee per sample is charged for diagnosis.