Avoid over-watering and wounding of plants. Plants may be dwarfed with small leaves showing mottling or chlorosis. Flowers are characteristically green or flower parts may be leaf-like. A bunchy flowerhead is typical. This pathogen is spread by leafhoppers and has many plant hosts, including aster, ragweed, and chrysanthemums.
Control consists of removing all infected or suspicious plants and control of leafhopper vectors.
A number of different viruses can attack perennials. These viruses are obligate parasites which are not themselves alive, but use plant cell metabolism to replicate and produce more virus. Viruses can be transmitted by mechanical means such as touching or rubbing leaves with hands or tools contaminated by contact with diseased plants, by dodder, nematodes, grafting or insects such as aphids, leafhoppers, whiteflies, or thrips. Control is based on starting with virus-free stock or seeds, control of insect vectors, eliminating weed virus hosts, resistant varieties, and eliminating diseased plants. The northern root-knot nematode, M. hapla , is a sedentary endoparasite, meaning that it infects host roots after hatching from eggs, stimulating the formation of a small gall containing specialized feeding cells, and feeds in the same location through several molts to produce several hundred offspring.