How to Manage Pests

UC Pest Management Guidelines

COMMENTS ON THE DISEASE
Viruses multiply only in living cells of plants and animals. They are too small to be seen with a light microscope. They are composed of nucleic acid and proteins. The nucleic acid of most plant viruses is ribonucleic acid (RNA); a few plant viruses (carnation etched ring virus, dahlia mosaic virus) are composed of deoxyribonucleic acid (DNA). Viroids consist of low molecular weight RNA but no protein coat. Chrysanthemum stunt and chrysanthemum chlorotic mottle are examples of viroid diseases.

Positive identification of virus infection involves visualization with the electron microscope, serological techniques such as ELISA (enzyme linked immunosorbance assay), sap inoculations of indicator plants, budding and grafting to indicator plants, microscopic examination for inclusion bodies (aggregates of virus particles), RNA and DNA hybridization, and gel electrophoresis.

Insects, especially aphids and leafhoppers, vector (transmit) many viruses, and thrips vector tomato spotted wilt virus. Mites, nematodes, and lower fungi also serve as vectors of a few viruses.

A few plant viruses and viroids are spread by contact handling or by tools. Some orchid viruses are spread when healthy plants come in contact with diseased ones. Some viruses are pollenborne (cherry leaf roll virus, prunus necrotic ringspot virus). A few viruses are seedborne (squash virus in muskmelons, tobacco ringspot virus in soybean, and others). Many are transmitted by vegetative propagation of plant material from infected plants.

MANAGEMENT
Control of virus diseases is a matter of prevention and the use of virus-free planting stock. Once a plant is infected by a virus it usually remains infected for the life of the plant. Plants vegetatively propagated from such material are usually infected. However, virus-free plants can be obtained from infected plants by a combination of heat treatment and shoot tip culture, and sometimes with the aid of chemical inhibitors of virus multiplication. To prevent spread of the virus, control insect vectors and weeds that may harbor the virus. Sometimes nematode control may reduce spread as well.

VIRUSES WITH WIDE HOST RANGES

Virus	Transmission	Ornamental hosts	Crop plant hosts	Weed and native plant hosts
Bean yellow mosaic (potyvirus group)	aphids; mechanically to an extent in gladiolus	gladiolus, sweet pea, violets	legumes, bean, clovers, fava bean, pea, soybean, sweet clover	legumes, Chenopodium, clovers, sweet clover
Beet curly top (rhabdovirus group)	leafhoppers	cosmos, coreopsis, geranium, nasturtium, petunia, strawflower, stock, viola, zinnia	bean, beets, borago, buckwheat, celery, clovers, cress, cucurbits, fava bean, fennel, flax, horseradish, pepper, potato, radish, rhubarb, tobacco, tomato, vetch	Atriplex spp., Chenopodium spp., clovers, fennel, Polygonium spp., Rumex spp., Russian thistle, shepherd's-purse
Cauliflower mosaic (caulimovirus group)	aphids	honesty (lunaria), stock	crucifers, broccoli, cabbage, cauliflower, chinese cabbage, mustard	mustard, Raphanus spp., shepherd's-purse
Cucumber mosaic (cucumovirus group)	aphids; mechanically in a few hosts	begonia, buddleia, calendula, china aster, columbine, dahlia, daphne, delphinium, geranium, gerbera, gladiolus, ligustrum, lily, lobelia, nasturtium, primula, snapdragon, vinca, viola, zinnia	buckwheat, carrot, celery, cucurbits, cowpea, passionvine, pepper, potato, spinach, tobacco, tomato	commelina, lambsquarter, lupine, milkweed, nightshade, penstemon, pigweed, pokeweed
Prunus necrotic ringspot (ilarvirus group)	grafting; pollen	Prunus spp., rose	apple, hops, Prunus spp.	Prunus spp.
Tobacco mosaic (tobamovirus group)	mechanical; seeds may be externally contaminated, can be soilborne	delphinium, petunia, phlox, wisteria, flowering tobacco	beans, tobacco, tomato	emilia
Impatiens necrotic spot virus and/or tomato spotted wilt (tomato spotted wilt group)	thrips	amaryllis, aster, ageratum, begonia, calendula, calla, chrysanthemum, coreopsis, cosmos, dahlia, forget-me-not, gerbera, gladiolus, gloxinia, gypsophila, impatiens, kalanchoe, lily, nasturtium, papaver, petunia, phlox, primula, ranunculus, salvia, stock, sweet pea, tagetes, verbena, zinnia, and others	artichoke, bean, cauliflower, celery, clover, cowpea, endive, fava bean, lettuce, papaya, pea, peanut, pepper, pineapple, spinach, tobacco, tomato, and others	bindweed, chickweed, emilia, jimsonweed, knotweed, lupine, malva, Mesembryanthemum, miner's lettuce, physalis, pigweed, nightshade, shepherd's-purse, and others
Turnip mosaic (potyvirus group)	aphids	anemone, nasturtium, petunia, statice, stock, sweet william, wallflower, zinnia	brussels sprouts, cabbage, cauliflower, cress, horseradish, mustard, radish, rape, rhubarb, swede turnip	cruciferous weeds

PUBLICATION

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
R. D. Raabe (emeritus), Environmental Science, Policy, and Management (ESPM), UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego Co.
A. H. McCain (emeritus), Environmental Science, Policy, and Management (ESPM), UC Berkeley

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