Soil, Crop and Pest Management

Virus Diseases of Vegetable Crops

Virus Diseases of Beans

Bean Common Mosaic Virus (BCMV) In addition to mosaic and lesions of the foliage, BCMV can also cause blackened roots. Several different strains of the virus are recognized and the symptoms and host range varies according to the strain. The virus can be seed-borne and is transmitted by at least 12 species of aphids in a nonpersistent manner. Resistant cultivars are available and constitute the most reliable means of control. Seed treatment, insecticides and roguing of diseased plants are of little value.

Bean Yellow Mosaic Virus (BYMV) Many strains of this virus are known. Symptoms of BYMV are easily confused with BCMV. However, BYMV is not seed-borne and unlike BCMV, BYMV is spread in a persistent manner by more than 20 species of aphids. Entire plantings may become infected resulting in substantial losses in yield. Disease outbreaks are often correlated with the presence of virus-source plants such as sweet clover, white clover, crimson clover and Gladiolus sp. Since the virus overwinters in legumes such as clover and vetch, beans should be planted at least 800 feet away. Insecticides applied early will reduce spread. Few resistant cultivars are available.

Virus Diseases of Cucurbits

Cucumber Mosaic Virus (CMV) Many different strains of this virus occur and the host range includes plants in more than 31 different families. Many weed species serve as hosts. The virus is spread by more than 40 species of aphids and 2 beetles in a nonpersistent manner. Seed transmission is also possible but probably infrequent in commercial seed. The abundance of reservoir plants and their proximity to crops and the presence of vectors govern the severity of epidemics. The use of resistant cultivars is the most effective means of control. Reduce weeds as much as possible. Practice rotation and plant away from previously contaminated fields. Insecticides are not very effective.

Watermelon Mosaic Virus (WMV) and Papaya Ringspot Virus (PRSV-W) Two related viruses, previously designated Watermelon Mosaic I and II have been verified in the northeast; WMV-II appears to be more prevalent. Watermelon Mosaic Virus-I is now known to be Papaya Ringspot Virus. Regardless of strain, symptoms may be mild or severe and significant reduction in yield may occur. Several aphid species transmit the virus in a nonpersistent manner. PRSV-W is only known to occur in the cucurbit family but WMV-II has been reported from alfalfa, vetch, crimson clover, sour clover, snow-on-the-mountain, and Malva parviflora. Seed transmission is considered a possibility but remains unproven. At this time, resistant cultivars cannot be recommended.

Zucchini Yellow Mosaic Virus (ZYMV) Zucchini Yellow Mosaic Virus was first discovered in the United States in the early 1980's. It is likely to have occurred before that time but confused with other cucurbit viruses. Two strains are currently recognized: "Connecticut" and "Florida". The Connecticut strain produces more severe symptoms than the Florida strain. The virus is transmitted in a nonpersistent manner by aphids. At this time, no weed hosts have been identified. Circumstantial evidence exists that the virus can be seed-borne. At this time resistant cultivars are not available.

Virus Diseases of Peppers

Cucumber Mosaic Virus (CMV) Many different strains of this virus occur and the host range includes plants in more than 31 different families. In pepper, the symptoms can be confused with Tomato Spotted Wilt Virus (TSWV) as well as other virus diseases. The disease is spread by several species of aphids in a nonpersistent manner. Reduce weeds, especially pokeweed and milkweed as much as practical. Isolate pepper fields from cucurbits especially where there has been a history of CMV. Resistant cultivars cannot be recommended at this time.

Tobacco and Tomato Mosaic Virus (TMV, TomMV) Several strains of TMV exist including the closely related tomato (TomMV) strain. Symptoms on pepper and tomato can vary considerably as will the severity of disease and the effect on yield. Either strain can be seed-borne or transferred from previously infected plant debris, weeds, transplants, other crops, or workers using tobacco products. Unlike other viruses, TMV and TomMV are easily spread from plant to plant by contact with hands and tools. Insects are not considered to be important vectors. Grow resistant cultivars. Control weeds as much as practical. Do not plant peppers or tomatoes for at least two years on land that previously had TMV-infected crops. Handle plants as little as possible. Do not allow workers to use tobacco products while working with plants.

Tomato Spotted Wilt Virus (TSWV) Tomato Spotted Wilt Virus has caused considerable losses in vegetable crops such as tomato, pepper, celery and lettuce in the southern and western United States for many years. Only recently has it begun to be a problem in the eastern and northeastern United States. The recent occurrence of TSWV in our region is attributed to the introduction of the insect vector (mostly the western flower thrips) and the movement of infected plant material. The host range for TSWV is one of the largest of any virus. More than 170 plant species are susceptible including many commercial floriculture crops. At this time TSWV is more of a problem on greenhouse crops (ornamentals) than vegetable crops. The name of the virus is derived from the symptoms that develop on tomato. On pepper, the symptoms are easily confused with CMV and TMV. On other hosts, the symptoms are considerably variable. Two strains are currently recognized: "lettuce" and "impatiens". Both strains have been found in vegetables and ornamentals. However, recent studies indicate that the impatiens strain is a closely related but apparently different virus. Do not raise tomato, pepper, eggplant or cauliflower transplants in the same greenhouse as ornamentals. Monitor thrips and control as necessary. Resistant cultivars are not available at this time.

Virus Diseases of Potato

Potato Leafroll Virus (PLRV) Potato Leafroll Virus is the most serious virus disease of potatoes in New England and can result in significant yield reductions. The virus is transmitted by aphids in a persistent manner. The virus can overwinter in unharvested tubers which may develop into virus-infected volunteer plants. Plant virus-free certified seed. Remove volunteer plants. Rogue plants with virus symptoms. Insecticides do not adequately control PLRV.

Potato Virus S (PVS), Potato Virus A (PVA) and Potato Virus X (PVX) These viruses may occur singly or in combination with each other. PVS and PVA are spread by aphids in a nonpersistent manner. PVX is not known to be spread by insects but is easily spread by plant-to-plant contact, farm machinery or cultural practices. Plant virus-free certified seed.

Virus Diseases of Corn

Maize Dwarf Mosaic Virus (MDMV) Several strains of MDMV are known and they are spread by more than 20 species of aphids in a nonpersistent manner. The virus can be seed-borne in maize and probably in some annual grasses. The virus is nonpersistent but is retained by the aphid for up to 18 hours. This would allow time for the vector to be transported from southern states where MDMV is more prevalent and many perennial and annual weed hosts occur. Johnsongrass is an important perennial weed host for MDMV and occurs in southern New England. Plant resistant or tolerant varieties. Golden Gleam, Sundance, Spring Gold, Seneca Star, Early Fortune, Sugar Loaf, Dandy and Capitan have some tolerance. Enforcer, Biguard, Silver Red, and Seneca 258 are resistant. Eradicate johnsongrass.

Virus Diseases of Tomato

Cucumber Mosaic Virus (CMV) Many different strains of this virus occur and the host range includes plants in more than 31 different families. In tomato, the symptoms can be confused with Tobacco Mosaic as well as other virus diseases. The disease is spread by several species of aphids in a nonpersistent manner. Reduce weeds, especially pokeweed and milkweed as much as practical. Isolate tomato fields from cucurbits especially where there has been a history of CMV. Resistant cultivars cannot be recommended at this time.

Tobacco and Tomato Mosaic Virus (TMV, TomMV) Several strains of TMV exist including the closely related tomato (TomMV) strain. Symptoms on tomato can vary considerably as will the severity of disease and the effect on yield. Either strain can be seed-borne or transferred from previously infected plant debris, weeds, transplants, other crops, or workers using tobacco products. Unlike other viruses, TMV and TomMV are easily spread from plant to plant by contact with hands and tools. Insects are not considered to be important vectors. Grow resistant cultivars. Control weeds as much as practical. Do not plant peppers or tomatoes for at least two years on land that previously had TMV-infected crops. Handle plants as little as possible. Do not allow workers to use tobacco products while working with plants.

Tomato Spotted Wilt Virus (TSWV) Tomato Spotted Wilt Virus has caused considerable losses in vegetable crops such as tomato, pepper, celery and lettuce in the southern and western United States for many years. Only recently has it begun to be a problem in the eastern and northeastern United States. The recent occurrence of TSWV in our region is attributed to the introduction of the insect vector (mostly the western flower thrips) and the movement of infected plant material. The host range for TSWV is one of the largest of any virus. More than 170 plant species are susceptible including many commercial floriculture crops. At this time TSWV is more of a problem on greenhouse crops (ornamentals) than vegetable crops. The name of the virus is derived from the symptoms that develop on tomato. On other hosts, the symptoms are considerably variable. Two strains are currently recognized: "lettuce" and "impatiens". Both strains have been found in vegetables and ornamentals. However, recent studies indicate that the impatiens strain is a closely related but apparently different virus. Do not raise tomato, pepper, eggplant or cauliflower transplants in the same greenhouse as ornamentals. Monitor thrips and control as necessary. Resistant cultivars are not available at this time.

note: this information was prepared for the 1990 New England Vegetable Production Recommendations. Please forward any comments or suggestions for revision to R. L. Wick