Vegetable Production Update – July 6, 2018

— Written By

From Dr. Amanda Strayer-Scherer (Postdoctoral Research Scholar, Plant Pathology, Tomatoes) and Inga Meadows (Extension Associate, Plant Pathology Specialist)

Background: The information presented in this vegetable production update contains a summary of the details discussed in the one-hour, biweekly vegetable production conference calls entitled Veggie Calls. These open forum sessions were developed to allow extension personnel (agents, area specialized agents [ASAs], and specialists) to discuss challenging cases, seek advice on recommendations, report emerging issues, and share training opportunities related to vegetable production. These calls are hosted by Inga Meadows, Dr. Amanda Strayer-Scherer, and/or Dr. Lina Quesada-Ocampo every two weeks throughout the vegetable production season.

Attendees (description) of the July 6 Veggie Call: Mary Jac Brennan (Extension Agent, Forsyth County), Johnny Coley (Extension Agent, Granville County), Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology), Daniel Overcash (NCDA Agronomist), and Amanda Scherer (Postdoctoral Research Scholar, Plant Pathology).

Vegetable Production Updates:

  1. Two reports of cucumber beetles and bacterial wilt on high tunnel cucurbits and field cucumbers in two counties in western North Carolina.
  2. Early blight has been reported on tomatoes in two counties in north-central and western North Carolina.
  3. Bacterial wilt was reported on tomatoes in western North Carolina.
  4. Tomato spotted wilt virus was reported on field and greenhouse tomatoes in two counties in western North Carolina. In the greenhouse, the disease can affect up to 100% of the tomatoes. In these cases, producers are advised not to plant them in the field as the transplants will not recover.
  5. Baby sweet bell peppers in north-central North Carolina have dark areas on the stem at the crown. However, the roots and vascular tissue appear to not have any issues. Approximately 15% of the 9-acre field are affected and it is worse in lower parts of the field. The symptoms were likely caused by a Phytophthora species.
  6. Collar rot (Alternaria linariae, the same pathogen that causes early blight) has been reported on field tomatoes in western North Carolina. Inoculum comes from the greenhouse, and the pathogen will cause the stem to girdle and can kill the plant. If it is caught early, then you can build up soil around the stem lesions and the plants can recover.
  7. Cucurbit Downy Mildew has been reported in Duplin, Edgecombe, Johnston, Nash, Salem, Sampson, Wake, and Wilson Counties. For updates on the 2018 epidemic history of cucurbit downy mildew, please visitthe Cucurbit Downy Mildew Epidemic History for 2018 page for more information.
  8. Southern blight has been reported on field tomatoes in western North Carolina. Sclerotia and white hyphae could be seen on the stem near the soil line. The soil was not fumigated, and disease incidence was spotty throughout the field.
  9. Phytophthora Crown and root rot has been reported on zucchini in western North Carolina.
  10. Bacterial spot was reported on field tomatoes in western North Carolina.
  11. High tunnel tomatoes in western North Carolina displayed dark-brown lesions may be encircled by concentric rings. Although early blight was suspected, it was identified as Septoria leaf spot.
  12. Blossom end rot has been reported on tomatoes in western North Carolina. Blossom end rot is typically due to calcium deficiency in the distal end of the fruit. Rapidly growing plants 1 to 3 weeks past the flowering period of the plant are most susceptible. Fruit will initially have light-tan, water-soaked lesions on at the blossom end of the fruit which will enlarge and turn black and leathery. They can often become overrun with secondary black mold. Soil testing is recommended to determine if there is a shortage in calcium.
  13. There were two reports of tomato plants with necrotic spots and tip burn in western North Carolina. The first was reported in field tomatoes in raised beds and the second was in home garden tomatoes. In the field-grown tomatoes, the pattern did not look like disease and tests revealed that the soil was high in phosphorus and potassium (P+K). Soil pH was also at 7.3.
  14. Several reports of green beans with white interveinal discoloration on the bottom of leaves in western North Carolina. It does not appear to be detrimental to yield. It appears to be some sort of abiotic disorder, perhaps ozone damage.
  15. Home garden watermelons have bleached out spots on leaves or the entire leaf is bleached out in north-central North Carolina. There were no signs of fungal growth and is suspected to be ozone damage.

Upcoming Events:

  1. Mountain Research Station Field Day on Thursday July 19, 2018 at 2:00 pm (research updates, trade show, entertainment, and more!) (Waynesville, NC).
  2. 3-In-1 Alternative Crops and Organics Day on Wednesday July 25, 2018 from 8:30 am to 6:00 pm at the Mountain Research Station (Waynesville, NC). More information and registration.
  3. Mountain Horticultural Crops Research and Extension Center 2018 Tomato Field Day August 16 (field tours, lunch, research initiatives, taste tests, and more!) (Mills River, NC).

Pest News and other Announcements:

  1. Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology): Explained to the group that we plan to publish summaries of the Veggie Calls with important pest information in the NCSU Extension Pest News and will keep track of the names of the attendees to give them credit in the published summaries. These published summaries will be accessible to vegetable producers, ASAs, county extension agents, extension specialists, and researchers with an interest in North Carolina’s vegetable production industry.
  2. Amanda Scherer (Postdoctoral Research Scholar, Plant Pathology): Amanda is a new postdoctoral research scholar with Inga Meadows at the Mountain Research Station in Waynesville, NC. Part of her research is to look at the pesticide sensitivities of the bacterial spot and early blight of tomato pathogens.
    1. For bacterial spot, they are focusing on tomato transplant producers and are asking for help from extension agent in collecting greenhouse tomato samples with bacterial spot symptoms.
    2. For early blight, they are focusing efforts on collecting tomato samples with early blight symptoms from commercial fields in North Carolina.
    3. These samples will help provide us with valuable information on how to better advise growers in North Carolina to manage these two diseases. If you are interested or available to help them with this project, then they can send shipping labels and simple instructions for collecting samples. Please contact Amanda (alstraye@ncsu.edu) or Inga (inga_meadows@ncsu.edu) for more information.

Additional Information on the Vegetable Plant Pathogens Mentioned in this Vegetable Production Update: 

Bacterial Spot is caused by four species of Xanthomonas (X. euvesicatoria, X. gardneri, X. perforans, and X. vesicatoria) and occurs worldwide wherever tomatoes are grown. In North Carolina, X. perforans is predominant species associated with bacterial spot on tomato. Due to diversity within the bacterial spot pathogens, the disease can occur at different temperatures and is a threat to tomato production worldwide. Disease development is favored by temperatures of 24 to 30℃ (75 to 86 ℉) and high precipitation. Bacterial spot can cause leaf and fruit spots, which causes defoliation, sun-scalded fruit, and yield loss.

  • Symptoms: In general, spots are dark brown to black and circular on leaves and stems. However, leaf lesions are initially circular and water-soaked and young lesions may be surrounded by a faint yellow halo. Spots rarely develop to more than 3 mm in diameter. Lesions can coalesce causing a blighted appearance of leaves and a general yellowing may occur on leaves with multiple lesions. Fruit lesions begin as small, slightly raised blisters, which become dark brown, scab-like, and slightly raised lesions as thy increase in size.
  • Signs: On leaflets, bacterial spot can be easily confused with the early symptoms of bacterial speck, early blight, gray leaf spot, target spot, or Septoria leaf spot. When Xanthomonas is present, bacteria will ooze (also referred to as bacterial streaming) from infected tissue and can be observed under a light microscope. Bacterial streaming will not be observed in lesions caused by fungal pathogens.
  • Management: Management of the disease focuses on preventive control measures throughout the season. The most effective management strategy is the use of pathogen-free certified seed and disease-free transplants. Seeds may be treated with sodium hypochlorite, hydrochloric acid, or hot water to reduce the potential for seedling infection. In transplant production greenhouses, minimize overwatering and handling of seedlings. Trays, benches, tools, and greenhouse structures should be washed and sanitized between seedlings crops. Greenhouse tomatoes can be sprayed with bacteriophages, copper-based bactericides, or streptomycin. Streptomycin CANNOT be sprayed in field tomatoes. For field tomatoes, copper in combination with mancozeb and plant activators, such as acibenzolar-S-methyl, can be used.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 39-40). St. Paul, MN: APS press.
    2. Meadows, I., and Henson, M. 2017. Bacterial Spot of Pepper and Tomato. North Carolina State University. Plant Disease Fact Sheet. Retrieved May 16, 2018.

Bacterial Wilt of cucurbits is caused by the bacterial pathogen Erwinia tracheiphila and is a serious threat to commercial muskmelon and cucumber production in the midwestern and eastern United States. It only affects certain members of the cucumber family including cucumber, squash, muskmelon, pumpkin, and gourd. The disease is less damaging to squash, pumpkin, and watermelon. Bacterial wilt can cause losses of 10 to 20 percent in unsprayed plantings of susceptible cucurbits. The disease is spread within and between filed by stripped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctat howardi, respectively). Environmental conditions that favor the over-wintering, feeding, and reproduction of cucumber beetles will affect disease incidence.

  • Symptoms: Symptoms can vary among crop species. However, the disease will first appear on single leaf which will wilt suddenly and be dull green in color. The wilting symptoms will then spread up and down the runner. In cucumber and melon, individual vines or whole plants will wilt and die rapidly. Affected vines will be dark green initially and then will be become necrotic as the disease progresses. In summer squash and pumpkin, plants may wilt dramatically in the heat of the day but may partially recover by the next morning. A distinct chlorosis and necrosis will develop around leaf margins before the entire plant collapses and dies. Less susceptible plants, such as certain squash varieties, may be stunted/dwarfed before wilt symptoms appear. However, summer squash can remain vigorous and continue to produce fruit for weeks after wilting occurs.
  • Signs: A common field diagnostic test for bacterial wilt involves cutting a wilted vine close to the stem, rejoining the cut surfaces for a moment, and then slowly pull the cut ends apart. If E. tracheiphila is present, then strands of a white, bacterial slime will ooze from the cut surfaces. Slime can also be observed by placing cut stems in water for 5 to 10 minutes.
  • Management: Management of bacterial wilt relies on primarily on the application of insecticides to control cucumber beetles. The application of insecticides in first few weeks after transplant or seedling emergence is critical. Alternative or supplementary management approaches include perimeter trap cropping, row covers, and biological control.
  • Resources:
    1. Jensen, S. L. 2018. Bacterial Wilt of Cucurbits: Erwinia tracheiphila. Cornell Plant Disease Diagnostic Clinic. Retrieved July 11, 2018.
    2. Keinath, A. P., Wintermantel, W. M., and Zitter, T. A. (Eds.). 2017. Compendium of Cucurbit Diseases and pests(pp. 74-75). St. Paul, MN: APS press.

Bacterial Wilt of tomato is caused by Ralstonia solanacearum, which has a wide host range of more than 200 cultivated plant and weed species in 50 different plant families. Some of the most economically important hosts include tomato, potato, tobacco, and eggplants. The primary inoculum source is infested soil, but other sources also include irrigation water, weeds, farming equipment and operators, and diseased plant material. In the field, bacteria are more concentrated in lower areas with water accumulation.

  • Symptoms: R. solanacearum colonizes and multiplies in the vascular (xylem) tissue of the plant, which causes wilting of infected plants. The first visible symptoms consist of the wilting of the youngest leaves at the end of branches. Wilting will be most visible on hot days and plants may seem to recover at night when temperatures are cooler. Eventually, the entire plant may wilt quickly and dry out leading to plant death. In the field, plants may also become stunted or visually healthy plants may wilt suddenly when fruits are expanding rapidly.
  • Signs in tomato: Cross sections of infected stems may show brown discoloration in the vascular tissue. When a freshly cut stem is suspended in water, a white, milky stream of bacterial cells will flow from the vascular tissue within 3 to 5 minutes.
  • Management: Due to its wide host range and ability to persist in the soil, bacterial wilt is difficult to control. There are no chemical control methods available for bacterial wilt. It is important to use pathogen-free soil, irrigation water, and transplants to exclude primary inoculum sources. Crop rotation and planting cover crops of non-susceptible plants (corn, beans, cabbage, etc.) can reduce soilborne populations of R. solanacearum. Fields should not be over irrigated because excess soil moisture favors disease.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 58-60). St. Paul, MN: APS press.
    2. Vallad, G., Pernezny, K., and Momol, T. 2004. A series on diseases in the Florida vegetable garden: tomato. University of Florida Plant Pathology Department and IFAS Fact Sheet. PP-200. Retrieved April 17, 2018.
    3. Meadows, I. and Henson, M. 2017. Southern Bacterial Wilt of Tomato. North Carolina State University Extension Publications. Retrieved April 17, 2018.

Collar Rot is caused by Alternaria linariae (formerly known as A. solani), which also the pathogen that causes early blight of tomato. Early blight is more commonly observed in the field, but greenhouse tomato seedlings can be affected by collar rot. A. linariae can cause disease occurs in humid climates and semiarid climates with frequent dews that provide enough moisture (≥ 90% relative humidity or greater) conducive for disease development.

  • Symptoms: On seedlings, stem lesions are small, dark, and slightly sunken. As they enlarge, they will form circular or elongated lesions with pronounced concentric rights with light centers. Once the infected seedlings are planted in the field, the lesions will continue to enlarge around the gourd line causing the plants to girdle. If the infection girdles the stem, the seedling will wilt and die.
  • Signs: Mycelia are septate and branched and become dark with age. Conidia (asexual spores) are beaked, muriform (multicelled), dark, 12-20 x 83-117 µm in size, and can be borne singly or chains of two.
  • Management: If it is caught early, then you can build up soil around the stem lesions and the plants can recover. Although there are no early blight resistant varieties, it is recommended to use varieties that are more tolerant to early blight and maintain plant vigor with adequate fertilization to reduce susceptibility. Remove volunteer weeds that cans serve as a source of inoculum. For the latest fungicide recommendations for early blight, please consult the 2018 Southeastern US Vegetable Crop Handbook.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 39-40). St. Paul, MN: APS press.
    2. Meadows, I. 2015. Early Blight of Tomato. North Carolina State University. Plant Disease Fact Sheet. Retrieved May 16, 2018.
    3. Grabowski, M., and Orshinsky, A. 2018. Early Blight of Tomato. University of Minnesota Extension Publication. Retrieved on June 28, 2018.

Cucurbit Downy Mildew is caused by the fungus-like oomycete pathogen Pseudoperonospora cubensis. It infects forty species in twenty genera within the Cucurbitaceae family including cucumber, watermelon, melon, cantaloupe, squash, and pumpkin. High-humidity and moisture, and cool temperatures (~60 ℉) favor disease development. In North Carolina, the disease typically begins in June and lasts throughout the growing season.

  • Symptoms: Leaf lesions appear as angular, yellow to brown spots on the upper side of the leaf. Leaf lesions are restricted by leaf veins. Under favorable disease conditions, the undersides of leaves may be covered in a mass of dark-colored spores which is also called “downy growth”. Downy mildew can be confused with other foliar diseases such as Alternaria leaf blight, angular leaf spot, anthracnose, powdery mildew, and Phytophthora leaf blight.
  • Signs: Under favorable disease conditions, the undersides of leaves may be covered in a mass of dark-colored spores which is also called “downy growth”. However, the color of the masses can range from colorless to gray-brown to deep purple depending on the density and age of the sporangia. Sporulation can be seen in the field with a 20x hand lens. They are most noticeable in early in the morning when dew is present or immediately following rainfall. Under a compound microscope, P. cubensis forms large (20-40 x 14-25 mm in diameter), lemon-shaped sporangia with a conspicuous papilla.
  • Management: Plant early in the season to escape high disease pressure. Do not allow water to remain on leaves for long periods of time as this can favor disease development. Scout plants often and remove infected plants. If possible, plant tolerant varieties and protect the crop with fungicides. For the latest fungicide recommendations for cucurbit downy mildew see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
  • Resources:
    1. Quesada-Ocampo, L. 2013. Cucurbit Downy Mildew. North Carolina State University. Plant Disease Fact Sheet. Retrieved June 14, 2018.
    2. Colucci, S.J. and G.J. Holmes. 2010. Downy Mildew of CucurbitsThe Plant Health Instructor. Retrieved June 14, 2018.

Early Blight of tomato is a damaging disease caused by Alternaria linariae (formerly known as A. solani). The disease occurs in humid climates and semiarid climates with frequent dews that provide enough moisture conducive for disease development. Currently, A. linariae host range is limited to tomato and infection can result in severe defoliation and reduced fruit quality, number, and size.

  • Symptoms: Early blight occurs on leaves, stems, and fruit. Small, brownish-black lesions first appear on older leaves and surrounding tissue may become yellow. Unlike bacterial spot, lesions enlarge rapidly (6 mm or larger) and dark-brown lesions may be encircled by concentric rings. As the number lesions increases, infected plants can become defoliated, exposing the fruit to sunscald. Stem lesions on seedlings are small, dark, and slightly sunken which enlarge to form circular or elongated lesions with concentric rings with light centers. Fruit lesions are large, dark brown to black with concentric rings and may cover the entire fruit.
  • Signs: Mycelia are septate and branched and become dark with age. Conidia (asexual spores) are beaked, muriform (multicelled), dark, 12-20 x 83-117 µm in size, and can be borne singly or chains of two.
  • Management:  Although there are no early blight resistant varieties, it is recommended to use varieties that are more tolerant to early blight and maintain plant vigor with adequate fertilization to reduce susceptibility. Remove volunteer weeds that cans serve as a source of inoculum. For the latest fungicide recommendations for early blight, please consult the 2018 Southeastern US Vegetable Crop Handbook.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 39-40). St. Paul, MN: APS press.
    2. Meadows, I. 2015. Early Blight of Tomato. North Carolina State University. Plant Disease Fact Sheet. Retrieved May 16, 2018.

Phytophthora Crown and Root Rot of cucurbits is caused by Phytophthora capsici. There are several diseases in addition to crown and root rot caused by P. capsici such as damping-off; foliar, petiole, and stem blight; and fruit rot. P. capsici infects a wide range of hosts, including cucurbitaceous, solanaceous, and fabaceous crops, which limits options for crop rotation. Summer and winter squashes and pumpkin are highly susceptible to crown and root rot. The disease is less common in cucumber, melon, and watermelon. When conditions are favorable, the pathogen can cause total crop loss. Disease is favored by warm temperatures (77℉) and wet conditions.

  • Symptoms: Initial symptoms include sudden and permanent plant wilting with out a change in color. Plants may die within a few days of appearance of symptoms or after soil becomes saturated with water from excessive rain or irrigation. Roots and crown may turn light to dark brown and become soft and water soaked. During extended wet periods, leaves may be blighted with dark, water-soaked lesions where infested soil particles were splashed onto the foliage. Fruit may develop large water-soaked spots and rotted in the field or postharvest.
  • Signs: Sporangia of P. capsici are variable in shape (23-35 x 38-60 µm), papillate (has a small, blunt projection), and detach readily from the stalk (caducous). P. capsici is known to produce chlamydospores (thick-walled, asexual overwintering spore) under laboratory conditions, but rarely do so in the field. On fruit, P. capsici produces a white, yeast like growth that contain sporangia, especially under wet conditions.
  • Management: Management of P. capsici is difficult because of wide host range, long-term survival in the soil, and fungicide resistance. Cultural techniques include planting cucurbits in drained fields, using raised plant beds and plastic mulch, clean infested irrigation water, and rotate with nonhost crops. Work in infested fields last and remove diseased fruit offsite. Fungicides may limit crop loss, but the level of management may not be commercially acceptable under conducive disease conditions. For the latest fungicide recommendations for Phytophthora on cucurbits see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
  • Resources:
    1. Keinath, A. P., Wintermantel, W. M., and Zitter, T. A. (Eds.). 2017. Compendium of Cucurbit Diseases and pests(pp. 43-45). St. Paul, MN: APS press.

Septoria Leaf Spot is caused by the fungal pathogen Septoria lycopersici and is widely distributed throughout the world. The disease is particularly severe in areas that are wet and humid for long periods of time. The disease can reduce yield due to loss of foliage, which can either cause fruit to not mature properly or sunscald. Temperatures of 68 to 77℉ favor infection and symptom development.

  • Symptoms: Symptoms will first appear on lower leaves after fruit set. Lesions are circular with dark-brown margins and tan to gray centers with black pycnidia. Lesions may grow to 5 mm in diameter and may be surrounded by a narrow, yellow halo. Lesions can also be on the stems, petioles, and calyx. Fruit infection is rare.
  • Signs: S. lycopersici produces black pycnidia in the center of mature lesions. Pycnidia produce hyaline, filiform conidia up to 10 cells long (3.2x 67.0 µm).
  • Management: There are currently no tomato cultivars resistant to Septoria leaf spot. Crops should be rotated away from tomatoes for 1 to 2 years and susceptible weeds should be removed. Crop debris should be removed, manage irrigation to avoid prolonged periods of leaf wetness, and tomatoes should be staked to improve air circulation. Several fungicides are labeled for tomato to manage Septoria. For the latest fungicide recommendations for Septoria on tomatoes see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 42-43). St. Paul, MN: APS press.

 Southern Blight (also known as southern wilt and southern stem rot) is caused by the soil-born fungus Sclerotium rolfsii. The disease was first reported on tomato, but it occurs on hundreds of other plant species of economically important vegetable, ornamental, agronomic crops. Host crops include bean, cantaloupe, carrot, pepper, potato, sweet potato, tomato, watermelon, and others. High temperatures (77 to 95 ℉), aerobic and moist conditions, and acidic soil favor disease development. In North Carolina, the disease will appear in “hot spots” in fields in early to mid-summer until cooler, dryer conditions prevail.

  • Symptoms: The most common symptom occurs on the stem, which has contact with the soil. A brown to black lesion usually develops on the stem near the soil line. The lesion will develop rapidly and can completely girdle the stem, which will cause a sudden and permanent wilt of all above ground parts. Young plants may fall over at the soil line. If fruit encounters infested soil, then the fungus can easily penetrate the epidermis. Lesions will initially appear as sunken and slightly yellow areas that later become water-soaked, soft, and star-shaped spots. The fruit will collapse within 3 to 4 days and white mycelium and sclerotia can fill the lesion cavity.
  • Signs: Under moist conditions, white mycelium can develop on stem lesions and can sometimes extend several centimeters up the stem of the plant. After a few days, tan to reddish-brown, spherical sclerotia (1 to 2 mm in diameter) can appear on the mat of mycelia. After fruit lesions collapse, white mycelium and sclerotia can fill the lesion cavity.
  • Management: Management of southern blight is difficult when inoculum density is high under conducive conditions for disease development. Avoid fields that have S. rolfsii. Rotate tomato crops with non-susceptible grass crops such as corn, wheat, and barely to reduce inoculum levels in the soil. Modify planting dates to avoid conditions that favor disease development. Remove diseased plants and weed populations. Avoid injuring plants and adopt wider plant spacings (dense canopies increase disease incidence). Inoculum levels can be reduced by burying infected plant debris and sclerotia via deep plowing (at least 20 cm) with a mold-board extension to invert the soil. Plastic mulch and row covers will provide a barrier between plants and the soil and reduces disease severity. For the latest fungicide recommendations for southern blight see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 96-97). St. Paul, MN: APS press.
    2. Meadows, I., and Henson, M. 2017. Southern Blight of Vegetable Crops. North Carolina State University. Plant Disease Fact Sheet. Retrieved June 28, 2018.

Tomato Spotted Wilt Virus (TSWV) is a member of the genus Tospovirus and has one of the widest host ranges of any virus. It is estimated to infect 800 plant species in more than 80 plant families including tomato, pepper, potato, celery, lettuce, legumes, annual and perennial ornamentals, and several weed species. It is transmitted in a propagative manner by seven species of thrips such as western flower thrips (Frankliniella occidentalis) and tobacco thrips (F. fusca).

  • Symptoms: Symptoms can vary among hosts. In most cases, young leaves will turn bronze and later develop numerous, small dark spots. Stunting is also a common symptom and is more severe in young plants. Half or the entire plant maybe stunted. Tomatoes that are infected early may not produce any fruit. On plants infected after fruit set, may produce fruit with chlorotic ringspots. On green fruit, fruit may have slightly raised areas with faint, concentric rings. On ripe fruit, these rings are more obvious and can become red and white or red and yellow.
  • Signs: Virus particles are 80 to 110 nm in diameter and membrane bound.
  • Management: Due to the wide host range of TSWV and its vectors, management of this disease can be difficult. Do not grow ornamental plants in the same greenhouses as vegetable transplants started from seed. An integrated pest management strategy using UV reflective mulches, a plant activator (acibenzolar-S-methyl), and insecticides can provide some control.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 96-97). St. Paul, MN: APS press.
    2. Sherwood, J.L., German, T.L., Moyer, J.W. and D.E. Ullman. 2009. Tomato spotted wiltThe Plant Health Instructor. APS Press. Retrieved May 30, 2018.

Written By

Amanda SchererPostdoctoral Research Scholar (828) 687-0570 (Office) alstraye@ncsu.eduEntomology & Plant Pathology - NC State University

Contributing Specialist

Photo of Inga Meadows, N.C. Cooperative ExtensionInga MeadowsExtension Associate, Vegetable and Herbaceous Ornamental Pathology (828) 456-3943 inga_meadows@ncsu.eduEntomology & Plant Pathology - NC State University
Updated on Jul 19, 2018
Was the information on this page helpful? Yes check No close
Scannable QR Code to Access Electronic Version This page can also be accessed from: go.ncsu.edu/readext?537249