Vegetable Production Update- August 3, 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 August 3 Veggie Call: Craig Mauney (Extension Area Specialized Agent, Commercial Vegetables and Fruit) and Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology).

Vegetable Production Updates:

  1. Downy mildew was reported on cucumbers, cantaloupe, and butternut squash in sentinel plots at the Mountain Research Station in Haywood County. Downy mildew was also reported on cucumbers in sentinel plots in Henderson County. Basil downy mildew has also been reported in northern South Carolina. See the Pest News alert for more information.
  2. Southern blight was reported on cucurbits, peppers, and tomatoes in Western North Carolina. In most cases, southern blight has been reported in fields that were not fumigated.
  3. Powdery mildew was reported on squash in Western North Carolina.
  4. Phytophthora root rot was reported on peppers in Western North Carolina.
  5. Producers in three counties in Western North Carolina have reported Pole Beans without pods. This could be due to heavy rains which can cause flower blossoms to drop and reduce pollination/lack of pollinators.
  6. Magnesium deficiency was reported on cucumbers in Western North Carolina. Magnesium deficiencies are common in sandy soils with low PH or with low concentrations of magnesium (less than 70 ppm). Symptoms will appear a few weeks before harvest, when vines are rapidly growing, and fruit begin to enlarge. A gray-green discoloration of the interveinal tissue will occur on the crown leaves, which will expand and become brown or tan over time. In severe cases, the leaf tissue will disintegrate. For management, test soils regularly and amend with dolomitic lime when appropriate.
  7. Spider mites have been observed on high tunnel green/bush beans and hot peppers in Western North Carolina.
  8. Two fields in Western North Carolina have reported a heavy infestation of aphids on leafy greens. Infestation was severe due to lack of scouting.
  9. Although not a vegetable production issue, Alternaria has been reported on sunflowers in Western North Carolina.

Upcoming Events:

  1. 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):
    1. 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. REMINDER TO AGENTS: Sign up for NCSU’s Pest News and Pest Alerts so you will know when late blight and downy mildew appear in your county(ies) and to stay updated on other production issues.
  1. 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 Veggie Call:

Basil Downy Mildew is caused by the fungus-like, oomycete pathogen Peronospora belbahrii. The pathogen prefers cool temperatures (~60°F), high-humidity, and moisture (6-12 hours of moisture which usually occurs as morning dew, rain, or overhead irrigation). In North Carolina, the disease typically begins in June and will last throughout the growing season. Spores can be transported from state to state via air currents and the pathogen can also be seedborne.

  • Symptoms: Yellowing or browning of leaves will occur and can be confused with nutritional problems. However, the underside (“downy” side) of infected leaves will be covered with dark, brownish-black to black spores.
  • Signs: Typically, dark spores can be observed on the underside of infected leaves without a microscope or hand lens. Sporangiophore structures bearing sporangia can be observed using a dissecting microscope.
  • Management: The use of pathogen-free seed is recommended to prevent the introduction of the disease into an operation. Remove infected plants. Reduce moisture by avoiding overhead irrigation, water early in the morning to allow foliage to dry and increase air circulation between plants by using adequate spacing. Some varieties such as red basil, Thai basil, lemon basil, lime basil, and spice basil are less susceptible. For the latest fungicide recommendations for basil downy mildew see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
  • Resources:
    1. Quesada-Ocampo. 2015. Basil Downy Mildew. North Carolina State University. Plant Disease Fact Sheet. Retrieved July 26, 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.

 Phytophthora Crown and Root Rot of pepper (also known as Phytophthora Blight) is caused by the fungus-like oomycete pathogen Phytophthora capsici. P. capsici has a broad host range, which includes bell pepper, hot pepper, tomato, snap bean, lima bean, and most cucurbits. Disease development is favored by excessive rainfall or overhead irrigation, saturated soils, and warm temperatures (75 to 90 °F).

  • Symptoms: P. capsici causes a root and crown rot of pepper and distinctive black lesions on stems. Under wet conditions, root infection will cause the plant to wilt and collapse. Crown lesions will be dark brown and will cause the stem to girdle resulting in plant death. Under rainy and highly irrigated conditions, infested soil can be splashed onto leaves and fruit. Fruit symptoms consist of water-soaked areas that can be covered with a white powdery to cottony mold.
  • 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.
  • Management: When possible, plant resistant pepper varieties. Manage soil moisture by planting in fields with good drainage and even terrain. Planting raised beds on well-drained sites can reduce disease incidence. Do not use infested surface water (ponds or creeks) for irrigation. Avoid overhead irrigation, especially after fruit set. Remove infected plants and fruit. Do not leave cull piles in the field or near irrigation water sources. Rotate with crops such as cereals that are not a host for P. capsici.
  • Resources:
    1. Quesada-Ocampo, L. 2015. Phytophthora Blight of Peppers. North Carolina State University. Plant Disease Fact Sheet. Retrieved August 8th, 2018.
    2. Pernezny., K., Roberts, P. D., Murphy, J. F., and Goldberg, N. P (Eds.). Compendium of Pepper Diseases (pp. 17-18). St. Paul, MN: APS press.

 Powdery Mildew is caused by the fungal pathogens Podosphaera xanthii and Erysiphe cichoracearum. Disease can occur on all cucurbit crops. However, due to the incorporation of resistance genes, most commercial cucumber and melon cultivars are less susceptible. High-humidity (50-90%), moderate temperatures (68 to 80 ℉), dense foliage, and low light conditions favor disease development. However, dry conditions favor colonization, sporulation, and dispersal of the pathogen.

  • Signs and Symptoms: White, powdery fungal growth first appears on older or shaded leaves and on the underside of leaves. Yellow spots may form on upper leaf surfaces opposite of powdery mildew colonies. The white, powdery growth can also appear on stems and petioles. Infected leaves will senesce (deteriorate) early, and fruit yield and quality can be affected. Due to plant stress induced by powdery mildew infections, speckling of fruit can occur in some cucurbits.
  • Management: Provide adequate spacing between plants and remove any debris, weeds, and volunteers that can harbor the pathogen. When possible, the use of resistant cultivars is recommended. Fungicides should be applied to protect the crop from infection. For the latest fungicide recommendations for cucurbit powdery mildew see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
  • Resources:
    1. Quesada-Ocampo, L. 2015. Cucurbit Powdery Mildew. North Carolina State University. Plant Disease Fact Sheet. Retrieved June 14, 2018.
    2. McGrath, M. T. 2017. Powdery Mildew of Cucurbits. Cornell University, Cooperative Extension Fact Sheets. Retrieved June 14, 2018.

Southern Blight of Cucurbits is caused by the soilborne fungus Athelia rolfsii (syn. Sclerotium rolfsii). The disease typically occurs in tropical to subtropical regions and warm, temperate regions. Disease development is favored by warm, moist conditions. Cantaloupe and watermelon fruit seem to be the most susceptible to southern blight.

  • Symptoms: Infections is normally limited to fruit and vine tissue that has contact with the soil. Initial yellowing and wilting of individual vines will occur. The pathogen causes a watery soft rot on fruit.
  • Signs: On fruit tissue in contact with the soil, white mycelium and tan to reddish-brown sclerotia (1 to 2 mm in diameter) will appear on tissue that has contact with the soil. White mycelia and brown sclerotia will be present on the stem.
  • Management: Management of southern blight is difficult when inoculum density is high under conducive conditions for disease development. Deep blowing 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. Liming the soil to raise pH to about 7.0 may also help to control southern blight. Avoid planting cucurbits after a crop in which southern blight was present. Rotate host crops with non-susceptible grass crops such as corn, wheat, and barely to reduce inoculum levels in the soil. Managing the disease with fungicides may not be practical due to costs and target placement. 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. Keinath, A. P., Wintermantel, W. H., and Zitter, T. A. (Eds.). 2017. Compendium of Cucurbit Diseases and Pests (pp. 107-108). 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 August 8, 2018.

 Southern Blight of Pepper is a destructive disease of peppers grown in warm humid regions and is caused by the soil-born fungus Sclerotium rolfsii. The pathogen infects at least 500 species in 100 plant families including vegetable and ornamental crops. 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 pathogen attacks the parts of the stem that are close to the ground. It causes the entire plant to turn yellow and wilt. The stem will turn brown above and below the soil line and decay. Pepper fruit that touch the soil can become infected. Fruit lesions are water-soaked and filled with mycelia and sclerotia.
  • 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 or about the size of a cabbage seed) 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. Do not plant infected transplants into the field. Rotate host 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. Black 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. Pernezny., , K., Roberts, P. D., Murphy, J. F., and Goldberg, N. P (Eds.). Compendium of Pepper Diseases: Southern Blight (pp. 20-21). 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 August 8, 2018.

Southern Blight of Tomato (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 comes into contact with 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 28th, 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 Aug 9, 2018
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