Vegetable Production Update- August 31st, 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 3rd Veggie Call: Minda Daughtry (Extension Agent, Lee County), Craig Mauney (Extension Area Specialized Agent, Commercial Vegetables and Fruits), Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology) and Amanda Strayer-Scherer (Postdoctoral Research Scholar, Plant Pathology).

Vegetable Production Updates:

  1. Powdery Mildew on cucumber and squash in Western North Carolina.
  2. Reports of corn earworm on sweet corn in Western North Carolina. The infected crops are from three different field containing BT corn from Monsanto. When BT sweet corn is planted late in the season, it can be susceptible to earworm damage.
  3. High tunnel heirloom tomatoes in Western North Carolina had severe damage caused by high soluble salt buildup.
  4. Late blight has been reported on tomatoes in research plots in Haywood County.
  5. Early Blight was seen on field tomatoes in the Piedmont region of North Carolina.
  6. Spider mites have been reported on tomatoes in Western North Carolina.

Upcoming Events: None to report at this time.

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.
    • 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.
    • 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.
    • For early blight, they are focusing efforts on collecting tomato samples with early blight symptoms from commercial fields in North Carolina.
    • 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:

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 (https://content.ces.ncsu.edu/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 16th, 2018 from https://content.ces.ncsu.edu/early-blight-of-tomato

Late blight is caused by Phytophthora infestans and occurs in cooler, humid areas wherever tomatoes are grown. The disease develops rapidly in conditions with high humidity (100%) and temperatures ranging from 18-24 ℃ (64 to 75 ℉).

  • Symptoms: Lesions of late blight on tomato are irregular in shaped, can be water-soaked on the underside of the leaf, and can be tan to gray to dark-brown in color. The disease can affect both fruit and foliage. On fruit, lesions appear brown and irregular.
  • Signs: A whitish to clear mass of spores (sporangia) may be produced on the underside of the leaf lesions under moist conditions but must be viewed with a hand lens or dissecting scope. Sporangia (21-23 x 21-38 µm) are lemon-shaped, multinucleate, and hyaline.
  • Management: Resistant cultivars and a regular spray program are critical for effectively managing late blight. The fungus is air-borne and can travel rapidly throughout a field and to adjacent fields. Scouting regularly for symptoms is critical so that effective fungicides may be deployed immediately. The Tomato Late Blight Disease Fact Sheet includes valuable information on symptoms and recommendations. Also, USA blight website (usablight.org) is a publicly available resource where you can find management recommendations, track where late blight has occurred in the US, and report outbreaks.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 32-34). St. Paul, MN: APS press.
    2. Quesada-Ocampo, L. 2017. Tomato Late Blight. North Carolina State University. Plant Disease Fact Sheet. Retrieved May 25, 2018 from https://content.ces.ncsu.edu/tomato-late-blight

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 (https://content.ces.ncsu.edu/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 14th, 2018 from https://content.ces.ncsu.edu/cucurbit-powdery-mildew
    2. McGrath, M. T. 2017. Powdery Mildew of Cucurbits. Cornell University, Cooperative Extension Fact Sheets. Retrieved June 14th, 2018 from http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_PM.htm