Vegetable Production Update- August 17, 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: Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology) and Amanda Strayer-Scherer (Postdoctoral Research Scholar, Plant Pathology).

Vegetable Production Updates:

  1. Tomato pith necrosis on field tomatoes in experimental plots in Haywood County.
  2. Powdery Mildew on field tomatoes in experimental plots in Haywood County. Powdery mildew of tomato is typically observed in the greenhouse and is not common on field tomatoes. In this case, diseased transplants from an infected greenhouse were planted in the field, which caused the disease to spread.
  3. Bacterial soft rot, a post-harvest disease, was observed on pepper fruit in North Carolina. The fruit was likely damaged, and the disease is considered to be secondary problem.
  4. Spray damage and/or burn was observed on tomato leaves and fruit in Western North Carolina. The symptoms consisted of a speckling, light brown discoloration of issue and was likely caused by the application of copper pesticides.

Upcoming Events: None to report at this time.

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 NC State 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 NC State Extension 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:

Bacterial soft rot of pepper can be caused by bacteria belonging to at least five genera of bacteria including Erwinia, Pseudomonas, Bacillus, Xanthomonas, and Cytophaga. However, Erwinia carotovora subsp. carotovora and E. chrysanthemia are the most aggressive and economically important soft rotters. Strains of Erwinia species do not survive well in fallowed soil and are primarily associated with infested surface water. All these soft rotting bacteria are considered secondary pathogens as they can only infect injured or damaged fruit tissue. Soft rot can occur in the field before harvest and can be spread at harvest and into storage containers.

  • Symptoms: Lesions begin as sunken, light- to dark-colored, water-soaked areas in or around the edge of wounds on the fruit. Lesions will spread rapidly and cause the fruit to deteriorate. Infected fruit will be a slimly and foul smelling.
  • Signs: A whitish, cloudy liquid containing the bacteria may ooze from breaks in plant tissue.
  • Management: Avoid field conditions that favor disease development such as excess nitrogen, excess irrigation, insect stings, or other wounding. Plant on well-drained fields or provide adequate drainage. Do not harvest during rain periods or handling plants when foliage is wet. Clean and sanitize harvest containers and processing equipment daily. Discard decayed fruit and remove free water from fruit by air cooling and drying.
  • Resources:
    1. Pernezny, K., Roberts, P. D., Murphy, J. F., and Goldberg, N. P (Eds.). Compendium of Pepper Diseases: Bacterial Soft Rot (pp. 41-42). St. Paul, MN: APS press.
    2. Pepper Soft Rot. University of Massachusetts Extension Fact Sheets. Retrieved on August 28, 2018.
    3. Kucharek, T., and Bartz, J. 2001. Bacterial Soft Rots of Vegetables and Agronomic Crops. University of Florida Cooperative Extension Service Plant Pathology Fact Sheet. Retrieved on August 28, 2018.

Powdery mildew of tomato is caused by two fungal pathogens, Leveilula taurica and Oidium neolycopersici. L. taurica is commonly found in western regions of the United States and other parts of the world. In contrast, O. neolycopersici is commonly found on tomatoes in California, Connecticut, Nevada, North Carolina, Ohio, and Utah. Both fungal pathogens have a broad host range and can infect several crops and weed species. Infection can occur with little or no free moisture under high humidity. The disease is primarily associated with greenhouse-grown tomatoes, but it can occur on field and garden tomatoes.

  • Symptoms: Symptoms only occur on leaves and initially appear as light green to yellow blotches or sports (1/8 to ½ inches in diameter) on the upper surface of leaves. Spots will eventually turn brown as the leaf tissue dies. Under warm conditions, lesions may expand and become necrotic, which causes the entire leaf to die.
  • Signs: Powdery sporulation (fungal mycelium) can be observed on the upper and lower leaf surfaces under conditions of high humidity.
  • Management: Greenhouses provide conducive conditions for disease development and spread. Remove infected plant and sanitize greenhouse benches and equipment. For the latest fungicide recommendations for powdery mildew of tomato 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. 36-37). St. Paul, MN: APS press.
    2. Vallad, G. E., Roberts, P., Momol, T., and Pernezny, K. 2017. Powdery Mildew on Tomato. Univeristy of Florida, IFAS Extension. Retrieved on August 28th, 2018.

Tomato Pith Necrosis is serous disease of greenhouse and high tunnel tomatoes, which can result in total crop loss. It can also affect field tomatoes. The disease is caused by multiple species of plant pathogen bacteria including Pseudomonas corrugata, P. viridiflava, and Pectobacterium carotovorum. The disease can affect tomato, pepper and several other vegetable and ornamental crops. The disease is favored by high humidity, low light, high nitrogen, and excess irrigation.

Symptoms: Symptoms begin with chlorosis on young leaves and lower leaves will wilt. A dark brown to black, irregular lesion is observed on the stem and will be come necrotic. Several adventitious roots can appear on cracked stem tissue. Severely infected stems may crack or collapse.

  • Signs: If infected stem tissue is cut lengthwise, pith tissue will appear dark in color. This discoloration will be the most evident at the base of the plant but won’t extend into root tissue. In terms of disease distribution in a field or greenhouse, symptomatic plants will occur sporadically or randomly.
  • Management: There are no tomato varieties that are resistant to pith necrosis and pesticides are not effective in managing the disease. Since this is an opportunistic pathogen, the use of good cultural practices is effective in managing the disease such as proper sanitation, use of pathogen-free seed and seedlings, proper nutrition, good soil drainage, and good ventilation in greenhouses. Avoid the use of excess nitrogen and have the soil tested. Reduce humidity by using vents, proper plant spacing, staking and pruning of plants. Do not handle plants when foliage is wet. Remove infected plants and roots to prevent disease spread. Sterilize stakes, ties, and other equipment with 10% bleach or commercial sanitizer.
  • Resources:
    1. Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests (pp. 60-62). St. Paul, MN: APS press.
    2. Grabowski, M., and Orshinsky, A. 2016. Pith Necrosis of Tomato. University of Minnesota Extension. Retrieved on August 28th, 2018.