Vegetable Production Update-May 11, 2018

— Written By

From Dr. Amanda 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 May 11 Veggie Call: Nettie Baugher (Area Agent, Chowan and Perquismans Counties), Johnny Coley (Extension Agent, Granville County), Lisa Rayburn (Extension Agent, Onslow County), Amanda Scherer (Postdoctoral Research Scholar, Plant Pathology), and Suzette Sharpe (Research Assistant, Plant Pathology).

Vegetable Production Updates: Overall, there was not a lot to report for this Veggie Call as it is still early in the season.

  1. In Chowan County, cucurbit producers are beginning to get transplants in the ground, but there are no diseases to report. Although not vegetable production related, producers have reported disease in strawberries.
  2. Producers in Granville County are beginning to plant peppers and tomatoes in the field, but no reports of disease.
  3. Report of Bacterial Spot and Early Blight on greenhouse tomatoes in Rowan County. These tomatoes were not destined for the field or to be sold as transplants.

Upcoming Events:

  1. Cabbage Variety Trial Showcase in Pasquotank County Wednesday, May 16 at 7:30 a.m.

Pest News and other Announcements:

  1. Amanda Strayer-Scherer (Postdoctoral Research Scholar, Plant Pathology): 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. Amanda Strayer-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.

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 in 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.