Vegetable Production Update-May 25, 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 May 25th Veggie Call: Johnny Coley (Extension Agent, Granville County), Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology), and Gene Fox, virtually (Area Agent, Hyde, Tyrrell, and Washington Counties).

Vegetable Production Updates:

  1. In Granville County, commercial squash producer experienced symptoms that NCSU’s Plant Disease and Insect Clinic (PDIC) suspects is a virus and have ruled out herbicide damage. Grower pulled out affected plants and adjacent plants, and remaining plants appear to be healthy.
  2. A commercial producer in Granville County recently transplanted peppers onto black plastic. About 1/3 of the pepper transplants had damaged, burned stems and/or were killed due to the plants touching the black plastic. However, some of the pepper transplants are recovering and the grower will probably switch to white plastic next year to avoid this problem in the future.
  3. In Rutherford County, tomatoes exhibited symptoms that appeared to be late blight (Phytophthora infestans). Based on morphological characteristics, the causal agent was Phytophthora nicotianae and was not the late blight pathogen. Lesions look very similar to late blight, but P. nicotianae only moves locally (within a field) and is not easily spread by wind and air currents like P. infestans. Grower was advised to put late blight products on (they are effective for all Phytophthora) at least until the weather turns warmer and drier.
  4. A producer in Macon County received pepper transplants from a greenhouse in Southern Georgia. Upon arrival, the transplants had water-soaked, large black spots on some of the leaves (<5%). Trays had been transported on metal, rusty racks and symptoms only appeared on upper and outer leaves that had contact with the metal racks. No plant pathogenic bacteria, such as Xanthomonas or Pseudomonas spp., could be isolated from the tissue. Due to this information, it is suspected that something from the metal racks caused damage on the tissue and a secondary organism has caused the spots. Growers had already started planting and the new growth should be fine.
  5. In Beaufort County, three separate cases of Tomato Spotted Wilt Virus (TSWV) were reported in home garden tomatoes.

Upcoming Events:

  1. Mountain Research Station Field Day on Thursday July 19th, 2018 at 2 p.m. (research updates, trade show, entertainment, and more!).

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: 

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

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 wilt. The Plant Health Instructor. APS Press. Retrieved May 30, 2018, from the APS page on Tomato spotted wilt.