Jun 30, 2015
Managing bacterial spot in tomato

Bacterial spot is becoming an increasingly devastating disease of tomato in the mid-Atlantic region. Not only can the pathogen directly damage the fruit, severe foliar infection can lead to defoliation reducing both the quality and quantity of marketable fruit. This may be due in part to the increasing frequency of severe weather events that favor disease development as well as shorter rotations between tomatoes due to the economic value of the crop.

The majority of our management tools are focused on preventing and minimizing the primary sources of inoculum through hot-water treating seed, greenhouse sanitation practices, crop rotation, and using new wooden stakes however now that the majority of plants are planted in the field what can be done to prevent and/or minimize potential disease spread:

  • Minimize crop stress by promoting good soil drainage, adequate crop fertility and maximizing air circulation if growing in a high tunnel.
  • Avoid working in the planting when it is wet. It is much easier to spread bacteria within and between plants when they are wet.
  • Separate sequential plantings and work in the youngest planting first. Once the main fruit crop is set, late-season foliar symptoms and potential spread to the fruit are less problematic. Plowing down crop residue soon after harvest is complete will facilitate the decomposition of crop residue and reduce spread to younger successive plantings.
  • Using crop protection products during the season will help manage bacteria on the leaf surface and reduce potential spread. Focus applications early in the season as the flowers begin to die and the immature fruit are less than quarter size. The fruit tend to get less susceptible with age despite the continued spread of foliar symptoms.
    • Fixed-copper based products are still the primary tool and in non-certified organic systems, copper can be tank mixed with mancozeb to enhance the bactericidal effect.
    • Actigard 50WG can help reduce bacterial spot incidence and severity through triggering the plant’s own defense system to produce proteins and other products that enable the plant to suppress the pathogens.
    • Although the mechanism is not well understood, in some trials fungicide programs that included Quintec (quinoxyfen) showed improved disease control although this is not a silver bullet just another option for growers to use during the season.
    • Other products to consider including in a program include Tanos and Regaliaamong others.

There is increasing concern about the potential development of copper resistance within bacterial populations affecting tomato in Pennsylvania as has developed in other production regions in the U.S. The current status of copper resistance in PA is currently not known so with support of the Pennsylvania Vegetable Growers Association and Pennsylvania Vegetable Marketing and Research Board, I am interested in collecting tomato samples with bacterial spot and/or bacterial speck so I can isolate and identify the bacterial pathogen and then evaluate them for their sensitivity to copper. Please contact me at [email protected] or by phone at 814-865-7328 if you are interested in submitting a sample. This season, I am also conducting a fungicide evaluation trial for bacterial spot to provide growers with additional information that they can use to make management decisions.

— By Beth K. Gugin, Associate Professor Vegetable Pathology, Penn State Extension

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