Bacterial Disease Management in Vegetables

Due to the limited availability of in-season bacterial disease management tools, the most effective management strategies are preventative and focus of reducing the amount of initial inoculum which is typically introduced through planting contaminated seed and transplants. Accordingly, the first line of defense is to use pathogen-free seed and transplants. Many bacterial pathogens are capable of surviving both on and inside the seed. If you purchase transplants, check with your transplant supplier to make sure they have a vigorous greenhouse sanitation program that includes many of the guidelines mentioned below.

If you are growing your own transplants, sodium hypochlorite seed treatments are effective at surface disinfesting seed however they will not effectively manage any bacteria surviving inside the seed and the addition of a surfactant is necessary to ensure that the active ingredient comes in contact with the seed surface. Hot water seed treatments have been shown to be effective at reducing bacterial populations both on and in the seed. Some seed companies offer hot water treatment as an option. Keep in mind that varieties and seed lots can vary in their sensitivity to being hot water treated and often there is a fine line between controlling the pathogen and harming the seed if proper procedures are not followed. To learn more about hot water seed treatments, a hands-on pre-convention workshop is being offered on Monday January 30, 2012 before the Mid-Atlantic Fruit and Vegetable Convention at the Hershey Lodge and Convention Center in Hershey, PA. Learn about how-to hot water treat seed and its’ rationale; practices that limit the development and spread of bacterial pathogens in transplant production as well as in the field and an overview of the epidemiology of bacterial pathogen emphasizing tomato. Participants will be given the opportunity to practice treating seed and will make seed drying racking that they can take home for future use.

The cost to attend this ½ day workshop is $25. Contact Bill Troxell by phone at (717) 694-9536 or by email at pvga@pvga.org to register. Information about the 2012 Mid-Atlantic Fruit and Vegetable Convention can be found at www.mafvc.org.

Be sure to clean and disinfect all greenhouse surfaces including tables, benches, floors, hoses, containers, etc using a bleach solution (1 part bleach to 9 parts water) (some growers have had success using Greenshield and ZeroTol); even if you did not have any problems with bacterial diseases this year. Maintain a weed-free greenhouse. Many pathogens and insect vectors can survive on weed hosts and then move to into to transplants. Scout the greenhouse regularly for disease symptoms and remove any diseased plants immediately. If within a flat, then remove the entire flat. Minimize leaf wetness by watering early in the day. Keep in mind that transplants that appear to be healthy can still harbor high population of bacterial pathogens and that it is easy to move the pathogens around during the course of regular greenhouse activities.

In addition to maintaining a rigorous sanitation program, a regular bactericide spray program consisting of applications of copper hydroxide (equally as effective as streptomycin sulfate) can effectively control bacteria on the surface of the transplant (check the labels for rates and proper use on greenhouse crops). However, very little control can be obtained once the bacteria are inside the transplant so again, prevention is the key.

When selecting a field, chose fields that have been rotated out of tomatoes for at least two years or more to allow the soil microorganisms to thoroughly decompose any crop residue. The bacterial canker pathogen can survive in the field as long as there is infected crop debris. Burying the crop debris will facilitate faster decomposition then allowing it to remain on the surface. Also when possible, maximize the distance between this year and last year’s fields and make sure to implement a good weed management program that includes the removal of any volunteer tomato plants. One commonly overlooked source of the pathogen is planting stakes. It has been well documented that the bacteria can survive for over 10 months in the cracks and crevices of stakes. The use of new stakes each season is best however, if not cost-effective, then a make sure to sanitize them in a bleach solution for at least 15 minutes to allow the water to saturate the wood. Refresh the bleach solution often to minimize of the binding of the sodium hypochlorite with any organic debris in the water.

In the field take measures to minimize the duration of leaf wetness using drip irrigation or by restricting the use of overhead irrigation to early in the day. This allows the leaves to dry completely before evening dew forms. This will also aid in managing other bacterial and fungal diseases as well. Avoid working in the field when the plants are wet to limit plant to plant spread. Always work in clean fields first before moving into infected fields and clean tools, equipment and personal clothing often when moving between clean and infected fields.

Once planted in the field, there are few management options available for bacterial diseases of vegetables besides implementing a standard spray program that includes copper-based bactericides to help reduce the spread of bacterial pathogens and often their likelihood of success can be limited especially when the environmental conditions are in favor of the pathogen (high moisture, high relative humidity and warm temperatures 75 to 90°F). So focusing on prevention through sanitation NOW is the most effective way to reduce your chances of seeing bacterial diseases in your crops next year. Even if you do not have a problem currently, initiating an integrated management program focusing on prevention through sanitation will help ensure a bacterial disease-free crop in the future!