One consistent theme over the past several years has been the specter of dealing with bacterial diseases in our tomato fields and high tunnels. Bacterial speck, spot, and canker have become regular challenges for tomato growers. In spite of these challenges, it is possible to grow profitable tomato crops even with these challenges hanging over our heads. In general, the practices noted in this article will also help to reduce fungal diseases as well. One tactic that seems to make the most sense is to be proactive and simply learn to farm tomatoes as if you expect diseases rather than waiting for any of them to be identified in your operation then beginning treatment.
Hot Water Seed Treatment: One of the foundations of any program to manage bacterial diseases is to always use tomato seeds that have been properly heat treated. There is an excellent set of instructions in the Ohio State Fact Sheet “Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens, HYG3085-05”. If you decide to treat broccoli seeds, be ready to plant them immediately as the seed coatings are likely to pop off. Also, the hot water directions need to be followed precisely, so stove tops are not a good choice.
- Greenhouse sanitation: Getting your transplants from a reputable source that keeps their transplant production area immaculate and uses hot water seed treatments is a great first step to disease-free fields, tunnels and greenhouses. If you grow your own, practice the highest levels of sanitation in your transplant production areas. Never let your watering hose ends touch the ground, use disinfecting foot baths at all entrance areas and refresh the solutions regularly, if reusing plant trays pressure wash them first, then dip in an approved sanitizing solution, never store cardboard boxes under benches, keep potting media covered between uses, use disinfecting solutions on all work areas and benches between project runs, and keep non-authorized people out of critical production areas.
- Longer rotations: Current recommendations are to stay out of fields that have a history of bacterial infections for at least three years. Even longer is better to ensure that any crop residue that can harbor disease inoculum is thoroughly decomposed.
Replace your used wooden stakes: It is nearly impossible short of kiln drying used wooden tomato stakes to completely disinfect them. Bacteria are very tiny and can penetrate even very small openings in stakes. In addition they can form protective coverings (biofilms) that are very difficult for disinfectants to penetrate. Even a very small population of bacteria can create a new infection. Therefor, it is worthwhile to either replace wooden tomato stakes annually or move to metal “T” posts that can be power washed then dipped in a disinfectant such as GreenShield, peroxide, or bleach.
- Weed Management: Weeds can harbor the same bacteria that infect your tomatoes. This is especially so for weeds in the Nightshade family, but they are far from the only plants that are suspected of harboring bacterial fugitives. Better long term weed management can greatly reduce any disease inoculum.
- Thanos alternated with copper: At least one study from North Carolina found that alternating Mancozeb + copper with chlorothalonil (Bravo and others) + Tanos was highly effective in managing bacterial canker. Mancozeb + copper (ManKocide) has been well documented as effective in managing bacterial diseases in tomatoes, but complete coverage is essential since these are protectants. Once the bacteria are in the plant, they are protected from the exposure to many of these products. The greatest challenge with Mancozeb-based programs is the 5 day PHI; what do you do once harvest begins?
Use a biostimulant: Actigard, Regalia, and MetaboliK HV-1: Actiguard is well recognized as an important part of any program managing bacterial diseases in tomatoes. Like many of the other biostimulants, it stimulates he plants own defensive systems. These materials are best used as part of a preventative program starting early in the season, but have shown some efficacy in keeping a field operational even after one or more bacterial diseases have been identified. It really helps if any diseases are identified early as these are not cures, so scout often and get suspect plants to a lab for proper diagnosis.
- Higher copper coppers: The balancing act between having sufficient copper in forms that are highly active against bacteria and reducing residues on fruit is a constant challenge. However, you must have enough copper in solution to actually help in managing diseases. When working with different products, it is important to keep good notes on how they performed under your production system and conditions to help inform your material choice decisions in the future.
High levels of sanitation: Preventing people, tools, and equipment from moving bacterial diseases between infected plants and fields is vital in managing these diseases. Bacteria ooze out to the edge of leaves and are readily picked up and moved on clothing and equipment. Always work in ‘clean’ areas first, then move on to infected areas or suspect infected areas last. Be sure to pressure wash all equipment after being in fields that are even suspected of having bacterial pathogens. Do the same to tools and boots. It’s worthwhile to change clothing after working in suspect areas. While it is hard to imagine not wanting to start the day in clean clothes, there are workers that wear the same clothes more than one day at a time. Compared to the potential losses from bacterial diseases, providing clean company provided uniforms may be a minor expense.
- Cull hard when necessary, scout often: Scout your fields and plantings often. Remove suspect plants and get any problems accurately identified. If you suspect a bacterial disease, contact your nearest Extension Educator, or ISP Tech crop advisor, or send a sample directly to your nearest pathology laboratory.
- Timing, wait until after the leaves are dry: As noted earlier, bacteria ooze out to the edges of the leaves through hydathodes early in the day. As you work fields tying, spraying, harvesting, and performing other maintenance chores, it is very easy to pick up and move bacteria to non-infected plants. By waiting until the plants are completely dry in the morning, you can reduce spreading bacteria.
One program that worked well in bacterial canker infected fields in 2014: Several clients that work with the author had tomato fields with plants that were positively identified with being infected with Bacterial Canker in 2014 yet they were able to harvest these same fields right through the growing season. The treatment program that was used in these fields consisted of:
- Injecting Regalia at the 4qt/acre rate every other week.
- Foliar applications with Actigard every other week. Actigard can also be injected. This material has a 14 day PHI on tomatoes.
- Alternating foliar applications with Mancozeb + copper with Regalia + copper.
- The application of another biologically-based biostimulant every other week such as MetaboliK SB at planting followed by MetaboliK HV-1 during the season. Do this application on the opposite week as the Actiguard application.
- Keeping plants at their peak nutritionally using biweekly tissue tesing and adjusting the nutrition program as needed.
- Culling infected plants as well as the plants on either side as necessary.
While beating bacterial diseases may not be possible, proactively managing them may be the path to creating a sustainable living situation with them.
- Steve Bogash, Vegetable Crop Advisor / Researcher