Farming Like You Expect Bacterial Diseases

Bacterial speck, spot and canker have become regular challenges for Pennsylvania and Mid-Atlantic tomato growers. In spite of these challenges, it is possible to grow profitable tomato crops in this region. One tactic that makes sense is to be proactive and simply learn to farm tomatoes as if you expect bacterial diseases rather than waiting for them to be identified in your operation before beginning treatment. Successful management requires a season-long approach. The list below contains some practices that have the potential to put tomato growers ahead of the disease curve.

Hot Water Seed Treatment

One of the foundations of any program to manage bacterial disease 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, HYG-5818". Hot water directions need to be followed precisely, so stove tops are not a good choice. Penn State Extension has several sets of hot water baths available around the state. Contact your local horticulture educator for the locations of the baths.

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 by implementing these best practices.

• Never let your hose ends touch the ground
• Use disinfecting foot baths at all entrance areas.
• If reusing trays, pressure wash them first and then dip them into an approved sanitizing solution
• Never store cardboard packing boxes under benches
• Keep potting media covered between uses
• Use disinfecting solutions on all work areas and benches between project runs
• Keep non-authorized people out of critical production areas

Preventing people, tools, and equipment from moving bacterial diseases between infected plants and fields is vital to managing these diseases. Bacteria ooze out to the edges 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 who wear the same clothes more than one day at a time. Compared to the potential losses from bacterial diseases, providing clean company, company-provided uniforms may be a minor expense.

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 harbors disease inoculum is thoroughly decomposed.

Replace Used Wooden Stakes Every Year

It is nearly impossible - short of kiln drying - to completely disinfect used wooden tomato stakes. 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. Therefore, it is worthwhile to either replace wooden tomato stakes annually or move to metal "T" posts that can be power washed and then dipped in a disinfectant such as GreenShield, peroxide, or bleach. When using these products, be sure to follow the labeled directions for the correct rate.

Cull Hard When Necessary, Scout Often

Scout your fields and plantings often. Remove questionable plants and get any problems accurately identified. If you suspect a bacterial disease, contact your nearest Penn State Extension Horticulture Educator or send a sample directly to the Penn State Plant Disease Clinic. Use this link for information on how to use the Plant Disease Clinic.

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.

Biostimulants

Plant biostimulants prompt the plant to become more efficient at nutrient uptake and stress tolerance. Actigard, LifeGard, Stimplex, Regalia, and Greenstim are examples of biostimulants. Regalia is well recognized as an important part of any program managing bacterial diseases in tomatoes. Like many biostimulants, it encourages the plant's defense systems. Biostimulants are best used as part of a preventative program starting early in the season, but they have shown some efficacy in keeping a field operational even after one or more bacterial diseases have been identified.

Not All Coppers are the Same

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. There are reports that some strains of bacterial spot and speck have resistance to some forms of copper. When working with different products, it is important to keep good notes on how they performed and the conditions applied to help inform your material choice decisions in the future.

Using Pesticides

In general, to suppress bacterial disease, alternate mancozeb + copper with chlorothalonil (Bravo and others) + Tanos in field tomatoes. Mancozeb + copper (ManKocide) has been well documented as effective in managing bacterial diseases in tomatoes, but coverage is essential since these are protectants. Once the bacteria are in the plant, they are protected from exposure to many of these products. The greatest challenge with mancozeb-based programs is the 5-day PHI. Serenade ASO is labeled for bacterial disease on tomato and may be an option for greenhouse and organic producers.

Timing, Wait Until 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 in fields tying, spraying, harvesting, and performing other maintenance chores, it is very easy to pick up and move bacteria to non-infected plants. Waiting until the plants are completely dry can reduce the spread of bacteria.

While beating bacterial diseases may not be possible, proactively managing them may be the path to creating a sustainable situation.