May 28, 2015
Farming like you expect bacterial diseases

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 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 seems to make the most sense is to be proactive and simply learn to farm tomatoes as if you expect bacterial diseases rather than waiting for any of them to be identified in your operation then beginning treatment. Successful management really requires a season-long approach. The list below contains some practices that have the potential to put tomato growers back in front of these diseases.

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 coats are likely to pop off. Also, the hot water directions need to be followed precisely, so stove tops are not a good choice. We’ve got several sets of hot water baths available around the state. Contact your local horticulture educator for locations of the baths.

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 hose ends touch the ground, use disinfecting foot baths at all entrance areas and refresh the solutions regularly, if reusing trays pressure wash them first, then dip into 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. Therefore, 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.

Tanos 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 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; what do you do once harvest begins?

Use a biostimulant

Actigard, Stimplex, Regalia, Fertileader(s), and Greenstim: Actigard is well recognized as an important part of any program managing bacterial diseases in tomatoes. Like many of the other biostimulants, it stimulates the plants own defensive systems. They 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.

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 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 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 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 Penn State Extension Horticulture Educator or send a sample directly to the Penn State Plant Disease Clinic. More information on how to use the Plant Disease Clinic.

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.

— By Steve Bogash, Penn State Extension Educator

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