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Great Lakes Tomato Session

Dr. Mary Hausbeck

David Monks

Dorota Z. Haman

Dr. Mathieu Ngouajio

Dr. Ron Goldy

Bacterial Cancer Control Discussed

The Tomato Magazine
Feburary 2005

GRAND RAPIDS, Mich.-With the discovery of bacterial canker in several Michigan processed tomato fields last summer, growers have been on the alert and are hopeful they can head off any future serious outbreaks.

Mary K. Hausbeck, with the Department of Plant Pathology at Michigan State University (MSU), provided background information on bacterial canker and other diseases during the 2004 Great Lakes Fruit, Vegetable and Farm Market Expo tomato session, held Dec. 7 at the DeVos Place Convention Center in Grand Rapids, Mich.

She was one of five researchers making presentations. Other topics and presenters were:

· Weed Management in Tomatoes, David W. Monks, Department of Horticultural Science, North Carolina State University.
· Irrigation and Fertigation of Fresh Market Tomatoes, Dorota Z. Haman, Agricultural and Biological Engineering, University of Florida.
· Can You Reduce Irrigation Water Inputs While Maintaining High Yield and Quality? Mathieu Ngouajio and Ronald Goldy, Horticultural Department, MSU.

Caused by the bacterium, Clavibacter michiganensis subsp. Michiganensis, bacterial canker causes plant stunting, wilting and fruit spotting, Hausbeck told the group. In 2004, symptoms on the fruit appeared early and became severe in some fields. What worries the tomato industry is the fact that although yield losses vary from year to year, bacterial canker can be a devastating disease.

"Young plants are more susceptible than older plants," the researcher said. "Bacterial canker can be introduced into a clean field via transplants, machinery and wooden stakes or other equipment that has been previously used in an infected field."

Once a greenhouse or field is contaminated with bacterial canker, steps must be taken to assure that future crops remain disease free, she cautioned. If a greenhouse is contaminated, remove all plant material from the greenhouse (including weeds and dead plant tissue on the floor), wash and disinfect floor surfaces, hoses, equipment, et., with a 10 percent solution of bleach or a commercial disinfectant (GreenShield is an example).

Growers with wooden structures such as benches or trays should soak them in a disinfectant such as bleach (10 percent) or GreenShield for a minimum of an hour; preferably, over night.

"A simple washing of wooden surfaces is inadequate because of the cracks and crevices that may allow the bacteria to escape a surface wash," she warned. "Bacteria that overwinter on a wooden surface may be carried to the plants in water droplets next season during the splashing of overhead irrigation."

Growers with contaminated fields should rotate out of tomatoes for at least three years, Hausbeck advised. The bacteria level drops dramatically after the first year of rotation but not enough to insure complete elimination. Any equipment used in the problem field should be washed and disinfected prior to entering a clean field. Equipment and workers should begin work in the cleanest field and finish with the contaminated field.
Applying copper sprays every five to seven days may help reduce the spread of bacterial canker, the researcher said. Under warm temperatures (75 to 90F with rain), however, the use of coppers may be limited as bacteria has a decided advantage under a wet environment.

To avoid spreading the disease, avoid working in a diseased field when it is wet, Hausbeck cautioned. Bacteria may enter the plant through natural openings or wounds created by wind, pesticide spraying or insects. A film of water on the leaf surface allows the bacteria to remain viable and move. If workers are moving within a wet field and creating new wounds on the plants, new infections are likely. If plants have been staked, all stakes should be treated in the same fashion as wooden trays and benches.

During the 2004 season, a study of bacterial diseases (including bacterial canker) was conducted at the MSU Plant Pathology Farm. Researchers looked at 13 treatments, all of which gave improved control over the check. However, because there was theft of fruit from the plot on several occasions the reliability of the yield data is considered limited.

Products tested were: Acrobat 50WP, Actigard 50WG; Amistar 80WG; BAS 55007F 4.17SC, Bravo Weather Stik 6SC, Cabrio 20WG, Dithane 75DF, Kocide 61.4DF, Kocide 2000 54DF, Ranman 3.3SC, Ridomil Gold Bravo 76.5WP, Serenade Max 20WP and Tanos 50WG.

Weed Management Presentation
David Monks of North Carolina State University warned growers that upright weeds like pigweed are capable of reducing jumbo fruit by 30 percent. Such weeds shade tomatoes and compete for nutrients and water, both necessary for optimum crop growth.

"Weeds can also interfere with crop harvest, making it difficult to locate and harvest fruit," Monks said. "Numerous researchers have reported that weed control during the first 35 days of the growing season is most critical to prevent weeds from reducing fruit yield and quality. This time coincides with tomato transplanting through flowering and early fruit set."

Acknowledging that there are many options for controlling weeds in tomatoes, Monks cited the following:

Preemergence Weed Control
Dual Magnum gives excellent control of annual grasses and certain broadleaf weeds such as broadleaf signalgrass, large crabgrass, goosegrass, fall panicum, foxtails, eastern black nightshade, pigweed and groundcherry.

Goal is not registered in tomatoes in Michigan at this time; however, it looks promising in a plasticulture system for tomatoes. It gives preemergence control of certain annual grasses and several broadleaf weeds such as common ragweed, common lambsquarters, galinsoga and pigweed. Based on some of the initial research conducted in the Southeastern U.S., Goal is likely to fit into a system with methyl bromide alternative fumigants in that timing of application is similar to the fumigants and it gives excellent weed control.

Sandea gives excellent preemergence control of broadleaf weeds such as pigweed, common cocklebur, hairy galinsoga, common lambsquarters, wild mustard, wild radish, common ragweed, smartweeds and velvetleaf. It can be applied to the soil surface just prior to laying plastic mulch. It can also be applied after transplanting either over the top or directed between crop rows but at least 14 days after transplanting. Sandea preemergence does not give as effective control of nutsedge as Sandea postemergence.

Sencor gives effective control of many broadleaf weeds including pigweed, common lambsquarters and many others. Care should be used not to incorporate Sencor too deep. It does not effectively control grass weeds. Thus, in a program including Sencor, an option (preemergence or postemergence) should be included in the program that will control grasses.

Treflan gives effective control of most annual grasses and a few small seeded broadleaf weeds such as pigweed. This herbicide must be incorporated to prevent loss through volatilization.

Postemergence Weed Control
Matrix controls certain grasses and broadleaf weeds such as large crabgrass, fall panicum, foxtails, wild mustard, pigweed species and wild radish.
Paraquat (Gramoxone) is a nonselective herbicide that controls most broadleaf weeds and small grasses. As grasses grow, they become more tolerant of paraquat. Crop injury occurs if Paraquat contacts the crop.

Sundea gives effective control of yellow and purple nutsedge, common cocklebur, smartweeds, ragweeds, hairy galinsoga, wild mustard, wild radish, ragweeds, velvetleaf and other weeds. Sandea also has activity on annual sedges, however, control is reduced as sedges mature. It is very safe to tomatoes when applied according to the herbicide label.

Sencor gives very effective control of many broadleaf weeds including pigweed, common lambsquarters, morningglory species and other weeds. It is not effective on nightshades and groundcherries.

Poast, or Select, controls most annual and perennial grasses. Select herbicide also controls annual bluegrass. Grasses must be actively growing for best control. A crop oil concentrate must be used with either herbicide for optimum control. Do not mix either herbicide with other pesticides.
Hand removal gives effective control of most weeds. Weeds should be removed by hand prior to them reaching 3 to 4 inches tall. If weeds are removed later, they should be cut at ground level to prevent disturbance or uprooting of the crop.

For best results, growers should select herbicides or nonchemical methods of control (Hand removal) based on the expected weed problems and follow all instructions on the herbicide label.

© 2005 Columbia Publishing

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