Specialists: Tomato disease reaches Indiana's southern border

June 8, 2010

WEST LAFAYETTE, Ind. - Hoosiers who grow tomatoes in backyard gardens and in commercial operations are urged to inspect plants for signs of a disease caused by a fungus-like organism that could enter southern Indiana, said Purdue University Cooperative Extension Service specialists.

Late blight of tomato has been found in Boone County, Ky., which borders Dearborn, Ohio and Switzerland counties in southeast Indiana, as well as in the Lexington, Ky.-area counties of Fayette and Clark. The airborne disease damaged tomato plants in at least 30 Indiana counties one year ago.

Educators in Purdue Extension county offices are on the lookout for symptoms of late blight in tomatoes already planted and seedlings being sold at retail outlets, said Jim Mintert, assistant director of Purdue Extension for agriculture and natural resources. Educators can assist tomato growers by examining plants and helping them submit samples of suspected infected plants to Purdue's Plant & Pest Diagnostic Laboratory (P&PDL) for testing, he said.

A list of county offices is available at http://www.ag.purdue.edu/extension/Pages/Counties_alpha.aspx

Late blight attacks a tomato plant's leaves and stems. Infected plants develop brown lesions with whitish borders and sometimes discolored fruit.

The disease thrives in cool, moist conditions, said Dan Egel, Extension plant pathologist at Southwest-Purdue Agricultural Center. Late blight spores travel on storm systems, much like Asian soybean rust, he said.

"Spores can be blown to distances of up to 40 miles," Egel said. "They can move from garden to garden or from garden to commercial field. The microorganism that causes late blight is related to algae and produces a spore that is able to swim in the water on a tomato leaf."

Once a plant is infected it takes about a week before symptoms appear to the naked eye, Egel said. By that time plant damage is already occurring, he said.

"Specialized fungicides are the best option for commercial tomato producers to avoid serious crop losses," Egel said. "If you're across the river from Boone County, Ky., it's probably a good idea to start spraying your plants with some of these products."

For more information, visit the P&PDL late blight of tomato page at http://www.ppdl.purdue.edu/PPDL/lateblight.html  or download Purdue Extension publication "Late Blight of Tomato and Potato" at http://www.extension.purdue.edu/extmedia/BP/BP-80-W.pdf

Instructions for sending plant samples to P&PDL for testing can be found online (http://www.ppdl.purdue.edu/PPDL/physical.html), although tomato growers are encouraged to submit samples through county Extension offices.

Indiana's 2009 late blight outbreak was the state's first bout with the disease since 1998. It is believed the disease entered the state on seedlings sold at retail businesses and later planted in home gardens, and then was spread to commercial tomato fields.

The amount of damage caused by late blight to Indiana's 2009 tomato crop is unknown. According to the Indiana Agricultural Statistics Service, the state's fresh market tomato value fell nearly $4 million in 2009 from 2008, to $9.6 million. Indiana's processed tomato market value rose $11.4 million in 2009, to $36.31 million.

Indiana's commercial tomato production totaled 10,600 acres in 2009, up 15 percent from the previous year.

Writer: Steve Leer, 765-494-8415, sleer@purdue.edu

Sources: Jim Mintert, 765 494-8491, jmintert@purdue.edu

                 Dan Egel, 812-886-0918, egel@purdue.edu

Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
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