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Fearsome foursome of tomatoes

Greenhouse tomato growers should watch out for the "fearsome foursome," according to cautions from experts at an LSU AgCenter seminar. LSU AgCenter researcher Randy Sanderlin discussed those four things greenhouse tomato growers need to be on the lookout for — gray mold, tomato spotted wilt virus, damping off and powdery mildew — during the 7th annual Greenhouse Tomato Seminar held in Shreveport.

All of those potential problems can be avoided with the proper care, said Sanderlin, who is research coordinator at the LSU AgCenter's Pecan Research-Extension Station and one of the AgCenter faculty members involved in research on growing tomatoes in greenhouses.

"Gray mold is public enemy No. 1 in greenhouse tomatoes," Sanderlin said. "It can get in a plant at stem wounds after pruning and cause the plant to wilt. The fruits can also be infected."

Some steps to take to manage gray mold include making sure the greenhouse is clean and using environmental manipulation such as keeping the relative humidity below 90 percent, keeping the air circulating and using bottom heat instead of top heat to reduce the relative humidity at the plant's surface. Using chemicals such as fungicides to prevent new infections is another step Sanderlin talked about.

The tomato spotted wilt virus is another culprit that can attack greenhouse tomatoes. To control this virus, growers have to keep thrips out of the greenhouse, as well as keep weeds cleared away from the around the house, Sanderlin advised said.

Other things to look out for are damping off, which is caused by pythium, and powdery mildew, Sanderlin said.

Greenhouse tomato growers should also keep houseplants out of their greenhouses, Sanderlin cautioned.

"Some people are tempted to put houseplants in the greenhouses with the tomatoes during the winter," Sanderlin said. "This is something that should not be done. Houseplants could attract aphids, which could infect the tomato plants and cause more problems."

Learning how to control diseases that can ruin a greenhouse tomato crop is just one reason Rollin and Sandra Miller attended the seminar. The Millers of Brooksville, Miss., were just two of about 50 people from Louisiana, Mississippi and Texas who attended the seminar. The couple said they are thinking about getting back into the greenhouse tomato business after being out of it for about 25 years.

"We wanted to learn about the new technology and techniques before we got back into it," Rollin Miller said. "Some Mississippi growers recommended we attend this seminar so that we could have some of our questions answered."

"If we had had something like this back when we first started, we would've been better off," Sandra Miller said.

In addition to Sanderlin's lecture, other information provided at the seminar came from H.Y. Hanna, a researcher at the LSU AgCenter's Red River Research Station in Bossier City, La. Hanna talked about a recent trip he took to Canada where he learned some of the techniques used in greenhouses there.

"No contact with the ground is essential for growing good greenhouse tomatoes," Hanna said. "In Canada, we saw where they used raised gutters to grow their tomatoes."

Using a soil-less medium is another step to take in growing greenhouse tomatoes, Hanna said. Media that can be used include rockwool, pine bark and perlite.

Hanna said he recently conducted a test involving rainwater and tap water to determine the effects of the two on plant yield and fruit quality.

"Water quality is a major factor in growing greenhouse tomatoes," he said. "By conducting this test, I found rainwater is better for the tomatoes than tap water."

In addition to growing media and water, Hanna also explained using a floor heating system warms the plants' roots better, and he said using a white plastic cover on the greenhouse floor can double the light that goes to the plants. He also said new growers should start out growing a spring crop because it is "a moneymaker, there is more daylight for the crop, spring tomatoes are more flavorful and they are easier to grow."

Rick Story, an LSU AgCenter entomologist from Baton Rouge, La., gave a lecture on insect control for greenhouse tomatoes. Story warned that insecticides labeled for use in fields may not be suitable for use in greenhouses.

"Check the label," Story said. "You shouldn't use a product in a greenhouse unless the label specifically states it is suitable for use in greenhouses."

Insecticides mixed with water should be used immediately, Story said, adding that the pH level of the water should be between 5.5 and 6.5 for the insecticide to work effectively.

After the tomatoes have been grown and picked, they must be cared for until they are eaten. David Picha, a horticulturist with the LSU AgCenter in Baton Rouge, spoke about post-harvest care of tomatoes.

"Tomatoes are a very highly perishable crop," Picha said. "All of the money that is put into growing them could be lost if the tomatoes are not taken care of after they are picked."

To insure tomatoes bring the highest price at the market, Picha said to harvest them at the proper maturity stage. He also said growers can maximize the tomatoes' market life by storing them at 55 degrees F, keeping the relative humidity of the storage area at 90 percent and applying waxes, if necessary.

For more information on growing greenhouse tomatoes or other crops, as well as information on topics ranging from money and business to youth development, go to

A. Denise Coolman writes for the LSU AgCenter. (318–366–1477 or

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