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- Researchers Examines Causes
of Micro-cracks in Tomatoes
- By Karen Gentry
Associate Editor
- A physiological problem in tomatoes called shoulder check has been causing yield losses of up to 75% in Southwest Michigan. An all-out research effort supported by Michigan State University’s Project GREEEN aims to find out the reason for these little speckles.
“They’re tiny lines that look like stretch marks,” said Sieg Snapp, assistant professor in vegetable systems at MSU. Snapp spoke to growers and MSU Extension staff during an evening tour at the Southwest Research & Extension Center in Benton Harbor, Mich. on Aug. 13.
“When it shows up it can be devastating,” said Snapp. It can typically reduce marketable fruit of fresh market tomatoes by 50%. She said shoulder checking has gotten worse in the last five years and has also shown up in North Carolina.
Early research led by Mary Hausbeck, MSU associate professor of botany and plant pathology, has ruled out diseases as a cause of shoulder check.
“We are testing if this defect is due to uneven growth, where too high rates of water and nutrients are forced into fruits faster than the epidermis (skin) of the fruit can expand. Water on the epidermis acerbates the problem,” wrote Snapp in a research handout. She compared this process to a balloon bursting. Snapp believes the problem is due to certain fluctuations in the weather. She said that adding calcium and boron seems to be helping, two nutrients that are naturally in tomatoes. Plastic covers forming a small greenhouse also seems to be helping. All research results are preliminary.
“We’re trying to look at pushing their growth,” said Snapp. One way to do this is by using reflective mulch that increases light to grow fruit faster to see if faster growing causes shoulder check. Use of Surround on tomatoes, a clay treatment to reduce heat at the fruit surface doesn’t seem to be helping. She advises growers to avoid condensation on tomato fruit by pruning to enhance air circulation.
During research in the summer of 2000 weather appeared to be related to the amount of fruit defect in all treatments when comparing different harvest dates. Weather monitoring showed more rainfall and leaf wetness events during the period before the Aug. 10 harvest.
The research is also examining cover crops that could improve tomato fruit quality and yield, according to Snapp. The work uses a team approach, with researchers and Extension with varying expertise working together on new mixtures of cover crops to reduce costs to growers. “We hope to minimize fumigation requirements, as well as fertilizers and fungicides required to grow a high quality tomato crop. Typically tomato growers plant rye or wheat every winter after the tomato harvest.”
Researchers are looking at other winter cover crops to help soil health according to Snapp. They are also looking at summer cover crops or crops such as sudan grass and alfalfa, although growers would have to have space to rotate summer crops.
Snapp will speak on “Improving Tomato Fruit Quality” at the upcoming Great Lakes Fruit, Vegetable and Farm Market Expo in Grand Rapids, Mich. in December.
Southwest Michigan growers produce $11 million worth of fresh market tomatoes annually, over 60% of the $16-$18 million produced in Michigan each year.
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