A Michigan State University (MSU) study on protected cherry production has recently expanded its research to include a computer-controlled retractable roof structure from Cravo Equipment.

MSU specialist Dr Gregory Lang told www.freshfruitportal.com the study started in 2005 with multi-bay high tunnels to protect crops, and since then it has sought to develop high efficiency orchard training systems to make the most of different expensive covers.

Lang emphasized the need for crop protection by pointing out most arable land in the U.S. was considered unsuitable for sweet cherry production due to several climatic limitations, including a high risk of rain during ripening that causes fruit to crack.

"There is a high risk of damaging cold temperatures during bloom, a high risk of damaging cold temperatures during winter dormancy, and a high frequency of climatic events conducive to bacterial canker infections that can cause flower, branch, and even tree death.

"And, there is a high frequency of warm, humid conditions that prove expensive to control fungal diseases like cherry leaf spot and fruit brown rot."

From analysis of the impacts of the altered environment since 2005, the researchers have found covers can reduce the effects of the elements, lead to higher yields and larger fruit size, create potential for earlier bloom for high value markets, eliminate cherry leaf spot, reduce the incidence of bacterial canker and lower the incidence of Japanese beetles damaging leaves.

On the other hand, under these systems the researchers have found bumblebee pollinators may be needed for optimal yields, there is increased potential for soft fruit if high temperatures during ripening are not controlled, and that there is a higher incidence of powdery mildew.

'X Frame' retractable roof benefits

Lang said the scientists have only recently begun their research into the effects of Cravo's 'X Frame' retractable rooves on cherry crops.

"Retractable roof protective structures require a significantly higher investment than high tunnel structures, so additional crop value must be obtained," he said.

"While our research is just beginning, there are several benefits readily apparent."

He says the main benefit is protection from rain-induced fruit cracking, which however is not always prevented by preventing the fruit's contact with rain. Rain that is shed by tunnel covers or excessive irrigation water can be absorbed by the root system and also lead to cherry cracking.

"Therefore, diversion of rain shed from protective covers must be achieved, generally by modification of soil topography and drainage characteristics.

"The retractable roof protective structures collect all run-off water into roof gutters, channeling it out of the orchard before it even reaches the soil.

"Therefore, it provides the most complete rain-cracking protection possible, eliminating both fruit and root contact with water during rain events, a critical benefit in rainy environments."

The X-Frame retractable roof also has overlap to prevent rain penetration and to help contain heat, while it also has capacity to hold light snowloads.

He says the second benefit is the potential for optimizing temperature control in early spring by using the automated retractable roof, in a bid to promote bloom and leaf development while preventing both excessive heat and damaging cold.

"We are also interested in whether the ability to modulate the opening of the retractable roof panels during pollination may facilitate honeybee, rather than bumblebee, pollinators due to optimized pollination weather and a more natural light spectrum.

"Third, automation is key for optimizing control of temperature and sunlight exposure, while protecting from wind and hail for maximum photosynthesis during fruit ripening to achieve high fruit quality traits, including sugar content and firmness.

"The ability to automatically open and close the roof panels should also promote better red blush development on high value yellow varieties like Rainier."

He adds the automation is also key for controlling sunlight exposure and water relations for maximum photosynthesis during the postharvest summer to build strong flower buds and storage reserves for the following year's crop.

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