Plastic Rain Covers Can Affect Canopy Microclimate And Fruit Quality

Matthew FidelibusTable grapes are a labor- and material-intensive crop with high annual operating expenses. Therefore, it is important for growers to minimize their risk of crop loss. Precipitation within six weeks of harvest can stimulate the development of rots and molds that may render grapes unmarketable, so many growers of late-season table grapes cover their vines with sheets of polyethylene film.

The films, which are generally about 1 millimeter thick and 100 inches wide, are typically deployed in late August or early September, and installed in such a way that they form an uninterrupted cover along the entire length of the row. At least two different colors of film — green and white — are available.

The green film appears to be more transparent than the white film, but the quantity and quality of light transmitted by either film has not been reported.

Other grape-growing countries — particularly Italy — also use plastic covers, but the timing and method of deployment and the materials used are quite different. In Italy, protection from late-season rains begins at veraison, when colorless transparent polyethylene sheets are attached to frames above the trellising system, with areas between each vine row being left uncovered.

Such covers apparently affect the vine microclimate, as a study showed leaf water potential was increased by the covers, as were variables that contribute to fruit quality, including soluble solids and anthocyanin content. The California covering systems, which consist of films that are thinner, colored, and in direct contact with the canopy, are likely to create a microclimate different than that of Italian systems.

Green and white plastic rain covers on Red Globe table grapes in Fresno, CA. In studies, it appears green covers may delay fruit ripening and both covers may provide some protection from postharvest rots. (Photo credit: Matthew Fidelibus)
Green and white plastic rain covers on Red Globe table grapes in Fresno, CA. In studies, it appears green covers may delay fruit ripening and both covers may provide some protection from postharvest rots. (Photo credit: Matthew Fidelibus)

Studying How Films Affect Grapes In California
I recently conducted a study in late September to characterize the effects the two most common film covers may have on canopy microclimate, vine physiology, and fruit quality.

Red Globe (in 2011) and Autumn King (in 2012) table grape vines were covered with green or white plastic films, or left uncovered. Canopy microclimate, rot incidence, and fruit yield and quality at harvest and after postharvest storage were evaluated. The green film was more transparent and less reflective than the white. The films had little effect on fruit zone temperatures, but the daily maximum temperature in the top center of the canopy of vines covered with green film was consistently 41 degrees Fahrenheit higher than that of vines subjected to other treatments.

Treatment effects on relative humidity (RH) depended on location within the canopy and time of day, but both films consistently reduced evaporative potential under the covers, though not in the fruit zones.

Treatment effects on condensation beneath the films were inconsistent, but South-facing surfaces generally had less condensation than vertical or North-facing surfaces. Approximately 1 inch of rain fell on Oct. 4, 2011, but no rain occurred during the experimental period in 2012.

Green films slightly delayed fruit maturation in 2011, but not in 2012. Films did not affect the number of boxes harvested, or postharvest fruit quality in 2011, but fruit from covered vines had less postharvest rot in 2012 than fruit from non-covered vines, even though significant rain occurred in 2011 but not 2012.

I found the films had consistently different effects on canopy temperature, with the green film causing more heating than the white, but effects on fruit yield and quality were more variable. It appears that the green covers may delay fruit ripening, and both covers may provide some protection from postharvest rots, but additional data is needed to clarify those results. Moreover, the plastics may have other economic impacts such as the time needed to harvest and clean the fruit, which was not measured in this study, but should be considered in future studies.

Topics: , , , , ,

Leave a Reply

Grapes Stories
Grapes
August 26, 2017
Ode to Being a Part-time Farmer [Opinion]
I work with many grape growers in Virginia. Some of them work full time at a single vineyard operation. Many Read More
GenNext Growers
August 8, 2017
Winegrape Society Awards $100,000 in Scholarships
American Society for Enology and Viticulture bestows awards at its 68th national conference. Read More
Grapes
July 7, 2017
California Winegrowers Applaud $5 Million to Battle Disease
Governor approves Pierce’s Disease Control Program money for the first time since 2011. Read More
Grapes
July 3, 2017
Climate Doesn’t Weigh Heavy On Ste. Michelle Wine Estates
While warming trend has been a part of past few seasons, the vineyard is incorporating new technologies to grape growing versus altering production techniques. Read More
Grapes
July 3, 2017
How to Handle Warming Pacific Northwestern Vineyards
The warming temperatures in the Pacific Northwest are well-suited for red winegrape production, but other changes in viticulture practices must be made. Read More
GenNext Growers
June 29, 2017
Cornell Graduate Student Earns Grape Disease Research
Doctoral candidate recognized by American Society of Enology and Viticulture for work studying sour rot pathogens. Read More
Grapes
June 29, 2017
Cornell University Wants You to Name That Grape
Contest to name cold-tolerant variety a seedless ‘Concord’-type berry runs through July 31. Read More
Grapes
June 26, 2017
Washington Grape Grower Battles New Threat
Apples, cherries, and pears are also threatened by Tobacco Ringspot Virus, a pathogen never before seen in Washington state. Read More
Food Safety
June 21, 2017
Organization Seeks Winegrape Exemption Produce Safety Rule
California Association of Winegrape Growers says because winegrapes are grown for processing, they should be exempt from produce safety rule. Read More
Grapes
June 5, 2017
California Winegrowers Award Scholarships to Employees’ Kids
California Association of Winegrape Growers Foundation awards $30,000 in student scholarships. Read More
Grapes
June 5, 2017
Getting to the Bottom of Berry Scarring
It’s a costly defect, but learning what causes berry scarring can help you prevent it. Read More
Grapes
June 3, 2017
Powdery Mildew Management Tips for Vineyards
Follow these suggestions to help reduce disease pressure in your vineyard. Read More
Grapes
June 2, 2017
Cutting Down on Biggest Grape Growing Expense
An automated grapevine pruner hopes may help slash labor costs. Read More
Grapes
June 1, 2017
Organization Now Washington Winegrowers
New name and logo better reflects the evolution of the state’s industry, as more growers have wineries. Read More
Grapes
May 19, 2017
Researchers Still Have a Lot to Learn about Spotted Lanternfly
While some feeding habits have been recognized, there’s still a learning curve with this enigmatic invasive pest. Read More
The Latest
Grapes
September 12, 2017
Heat Wave Leads to Early Winegrape Harve…
Ask any winegrape grower to describe the grape harvest in Sonoma County and you typically hear “harvest time is like Read More
Grapes
September 8, 2017
Spotted Lanternfly Population Large This…
Thanks to mild winter, numbers for the pest are growing, especially in southeast Pennsylvania. Read More
Grapes
August 30, 2017
ASEV Confirms Enologist as President
Washington State University’s James Harbertson to lead American Society for Enology and Viticulture (ASEV) as the 2017-2018 president. Read More
Grapes
August 26, 2017
Ode to Being a Part-time Farmer [Opinion…
I work with many grape growers in Virginia. Some of them work full time at a single vineyard operation. Many Read More
GenNext Growers
August 8, 2017
Winegrape Society Awards $100,000 in Sch…
American Society for Enology and Viticulture bestows awards at its 68th national conference. Read More
Grapes
July 7, 2017
California Winegrowers Applaud $5 Millio…
Governor approves Pierce’s Disease Control Program money for the first time since 2011. Read More
Grapes
July 3, 2017
Climate Doesn’t Weigh Heavy On Ste. Mich…
While warming trend has been a part of past few seasons, the vineyard is incorporating new technologies to grape growing versus altering production techniques. Read More
Grapes
July 3, 2017
How to Handle Warming Pacific Northweste…
The warming temperatures in the Pacific Northwest are well-suited for red winegrape production, but other changes in viticulture practices must be made. Read More
GenNext Growers
June 29, 2017
Cornell Graduate Student Earns Grape Dis…
Doctoral candidate recognized by American Society of Enology and Viticulture for work studying sour rot pathogens. Read More
Grapes
June 29, 2017
Cornell University Wants You to Name Tha…
Contest to name cold-tolerant variety a seedless ‘Concord’-type berry runs through July 31. Read More
Grapes
June 26, 2017
Washington Grape Grower Battles New Thre…
Apples, cherries, and pears are also threatened by Tobacco Ringspot Virus, a pathogen never before seen in Washington state. Read More
Food Safety
June 21, 2017
Organization Seeks Winegrape Exemption P…
California Association of Winegrape Growers says because winegrapes are grown for processing, they should be exempt from produce safety rule. Read More
Grapes
June 5, 2017
California Winegrowers Award Scholarship…
California Association of Winegrape Growers Foundation awards $30,000 in student scholarships. Read More
Grapes
June 5, 2017
Getting to the Bottom of Berry Scarring
It’s a costly defect, but learning what causes berry scarring can help you prevent it. Read More
Grapes
June 3, 2017
Powdery Mildew Management Tips for Viney…
Follow these suggestions to help reduce disease pressure in your vineyard. Read More
Grapes
June 2, 2017
Cutting Down on Biggest Grape Growing Ex…
An automated grapevine pruner hopes may help slash labor costs. Read More
Grapes
June 1, 2017
Organization Now Washington Winegrowers
New name and logo better reflects the evolution of the state’s industry, as more growers have wineries. Read More
Grapes
May 19, 2017
Researchers Still Have a Lot to Learn ab…
While some feeding habits have been recognized, there’s still a learning curve with this enigmatic invasive pest. Read More