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
Apples & PearsSolve Your Labor Problems From Within
May 26, 2015
Summer is here, which means harvest season is just around the corner. Hopefully you’ll have the crews you need this Read More
Disease ControlPartnerships Key To Healthy Northwest Vines
May 26, 2015
Washington’s grape industry has seen accelerating growth over the past several decades. That momentum is owed, in part, to the Read More
Disease ControlInland Desert Nursery Is Main Source For Washington’s Clean Vines
May 26, 2015
The Judkins family has been in the business of clean grapevines for more than 40 years. Today, their Inland Desert Read More
UF/IFAS developmental biologist Dennis Gray looks at the progress of grapevines in a vineyard.
Crop ProtectionResearcher Using ‘Precision Breeding’ To Create Disease-Resistant Winegrapes
May 20, 2015
Breakthrough would mean significant savings on pesticide and fungicide sprays. Read More
GrapesMatthew Fidelibus To Be Recognized For Extension Work
May 20, 2015
The American Society of Enology and Viticulture (ASEV) recently announced that Western Fruit Grower™ magazine contributor Matthew W. Fidelibus, of Read More
GrapesUSDA Reports 928,000 Total California Grape Acres
May 12, 2015
But Allied Grape Growers’ numbers suggest there are a lot more non-bearing acres. Read More
GrapesAre Robots The Future Of Grapevine Pruning?
May 12, 2015
A new robotic pruner being developed uses cameras to build 3-D images that help it determine where to make pruning cuts. Read More
The Latest
Disease ControlTips For Grapevine Trunk Disease Diagnostics, Preventio…
May 28, 2015
Various pathogens and environmental factors are considered to be major threats to the vineyard’s health. Pathogens are disease-causing organisms such Read More
GrapesDeadline Extended For Crucial Winegrape Disease And Pes…
May 27, 2015
Returned ballots to continue the Pierce’s Disease/Glassy-Winged Sharpshooter referendum must be returned by June 10. Read More
EquipmentThe Benefits Of Vineyard Mechanization
May 27, 2015
Labor accounts for a substantial fraction of the production costs of most fruits, including grapes. Manual harvest is particularly laborious, Read More
Apples & PearsSolve Your Labor Problems From Within
May 26, 2015
Summer is here, which means harvest season is just around the corner. Hopefully you’ll have the crews you need this Read More
Disease ControlPartnerships Key To Healthy Northwest Vines
May 26, 2015
Washington’s grape industry has seen accelerating growth over the past several decades. That momentum is owed, in part, to the Read More
Disease ControlInland Desert Nursery Is Main Source For WashingtonR…
May 26, 2015
The Judkins family has been in the business of clean grapevines for more than 40 years. Today, their Inland Desert Read More
UF/IFAS developmental biologist Dennis Gray looks at the progress of grapevines in a vineyard.
Crop ProtectionResearcher Using ‘Precision Breeding’ To Cr…
May 20, 2015
Breakthrough would mean significant savings on pesticide and fungicide sprays. Read More
GrapesMatthew Fidelibus To Be Recognized For Extension Work
May 20, 2015
The American Society of Enology and Viticulture (ASEV) recently announced that Western Fruit Grower™ magazine contributor Matthew W. Fidelibus, of Read More
GrapesUSDA Reports 928,000 Total California Grape Acres
May 12, 2015
But Allied Grape Growers’ numbers suggest there are a lot more non-bearing acres. Read More
GrapesAre Robots The Future Of Grapevine Pruning?
May 12, 2015
A new robotic pruner being developed uses cameras to build 3-D images that help it determine where to make pruning cuts. Read More
GrapesNew Alternative To Hedging Could Be A Canopy Management…
May 12, 2015
Palissage can reduce lateral emergence in the fruiting zone, while also decreasing disease. Read More
GrapesTips For Finding Vine Balance
April 28, 2015
Vine capacity, size, vigor, and crop load all must be considered to achieve ideal vine balance. Read More
GrapesAssessing And Managing Grapevine Freeze Injury
April 28, 2015
After two consecutive brutal winters, growers in the Northeast and Midwest are working to salvage vines. Read More
drought sign water crisis
Apples & PearsDiversification: A Response To Drought [Opinion]
April 27, 2015
With Governor Jerry Brown’s announcement of mandatory use reductions, the general public in California is getting a wake-up call on Read More
Disease ControlNew Fungicide For Wide Range Of Fruits, Vegetables In C…
April 21, 2015
FMC officially enters biological marketplace with first sales of Fracture fungicide. Read More
GrapesThe Economic Impact Of Grapevine Leafroll Disease
April 17, 2015
Different control strategies are recommended depending on the prevalence of the disease in vineyard blocks. Read More
GrapesTable Grape Commission Awarded More Funding To Study Po…
April 16, 2015
The research will ensure California grape exports continue uninterrupted. Read More
GrapesMeet The Expert: George Zhuang, Viticulturist
April 10, 2015
Zhuang, a new University of California Cooperative Extension farm advisor, plans to focus his research on increasing production with fewer resources. Read More