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
The harvest bins weren’t necessarily bursting this year in California winegrape country, but the quality was repeatedly described by industry veterans as outstanding. (Photo Credit: George Rose, California Wine Institute)
Grapes
November 27, 2016
Quality California Winegrape Crop This Year
Customary yield combined with remarkable quality, not to mention long-awaited rainfall, made this year a win/win/win. Read More
potato field
Crop Protection
November 21, 2016
Syngenta Announces New Fungicide Product Line
The Miravis brand contains a new active ingredient that is currently pending EPA approval. Read More
A cluster of table grapes, discolored by heat stress. (Photo credit: University of California Cooperative Extension)
Grapes
November 8, 2016
India Requesting Permission To Send Fresh Grapes To The U.S.
Comment period has opened on the request, and a risk assessment is now available from USDA. Read More
EGVM
Grapes
October 31, 2016
An Exquisite Extermination – European Grapevine Moth [Opinion]
We all complain about wasted tax dollars — and rightly so — but a little applause, please, for the eradication of a feared pest. Read More
(Photo credit: Wikimedia Commons)
Grapes
October 25, 2016
New Technology Aims To Develop Climate-Tolerant Grapes
Genomics are being used to help develop winegrape varieties. Read More
lettuce field 14_WR
Crop Protection
October 11, 2016
New Fungicide For Lettuce Growers
Product is proven to control lettuce drop. Read More
Weed science advisor John Roncoroni explains that Roundup doesn't do much for horseweed during a presentation about the use of herbicides in vineyards.
Weed science advisor John Roncoroni explains that Roundup doesn’t do much for horseweed during a presentation about the use of herbicides in vineyards. (Photo credit: University of California Division of Agriculture and Natural Resources)
Grapes
October 1, 2016
Vineyard Weed Control Should Start Now
With harvest ending, weed control might not be top of mind at a lot of vineyards. But it should be, Read More
The Latest
Grapes
December 3, 2016
You Need To Have Flexibility In Your Vin…
Prioritization and compromise are sometimes necessary in a challenging growing environment. Read More
Grapes
December 2, 2016
Study Investigates Savings From Naturall…
After two years on the market, researchers ‘discuss cost-cutting benefits of ‘Sunpreme.' Read More
Grapes
December 2, 2016
Washington Wine Seminar Expands Format
Research-focused sessions to be held across state in conjunction with event in 2017. Read More
Grapes
November 27, 2016
Quality California Winegrape Crop This Y…
Customary yield combined with remarkable quality, not to mention long-awaited rainfall, made this year a win/win/win. Read More
Crop Protection
November 21, 2016
Syngenta Announces New Fungicide Product…
The Miravis brand contains a new active ingredient that is currently pending EPA approval. Read More
Grapes
November 8, 2016
India Requesting Permission To Send Fres…
Comment period has opened on the request, and a risk assessment is now available from USDA. Read More
Grapes
October 31, 2016
An Exquisite Extermination – Europ…
We all complain about wasted tax dollars — and rightly so — but a little applause, please, for the eradication of a feared pest. Read More
Grapes
October 25, 2016
New Technology Aims To Develop Climate-T…
Genomics are being used to help develop winegrape varieties. Read More
Crop Protection
October 11, 2016
New Fungicide For Lettuce Growers
Product is proven to control lettuce drop. Read More
Grapes
October 1, 2016
Vineyard Weed Control Should Start Now
With harvest ending, weed control might not be top of mind at a lot of vineyards. But it should be, Read More
Grapes
September 29, 2016
Vinifera Finds A Home In The Finger Lake…
In a region known for spectacular sights, varieties are making their mark, just ask the team at Sawmill Creek Vineyards. Read More
Grapes
September 26, 2016
Where Site And Growing System Meet In Th…
Vineyard manager uses growing systems to control vigor of winegrape varieties. Read More
Grapes
September 7, 2016
Looking To Italy For New Winegrape Varie…
An Italian viticulturist shares his thoughts about a California region, and what new varieties might thrive in their climate. Read More
Grapes
August 27, 2016
Managing Water In California Vineyards
National viticulture symposium provides insights into estimating vineyard irrigation requirements. Read More
Grapes
August 26, 2016
Model Vineyard Looks To Maximize Concord…
Watching Michigan ‘‘Concord’’ grape growers struggle with stagnant and sometimes declining prices, a team of researchers at Michigan State University Read More
Grapes
August 23, 2016
Deeper Irrigation Method Showing Promise…
A new subsurface irrigation system is showing promise for slashing water usage in vineyards. Many vineyards use drip lines that Read More
Grapes
August 19, 2016
European Grapevine Moth Eradicated From …
Agricultural officials confirm eradication of invasive pest, lift quarantine restrictions. Read More
Grapes
August 10, 2016
The Top 10 Muscadine Grape Varieties For…
UF/IFAS scientists scour the best selections for health, taste, and smell. Read More