Effects of Plastic Covers on Canopy Microenvironment and Fruit Quality Matthew Fidelibus Viticulture & Enology UC Davis
Justification and importance Table grapes are costly to produce Late-harvested fruit need rain protection Various plastic films provide rain shelter, but they may allow heat and condensation to accumulate Characterizing performance of existing films will help guide and assess the development of new films
Objective Determine how green and white-colored plastic vine covers affect canopy microenvironment, and yield, quality, and post-harvest spoilage of table grapes.
Field study design and layout Green and white vine covers were purchased from commercial suppliers and installed by a commercial grower in Redglobe (2011) and Autumn King (2012) vineyards Whole rows of vines were covered with green or white plastic, or remained uncovered, in a randomized complete block design replicated three times. Covers were installed in September, and kept in place till harvest (November or October) Environmental and fruit quality data collected periodically
Properties of the plastics Reflectivity: Uncovered : 31% Green: 31% White: 53% Light transmission: Uncovered: N/A Green: 70 White: 41
Environmental Measurements in the canopy Temperature and relative humidity (RH*) Evaporative potential Condensation
Temperature, South-facing fruiting zone, Redglobe, 2011
Diurnal temperatures, top center of the canopy, Redglobe, 2011
Diurnal temperatures, north-facing fruit zone, Redglobe, 2011
Plastic, time of day, and condensation, Redglobe, 2011 Morning Afternoon Plastic condensation (ml/cm 2 ) Green 0.026 a 0.020 White 0.017 b 0.016
Condensation at Different Positions and Times of Day, Redglobe, 2011 Morning Afternoon Position condensation (ml/cm2) North 0.025 a 0.019 b Central 0.032 a 0.028 a South 0.009 b 0.008 c
Evaporative potential differed among coverings and positions in the canopy, Redglobe, 2011 Covering South Central North Uncovered 6.47 6.18 A 6.85 Green 6.99 a 4.24 B b 6.92 a White 7.12 a 3.27 B b 6.35 a
1 Rain 5 Oct 2011
Percent clusters with rot, under different covers, at different times October 4 October 19 Rot incidence Covering (% clusters with rot) uncovered 7 b 21 green 8 b 21 white 14 a 19 Significance (P>F) 0.04 0.85
Cumulative boxes picked per row, Redglobe, 2011
Redglobe berry quality, 4 Oct Berry weight Berry color characteristics Soluble solids Titratable acidity Covering (g) Lightness chroma hue (Brix) (g/100 ml) uncovered 15.1 a 35.36 12.10 22.3 14.9 0.40 b green 14.3 b 36.57 12.03 26.8 15.0 0.42 a white 14.2 b 35.36 11.35 24.6 14.9 0.41 ab Significance (P>F) 0.03 0.10 0.18 0.17 0.93 0.07
Redglobe berry quality, 20 Oct Berry weight Berry color characteristics Soluble solids Titratable acidity Covering (g) Lightness chroma hue (Brix) (g/100 ml) uncovered 15.4 32.37 10.42 16.2 15.7 0.37 ab green 15.6 32.15 10.59 17.3 15.2 0.38 a white 15.4 33.02 10.59 16.9 15.5 0.35 b Significanc e (P>F) 0.97 0.30 0.95 0.55 0.28 0.04
Redglobe postharvest quality, 2011 Days in cold storage 33 46 78 33 46 78 Covering Percent clusters with rot Visual appearance score uncovered 28 68 100 1 2.4 3.0 green 19 67 100 1 2.4 3.0 white 15 53 100 1 2 2.9 Significance (P>F) 0.17 0.16-0.75 0.19 0.38
Summary of 2011 findings, Redglobe Green plastic more transparent & less reflective than white; increased peak canopy temps by 5 C Greatest condensation in morning and under vertical or north facing surfaces Both plastics reduced evaporative potential and slightly delayed fruit maturity Maybe some protection from postharvest rot?
South-facing fruit zone temperatures, AK, 2012
Top-center canopy temperatures
North-facing fruit zone temperatures
RH, South Fruiting Zone
RH, Top Center
RH, North Fruiting Zone
Fruit quality, Autumn King, 2012 No treatment effects on berry weight, Brix, ph, or TA No treatment effects on field assessment of rot After 1 month post harvest storage, fruit from uncovered vines had twice as much rot as fruit from covered vines, regardless of plastic color (40 vs 20% of clusters with some rot)
Overall summary Green plastic transmits more light than white, resulting in higher peak temperatures Condensation worst in the morning, under top & north-facing surfaces; variable differences between plastics Both plastics reduce evaporative potential in canopy but not fruit zone Both covers may slightly delay fruit maturation Covers appear to reduce post harvest rots
Acknowledgements California Table Grape Commission Steve Vasquez, Kimberley Cathline, Jorge Osorio