This presentation reviews some effects that different plastic rain cover materials may have on canopy microclimate and fruit quality of table grapes.

1. Effects of Plastic Covers on Canopy
Microenvironment and Fruit
Quality
Matthew Fidelibus
Viticulture & Enology
UC Davis

2. 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

7. Objective
• Determine how green and white-colored plastic
vine covers affect canopy microenvironment, and
yield, quality, and post-harvest spoilage of table
grapes.

8. 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

9. Properties of the
plastics
Reflectivity:
Uncovered : 31%
Green: 31%
White: 53%
Light transmission:
Uncovered: N/A
Green: 70
White: 41

10. Environmental
Measurements in the
canopy
Temperature and relative
humidity (RH*)
Evaporative potential
Condensation

12. Temperature, South-facing fruiting zone, Redglobe, 2011

13. Diurnal temperatures, top center of the canopy, Redglobe, 2011

14. Diurnal temperatures, north-facing fruit zone, Redglobe, 2011

15. Plastic, time of day, and
condensation, Redglobe, 2011
Morning Afternoon
Plastic condensation (ml/cm2)
Green 0.026 a 0.020
White 0.017 b 0.016

16. 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

17. 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

18. 1” Rain 5 Oct 2011

19. Percent clusters with rot, under
different covers, at different times
October 4 October 19
Rot incidence
Covering (% clusters with rot)
uncovered 7b 21
green 8b 21
white 14 a 19
Significance (P>F) 0.04 0.85

20. Cumulative boxes picked per row,
Redglobe, 2011

21. Redglobe berry quality, 4 Oct
Berry Soluble Titratable
weight Berry color characteristics solids 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

22. Redglobe berry quality, 20 Oct
Berry Soluble Titratable
weight Berry color characteristics solids 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

23. 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

24. 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?

25. South-facing fruit zone temperatures, AK, 2012

26. Top-center canopy temperatures

27. North-facing fruit zone temperatures

28. 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)

29. 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

30. Acknowledgements
• California Table Grape Commission
• Steve Vasquez, Kimberley Cathline, Jorge
Osorio