Comparison of Trunk Wraps in their Ability to Protect Kiwifruit Vines from Freeze Injury

Abstract

The golden kiwifruit is a new crop to the southeastern United States, with orchards being established across the region. Unfortunately, freeze injury is prevalent due to fluctuating winter temperatures that impact cold resistance of vines. Some vines become injured, developing cracks in their trunks or experiencing a softening of the vascular cambium, both of which reduce vigor and can result in die-back or mortality. Trunk wraps can be used to help regulate temperature fluctuations experienced by kiwifruit vines, so this experiment was designed to test the effectiveness of various materials on kiwifruit vines on an orchard in Reeltown, Alabama. Two studies were performed on one-year-old and two-year-old vines in the winter of 2018-2019, and two more studies were conducted in the same location over the winter of 2019-2020. A spun bound polypropylene row cover (GG-51, Gro-Guard UV®, Atmore Industries, Atmore, AL), was wrapped around vine trunks six times to create the 6-wrap treatment, and twelve times to create the 12-wrap treatment. Polyethylene PVC pipe insulation 2 centimeters thick, fiberglass pipe insulation 2.2 centimeters thick, and white latex trunk paint were used to create the fourth, fifth, and sixth treatments. Data loggers were mounted on vines underneath wraps on vines where wraps were used. At the end of the season, vines were inspected for injury and temperature data were analyzed.

No treatments reduced the amount of damage received by the vines, but the polyethylene treatment increased damage during one study. There were pronounced differences in the temperature retention of some treatments, with the 12-wrap treatment and fiberglass wraps maintaining higher minimum temperatures and cooler maximum temperature than the control during most studies. This is in contrast to polyethylene treatments, which maintained higher minimum temperatures than the control, but exceeded the control by as much as 7°C at maximum temperatures. The effect of wraps was also compared by looking at the amount of time wraps were exposed to very low temperatures (-5°C and -3°C) and very high temperatures (25°C and 30°C). The 12-wrap and fiberglass treatments outperformed the control and the other treatments, with vines receiving these treatments being exposed to both extremely low and extremely high temperatures for shorter durations than the control. Meanwhile, the polyethylene treatment maintained high temperatures under wraps for greater amounts of time than the control. The 6-wrap treatment maintained higher maximum temperatures around the vine trunk than the control, but did not remain as warm as the 12-wrap treatment.

These data imply that while spun-bound polyethylene has some valuable insulative properties, they are most useful when the wrap is applied at greater thickness. Trunk paint has negligible effects and is indistinguishable from the control when comparing temperature and damage. Polyethylene treatments used in this study had a similar insulative capacity to the 6 wrap application of trunk wrap, but the high temperatures it reaches in the daytime are not desirable, so it is less likely to be usable as a trunk wrap. The 12-wrap and fiberglass wraps were the most effective materials tested in the experiment, and have the greatest potential for use as trunk wraps.