Others may care to read of (and comment on?) my experience with cold injury to the Russian apple rootstock, Bud 54-118. Bud 54-118 is marketed by the shortened name, Bud 118 in the USA, although Bud 118 is the proper name of a different rootstock in the Budagovsky series and is not available in the USA (Loren Tukey, personal communication, 1996). Bud 54-118 is considered very cold hardy in Russia and northern Europe. It is semi-vigorous, roughly comparable in vigor to MM 111.
In early April 2008, in a 15 year old one-acre block of Macoun and Mutsu apples (302 trees/acre) grafted at 5 feet above ground to young trunks of either Bud 54-118 or Cortland on Polish #1 (Cortland/P1), I discovered long (1-4 feet), deep vertical cracks in trunk bark of some trees on Bud. Cracks, frequently 2 or 3 per tree, were in the rootstock portion of the trunk, below the fruiting variety. Bark along crack edges was nailed down, and wounds were covered with Doc Farwell’s “Seal and Heal.” Over the next several weeks more cracking became evident, and was similarly treated. This injury was found only on the Macoun/Bud combination; none was present on Mutsu/ Cortland/P1, or Macoun/Cortland/P1. Trunkbark cracks were more common on the south half, but similar cracks could be found on the shaded side. No bark cracking was found in the Macoun portion of the trees.
By the end of the2008 growing season, about a dozen trees were obviously dead, or had one or more dead scaffolds. Many of the remaining Macoun/Bud trees dropped foliage before, during, or soon after harvest. Affected Bud trees have extensive areas of dead cambium and loosening or missing bark. Nailing and painting was of minimal or no benefit. At this time it appears that 25-50% of the trees on Bud will be lost. Macoun/Cortland/P1 and Mutsu/Cortland/P1 show no similar damage, although several trees of each variety have mostly minor “southwest sunscald’ (dead bark) extending not more than 18 inches above ground level.
Below are my current interpretations of these observation; but first, some notes on conditions that could have contributed to the injury.
(1) The winter of 2007-2008 was relatively mild at my site in Connecticut, with near-zero F temperatures only on January 3 and 4 (2 and 4F), February 11 (7F), and February 29 (5F).
(2) All trees in the block were pruned between January 29 and February 9.
(3) Snow covered the ground at the times of the low temperatures, and mostly clear skies prevailed each of the days immediately prior to the four low temperatures.
(4) All trees on Bud were grafted much higher on the rootstock than is typical in commercial orchards and this exposed the Russian stock to air temperatures and warming sunlight a full 5 feet above ground.
(5) The P1 rootstocks were grafted low, to Cortland, and these young Cortland trees were then grafted to Macoun or Mutsu at 5 feet above ground in the year following transplant from nursery to orchard. No Cortland branches were allowed to develop. The Corland/ P1 graft union was buried beneath the soil line when trees were set in the orchard….enabling scion-rooting of Cortland
Bud trees responded badly to conditions that produced little or no injury to Cortland/P1 trunks, indicating that Bud bark and cambium were more cold tender. Cropping and tree vigor in the previous year, based upon my recollection, would not have been a factor. Perhaps the difference is in the number of chilling hours needed to bring the trees out of physiological rest. Might the Bud trees have a significantly shorter chilling requirement than Cortland/P1? My maximum-minimum temperature records indicate that there were about 546 hours below 45F in November; 720 hours in December, and 48 hours in January prior to the first cold night, January3. If that was sufficient to break rest in the Bud trees, the 4 days with maximums of 50-62F in the first 11 days of January would probably have stimulated some growth activity in those Bud trees. I think it unlikely that injury was initiated by the early January cold, because at that time none of the trees had been pruned. In other years, in other block, I have found that only dormant-pruned trees have shown winter trunk injury. The block containing Bud trees was pruned just prior to the February 11 cold. It seems reasonable to me that injury was inflicted on February 11 (4F) or February 29 (5F), or both.
David Kollas, Tolland,Connecticut, February 4, 2009
