To know if winter twig die-back of double grafted apple nursery trees, when fall-planted, is caused by low temperature or Winter desication, both percent twig die-back and/or cold hardiness of the apple twigs were measured on four different collection dates during the period of Jan. 8 to April 22, 1976.
The results were shown as follows:
1. Any fall planting on six different times with about 10 das interval during Sept. 20 to Nov. 20, 1975 did not significantly affect the cold hardiness of the apple nursery trees at three collection dales of Jan. 8, Feb. 23, and Mar. 15, 1976. Neither grafting periods of April 5, July 5, and August 5, nor twig positions of tip and base affected the cold hardiness.
2. The percent twig die-back decreased as nursery trees were planted in later Season to Winter. The nursery trees planted on November 10, 1975 showed the lowest damage. The nursery trees planted on November 20 showed more damage than the November 10 one, but less than the others.
3. Any untransplanted nursery trees were not damaged, very little, if any, and was not serious for its survival. The nursery trees planted on October 10 showed difference in twig die-back among their grafting dates.
The ones grafted on April 5, 1975 had less percent twig die-back than the grafted on July 5 which showed about same final damage, but earlier damage development.
4. Most twig die-back began at the tip of the twigs and proceeded downward up to graft union of the interstock all of which was not damaged.
The above results indicated that the twig die-back of fall-planted apple nursery trees was caused by winter desication, but not by the low temperature.
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