- 4 - 



the rest period ended early In January. The reason for this is that three or 

 four days of mild temperature while the buds are in rest result in little if any 

 loss in hardiness, but similar conditions after the rest period can cause appreci- 

 able loss in hardiness. Buds usually regained hardiness with succeeding periods 

 of cold weather. This loss and gain of hardiness occurred periodically until the 

 buds were advanced to the pink stage in the spring. In spite of the frequent 

 periods when a warming trend during the winter caused loss in hardiness, a return 

 to seasonal temperatures prevented extensive bud activity. Once the hardiness 

 index for Halehaven dropped below -4*^. in late fall, it did not rise above this 

 point until there was visible swelling of the buds in the early spring. 



"This fluctuation in hardiness while the buds were still dormant was of such 

 magnitude that maximum hardiness developed during a prolonged cold period in 

 January 1948, and 15 per cent of the Halehaven buds survived -19°F. Ti7o years 

 later when above-normal temperatures prevailed during January, only moderate 

 hardiness was attained and a temperature of -8°F. in February killed about the 

 same percentage of buds on these same trees. 



"The effect of several orchard practices on bud hardiness was investigated. 

 A reduction in fruit set by the use of chemical thinning sprays increased bud 

 hardiness the follovfing winter. 



"Moderate differences in the level of nitrogen fertilization had little 

 effect on peach bud hardiness. The effect of cultivation was compared with dif- 

 ferent cover-cropping practices and likev^ise no significant effects on bud 

 hardiness were detected within the levels of tree vigor obtained in these tests. 



"Studies on cold hardiness of the woody tissues indicated much slower 

 development of hardiness in the wood than in the flo^7er buds. It was usually not 

 until early December that the twigs became more resistant to Imi temperature in- 

 jury than the f.la\iev buds, but from that time on, the bark, cambium, and sapwood 

 of twigs and miain branches were generally more hardy than flo':;er buds. 



"Chemical thinning was found to promote wood hardiness during the subsequent 

 winter. A nitrogen status high enough to cause excessive vegetative growth in a 

 tree also hindered development of hardiness, but of wood more than bud hardiness. 



"Early winter pruning had a marked effect on susceptibility to cold injury 

 in both twigs and main branches." 



---William J. Lord 



Nutritional Needs for IK^arf Apple Trees 



The Di7arf Fruit Tree Association News Letter , April, 1961, contained the 

 follox/ing paper presented at the fourth annual meeting of the association by 

 Dr. A. L. Kenworthy, Department of Horticulture, Michigan State University. 



"We have often heard and read reports that rootstocks do affect the nutri- 

 tional requirements of fruit trees. It is not difficult for us to accept the 

 fact that different rootstocks will absorb different quantities of the various 

 nutrients. For the past six years we have been studying these effects. The 

 facts speak for themselves. Not only rootstocks but interstems affect nutrient 



