ANNUAL REPORT, 1947-48 67 



earlier thinning can be done the greater are the chances of obtaining desirable 

 commercial size with the least reduction in jneld and of making alternate-bearing 

 varieties bear more uniform annual crops. 



The Nature of Winter Hardiness in the Raspberry. (J. S. Bailey and A. P. 

 French.) By bringing raspberry canes into the greenhouse during the winter 

 and observing the rate at which they started into growth it was found that the 

 raspberry had a very short rest period and that there were varietal differences. 

 This suggested that there might be a relationship between the length and in- 

 tensity of winter rest and cold resistance. 



To test this possibility canes of six varieties were brought into the greenhouse 

 at regular intervals during three winters. The varieties Chief and Latham were 

 selected as cold-resistant varieties, Marcy and Washington as tender varieties, 

 and Milton and Taylor as intermediate in cold resistance. It was found that 

 the cold resistant varieties go into a deeper rest and come out more slowly than 

 the tender varieties. A report on this work will appear in the Proceedings of the 

 American Society for Horticultural Science. 



The raspberry planting used in this work was set in the spring of 1942. The 

 planting was divided in half. One half was given a heavy mulch of hay or straw, 

 whichever was available, and additional mulch added annually. The other 

 half is cultivated with a cover crop sown in midsummer. These plots were sub- 

 divided, making a total of four plots. One mulched plot receives no additional 

 nitrogen and the other NaNOj annually at the rate of 225 pounds per acre. 

 One of the cultivated plots receives NaNOs annually at the rate of 225 pounds 

 per acre, the other at the rate of 450 pounds. Until the winter of 1947-48 there 

 was no indication of diflferential winter injury between the mulched and cultivated 

 plots. During the winter of 1947-48 there was definitely more winter injury on 

 the mulcheH plot. 



Since the type of mulch used results in high soil nitrates, it was thought that 

 nitrogen supply might be a factor. However, when the data were broken down 

 according to the four plots varying in nitrate application, there was no relation 

 between winter injury and the amount of NaNOa applied. 



During the winter of 1947-48, freezing tests were made to determine the rate 

 of hardening of raspberries. The only low-temperature rooms available were in 

 a large room held at 0° F. for storing frozen foods and in a sharp freeze room 

 ordinarily held at —15° F. Canes of the Chief and Latham varieties were used 

 to represent cold-resistant varieties and canes of Marcy and Washington to 

 represent varieties lacking cold resistance. On November 18 and December 1 

 canes of all four varieties were severely injured by 24 hours' exposure to 0° F. On 

 January 13, following a period of several days with temperature near 32° F., 

 sudden exposure to 0°F. resulted in less injury than in previous tests. By shut- 

 ting off the ammonia and opening the door, the temperature in the sharp-freeze 

 room was raised to 30° F. Lots of canes were placed in the room and the door 

 shut. The temperature dropped to +9° F. in one hour and fifteen minutes and 

 to -|-7° F. in 24 hours. This treatment resulted in slightly less injury than 

 sudden exposure to 0° F. 



Another lot of canes was brought in for test February 19. At this time there 

 was evidence that injury had occurred outside. Exposure to 0° F. caused some 

 injury, but the difference between treated and check was not great because of 

 the injury which occurred before the canes were brought in. Exposure to 0° F. 

 caused less injury than earlier in the season. The hardy varieties. Chief and 

 Latham, withstood the temperature drop better than the tender varieties, Marcy 

 and Washington, 



