- 6 



where plant injury occurs, 

 jury increased over a 5-day 

 24°F to 12°F. Although the 

 the freezing period, it was 

 occupies in crowns of field 



Under laboratory conditions, crown in- 

 period within the temperature range of 

 amount of injury increased throughout 

 most rapid during the first day. Therm- 

 plants here have recorded temperatures 

 of 20"F or lower for periods longer than 5 days. 



Repeated freezing and thawing under controlled conditions sig- 

 nificantly increased crown injury compared to plants frozen only 

 once. The more often they were frozen, the more injury resulted. 

 Increased injury of this nature on field plants may be more of a 

 problem in early spring than during the winter. Crown temperature 

 recordings have indicated that during the winter, plants covered 

 with mulch or snow seldom thaw out. But in the early spring, crowns 

 frequently freeze and thaw, especially on unmulched plants. 



Each spring injury may be more of a problem than is commonly 

 recognized. Hardened strawberry plants placed under ideal grow- 

 ing conditions began to lose their hardiness within two days. Af- 

 ter a week, they had lost an appreciable amount of resistance. If 

 this occurs under field conditions, the plants would be subject to 

 injury during early spring at temperatures that would be of little 

 concern in the winter. 



Mulching plants in the fall of the year is presently the only 

 practical means of reducing the chances of low temperature injury. 

 A straw mulch minimizes the adverse effects of many of the above 

 factors. Continuous snow cover offers by far the best protection; 

 unfortunately , i t cannot be depended on. Six inches of snow will 

 keep crown temperatures above the point of injury when air temper- 

 atures drop to -20 F. Snow fences or other means of accumulating 

 snow over the plants may help reduce injury, especially when low 

 temperatures follow a mid-winter thaw before additional snow cover 

 occurs . 



Once the tissues are injured, the growing conditions the fol- 

 lowing season will influence the vigor, yield, and even survival 

 of the plants. With a specific amount of injury, plants growing 

 under optimum conditions will have a better chance than under ad- 

 verse conditions. 



*************** 



PUBLICATION AVAILABLE : Available from New York State Agricultural 

 Experiment Station, Geneva, New York, is Bulletin No. 817, entitled 

 "Propagating Fruit Trees in New York." In this publication, the 

 following topics are discussed: (1) appropriate rootstocks for 

 use with various species and varieties of deciduous fruit trees; 

 (2) methods for growing rootstocks from seeds; (3) propagation of 

 clonal rootstocks by means of stooling beds and cuttings; and (4) 

 budding and grafting techniques. 



