- 13 



Warm weather in February, March, and April produced an earlier bloom 

 and lowered yield. This was not due to a greater frequency of frost damage, 

 as wlrm periods tended to continue on into summer. The authors suggested 

 that the early bloom produced by this weather either resulted in "poorer 

 quality of flowers" or else was associated with lessened insect activity. 

 In either case, poorer fruit set would result. Relatively high tempera- 

 tures immediately after full bloom increased yield. The authors related 

 this to known effects of temperatures on pollen tube growth, suggesting that 

 rapid pollen tube growth increased fertilization of seeds and produced 

 higher yields (fruit size tends to increase with seed number). Relatively 

 cool weather in June related to reduc ed yields. The authors suggested that 

 this was due to slower growth during This time of cell division and/or to 

 poorer fruit retention during June drop. 



Together, these 4 factors (technological improvement and temperatures 

 during these 3 key times) accounted for 80% of the variation in estimated 

 yield over this time period. Using this information, "expected yield" was 

 calculated for each of these years and the values were very close to actual 

 estimated yields in all years except those in which some frost damage 

 occurred. Thus, it appears that the ideal weather for high yields in 

 England would be to have (a) a relatively late Spring, (b) relatively high 

 temperatures immediately after full bloom, and (c) relatively high tempera- 

 tures again during late June. 



Dr. Alan Lakso of the New York Agricultural Experiment Station, Geneva, 

 NY, has examined the effects of temperature from February 1 to April 15 on 

 New York apple yields over a 15-year period ( The Great Lakes Fruit Grower s 

 News , April, 1984). He found results similar to those of Jackson and Hamer 

 in England . 



Using the mean maximum temperature for February 1 to April 15, he found 

 that higher temperatures lowered yield. The relationship of weather to 

 yield was further improved by considering the mean temperature during the 

 two weeks after petal fall, in which higher temperatures increased yield. 

 Using just the temperatures for these two periods of the year, 80% of the 

 annual variation in apple yield was accounted for. 



Information such as this may allow early predictions of yields and aid 

 growers in making management decisions about their crops. 



***** 



POMOLOGICAL PARAGRAPH 



Rootstock mixtures . In Massachusetts Agricultural Experiment Station 

 Bullftin No. 418 published in 1944, J.K. Shaw stated "we are inclined to 

 favor Ml, M2, M4 and M7 as the semi-dwarfing rootstocks most likely to prove 

 valuable and it wou 1 d simpl ify matters if this list could be shortened ." In 

 the 1930s and 1940s, the Mailing series were the only available rootstocks. 

 Certainly, the chance of mixtures is much greater today because of the 

 numerous rootstock introductions since the 1940s. 



