RELATION OF WEATHER TO FRUITFULNESS IN 

 THE PLUM* 



By M. J. DORSEY 

 Head of Section of Fruit Breeding, Agricultural Experiment Station of the University 



of Minnesota 



Under suitable growing conditions the plum tree is remarkable for the 

 uniformity with which it annually produces a crop of flower buds. 

 Bearing a full crop of flower buds annually, however, does not insure a 

 full crop of fruit annually; therefore, it is evident that a considerable 

 number of flowers fail to set fruit. ^ From the standpoint of fruit pro- 

 duction, thinning, up to three-fourths of the bloom, is actually beneficial, 

 but beyond this the margin is approached where the thinning process 

 reduces the yield and there is economic loss. The status of setting in 

 controlled crosses known to be fertile under tents was similar to that 

 in the orchard generally. This general condition led to an attempt to 

 isolate those factors of the weather influencing the setting of fruit which 

 result in such great differences as a complete crop failure one year 

 and an overproduction of fruit another. 



The elements of what is commonly known as "weather" which have 

 a bearing upon pollination and fertilization are wind, temperature, 

 sunshine, and rain. The combinations of these most favorable to the 

 setting of fruit are sunshine, a relatively high temperature, slight or no 

 wind, and an absence of rain. It is apparent that certain weather con- 

 ditions, good and bad, go together, but temperature and rain are undoubt- 

 edly the most important elements considered from the standpoint of 

 the setting of fruit and will be given greatest emphasis. 



The following statements may be regarded as fairly typical of the 

 conception of the influence of unfavorable conditions at bloom. Cold 

 weather, rain, poor locality, and severe cold winter weather are men- 

 tioned by Goff (4) ^ as inhibiting fruitfulness. Bad weather at flowering 

 time has an "injurious influence on fruitage" by keeping away insect 

 visitors and affecting the fecundation of the flowers (13). Damage to 

 flowers by wind, hail, rain, insects, and fungi are commonly mentioned. 

 Lord (11) states that all varieties when in bloom are extremely sensitive 

 to cold or wet weather. Heideman (9) notes that ample cross-fertiliza- 



1 Published, with the approval of the Director, as Paper 162 of the Journal Series of the Minnesota Agri- 

 cultural Experiment Station. 



2 "Setting of fruit" is a term in common use among fruit growers. In general, it is used in referring 

 to the number of pistils which are swelling or "setting" six weeks or so after bloom. A distinction is 

 made in common usage between the percentage of fruit to set and the percentage of a crop, in that the * 

 latter is used in speaking of mature fruit. 



'Reference is made by number (italic) to "Literature cited," p. 125-126. 



Journal of Agricultural Research, Vol. XVII, No. 3- 



Washington, D. C, June 16, 1919. 



ru Key No. Minn. — 38. 



(103) 



