1919] Coit-Hodgson: Abnormal Shedding of Washington Navel Orange 331 



their improved health brought about by better soil moisture and humus 

 conditions as well as improved temperature conditions. It has not yet 

 been satisfactorily shown that the mulched-basin system alone will 

 reduce the amount of drop on healthy trees, although in the light of 

 the discussion above we believe it probable. 



The determination of the specific factor, if it be a single factor, 

 which produces the abnormal water relations established, is yet to be 

 made. It is hoped that investigations planned for the coming season 

 may aid in solving this question. The orchard management practices 

 described above which result in heavier crops, unfortunately for in- 

 vestigational purposes, involve the modification of both the above- 

 ground and under-ground environmental complex. 



The fact that by proper means man is able to change the climatic 

 conditions from those obtaining at Tucson, Arizona, to those at Miami, 

 Florida, within the space of a half mile, augurs well for the successful 

 control of the June drop. Measures of an anticipatory nature lie in 

 the proper selection of the site before planting. The exposure to pre- 

 vailing winds, the nearness to large irrigated tracts, the possibility of 

 planting windbreaks; all these should be considered in the selection 

 of a site for a Navel orange grove. Growers should accustom them- 

 selves to thinking of climate not in terms of great valleys and states 

 but in strictly local terms. As has been pointed out above, the judicious 

 selection of the site, coupled with proper methods of orchard practice, 

 make it possible to secure marked modifications in our arid climate. 

 The question of the advisability of the measures suggested is purely 

 one of farm economics and does not lie within the province of this 

 paper. 



In view of the relatively small amount of shedding which is con- 

 nected with the Alternaria fungus alone and because of the peculiar 

 manner of infection the authors are led to believe that spraying with 

 fungicides for the June drop will hardly pay for the materials and 

 labor involved. 



Another promising line of investigation looking toward control of 

 the June drop lies in the selection and propagation of dry heat resist- 

 ant strains of the Washington Navel variety. This variety, it is well 

 known, is constantly throwing off bud sports or mutations and it is 

 entirely possible that mutations may arise which are less sensitive to 

 abscission stimuli, but at the same time satisfactory otherwise. Every 

 grower should be on the lookout for such strains. 



