UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 519 



little subject to the scab fungus and ordinarily its setting of fruit will not 

 be materially reduced by it, though a Winesap crop in the same orchard 

 may be practically ruined by its work upon the blossoms. In California 

 brown rot is a serious disease on the blossoms of the apricot only in 

 "regions exposed to ocean influences and does not develop except in 

 times of unusually moist weather.""^ 



Fortunately most of the fungous and bacterial diseases that attack 

 the blossoms of fruit trees can be controlled by spraying or other preven- 

 tive measures; consequently losses due to these factors are avoidable in 

 many cases. 



Spraying Trees When in Bloom. — Though spraying trees with the 

 proper materials may be effective in preventing the attacks of certain 

 diseases that otherwise would seriously reduce the set of fruit, it is not 

 necessary or desirable to spray during blossoming. Spray applications 

 at that time are seldom recommended and are generally regarded as 

 undesirable. They may reduce the set of fruit either directly through 

 injuring the pollen or stigma or indirectly through interfering with the 

 work of bees and other pollen-carrying insects. 



Beach* made a number of laboratory cultures of pollen grains in 

 media to which varying amounts of Bordeaux mixture alone and Bor- 

 deaux mixture with an arsenical poison had been added. He found 

 that 200 parts of Bordeaux mixture to 10,000 parts of his culture media 

 practically prevented the germination of pollen and that much smaller 

 amounts had a distinct inhibiting influence. On the other hand in one 

 experiment sprajdng apricots when in bloom with the regular summer 

 strength of the lime-sulfur mixture and with a weak Bordeaux mixture 

 caused no injury to the flowers and no interference with fruit setting. ^^ 

 This suggests at least that in actual field practice no great injury in 

 fruit setting is likely to result from the use of fungicides alone when trees 

 are in bloom. 



Apparently the indirect effects on fruit setting of spraying with 

 arsenical poisons when trees are in bloom are much more serious. It 

 has been shown that a very small amount of arsenic — less than 0.0000005 

 gram of arsenious trioxide — is a fatal dose for a bee and most bees die 

 within a few hours after being poisoned. ^"^ Bees work as freely upon 

 sprayed as upon adjacent unsprayed trees. Price ^"^ found that the mor- 

 tahty of bees in a check cage was only 19 per cent., as compared with 69 

 per cent, in a lime-sulfur-arsenate of lead sprayed cage and as compared 

 with 49 per cent, in a sulfur-arsenate of lead dusted cage. 



The suggestion is made that if it has been impossible to spray before 

 blossoming for the control of fungi which interfere with fruit setting and 

 such fungi are known to be present to a serious extent, spraying may con- 

 tinue into, or even through, the blossoming season, but a fungicide alone 

 should be used at that time. 



