Studies on the Fire-Blight Organism, Bacillus amylovorus 39 



A similar experiment was conducted at Rochester, using the varieties 

 Rhode Island Greening and Tompkins King. This work was started 

 on May 21, just as the blossoms were opening. Inoculations above the 

 bags were made on May 22. The results are shown in table 7. 



These tests were repeated in 1926 with the same varieties in the same 

 orchards, and in each case the bags were tied over the branches just 

 before the blossoms opened. In addition to the foregoing, thirteen bags 

 were tied on three Wagener apple trees at Ithaca which had blighted 

 severely in 1925. No inoculations were made above these bags, and, 

 as later examination revealed, they were unnecessary, for the majority 

 of the unbagged blossoms, probably 80 per cent, blighted. No blight 

 cankers could be found on the trees at the time when the blossoms were 

 bagged. No blighted blossoms developed in any of the bags on these 

 trees (table 7). 



In addition to the foregoing, the writer made observations on apple 

 blossoms inclosed in cheesecloth bags by the Department of Pomology 

 ;i1 Cornell University for pollination studies. The varieties used were 

 Rhode Island Greening and Twenty Ounce. About two thousand blos- 

 soms were observed in both 1925 and 1926, and, although blossom 

 blight was severe on unprotected blossoms, the blossoms within the bags 

 showed but one cluster blighted. This was on a Twenty Ounce tree 

 and at the extreme end of a branch with no other branches above it. 

 The writer is unable to explain how this cluster became inoculated, 

 unless an insect inoculated it through the bag. No holes could be 

 found in the bag. 



From these data it appears that, under the conditions of the experi- 

 ments, rain at blossoming time did not play a very important part in 

 the dissemination of B. amylovorus. It is possible, and highly probable, 

 thai where -oozing cankers are located above the blossoms, rain may 

 act as a disseminator of fire blight. Instances where this appeared to 

 have happened have been observed, but they could not be verified as 

 hordes of insects had visited the blossoms. The observations of tin 1 

 writer indicate that, as a rule, blossoms do not become sufficiently 

 charged with bacteria to act as centers of inoculation for rain dis- 

 semination until after the petals have fallen. 



It may be argued that the cheesecloth bags prevented, the rain from 

 inoculating the inclosed blossoms. This does not appear probable, as 

 the cloth whs of a coarse weave. Since fire blighl was severe at Ithaca 

 in both 1925 and 1926, and at Rochester in 1926, disseminators other 

 than meteoric water must have caused the spread. 



Field experience in southern Ohio in 1928 adds further evidence of 

 transmission of the fire-blight organism by insects. An isolated apple 

 grower had severe blossom blight on Jonathan and Grimes apple trees 



