junei2, i9i6 Bacterial Wilt of Cucurbits 433 



Two more tests (Jan. 19, 191 6) were made with Baltimore Nutmeg 

 cantaloupes planted November 13, 191 5, using a bacterial strain of low 

 virulence (strain R311) and one of high virulence (strain R304). The 

 cultures of these two strains used for inoculation were beef-agar slants 

 10 days old. With the former strain 10 unsprayed and 9 sprayed plants 

 were inoculated, and these gave, respectively, 40 and 11 per cent of 

 infection. With the highly virulent strain 16 unsprayed and 17 sprayed 

 plants were inoculated. These gave, respectively, 94 and 24 per cent 

 infection. 



Remarks : It will be seen that in all cases the presence of Bordeaux 

 mixture on the leaves greatly reduced infection, and an average of the 

 six trials gives 80.6 per cent of infection in the unsprayed against 26 per 

 cent of infection in the sprayed plants. These results can scarcely be 

 considered as accidental, and they strongly confirm field observations 

 regarding the bactericidal effect of Bordeaux mixture. Furthermore, the 

 natural mode of inoculation is considered identical with the method used 

 in these tests, for in the one case the organism is pricked into the leaf 

 tissues by the mouth parts of the cucumber beetle and in the other case 

 by the inoculating needle. 



Wet and Dry Inoculations 



On January 8, 1915, an experiment w^as conducted to determine the 

 effect of wet and dry inoculations into sprayed and unsprayed plants. 

 In this test 68 cucumber plants were used. The inoculations were all 

 made in a uniform manner by needle punctures into the two youngest, 

 fully opened leaves of each plant. Of these plants 34 were sprayed with 

 Bordeaux mixture and 17 were inoculated before the Bordeaux mixture 

 had dried. The remaining 17 were inoculated about 2 hours later when 

 the Bordeaux mixture was thoroughly dry. At the same time 34 

 unsprayed plants were inoculated, 17 while dry and 17 immediately after 

 sprinkling with tap water. All of the plants were shaded from the sun 

 until the following day. At the end of 19 days after inoculation 95 per 

 cent of the unsprayed plants inoculated when wet had contracted the 

 wilt and 88 per cent of those inoculated when dry. In the sprayed 

 plants there was 33 per cent of infection among those inoculated before 

 drying and 36 per cent among those inoculated after drying. 



As will be seen, the percentage relations between infection in wet and 

 dry leaves vary inversely in the sprayed and unsprayed plants. The 

 difference is small, but it occurs in the direction to be expected from 

 known facts concerning conditions favorable to infection. In the 

 absence of bactericidal substances a moist leaf surface presents a better 

 environment for infection by the bacteria; but when a bactericide is 

 present which is effective in solution the maximum effect occurs in the 

 presence of water. This is exactly the result obtained in the experiment 

 under discussion. 



