NEMATODE DISEASE OF WHEAT. 21 



By increasing the temperature of the water to 52° C, all larvae be- 

 come motionless and lifeless after an exposure lasting 20 minutes. 

 Exposures for a shorter time than this considerably reduced but 

 did not entirely stop larval activity. In water at 54° C. the larvae 

 were practically all killed in 10 minutes, although there were six 

 larvae from one gall, or 0.02 per cent of the series, which at the end 

 of this time showed faint signs of life. Likewise, when treated' at 

 the same temperature for 15 minutes, 0.01 per cent, or three larvae, 

 were found sluggishly moving. In both cases the fractional per- 

 centages of nematodes not killed are small enough to come within 

 the expected limits of error, and in addition the faintly moving 

 larvae appeared so weakened as never to be able to parasitize the 

 host. Thus, at least for all practicable purposes, these two treat- 

 ments seem absolutely effective. No living larvae were found in 

 galls immersed longer than 15 minutes in water at 54° C, and the 

 same was true if they were exposed to the liquid at 56°, 58°, and 

 C0° C, respectively, for 5 minutes or more. 



In the check experiments, 95 per cent of the unheated larvae in 

 the soaked and dry galls remained alive throughout the investiga- 

 tions. 



It is both interesting and important to note that the hot-water 

 treatments found effective for the nematode should so closely corre- 

 spond to those which have been used successfully in controlling the 

 loose smut of wheat caused by Ustilago tritici. Humphrey and Potter 

 (17) recommend treating water-soaked wheat for 10 to 15 minutes 

 in water heated to a temperature ranging from 52° to 57° C. (125° 

 to 135° F.) to control this smut. Because of this fact, a single 

 operation should suffice for both the nematode disease and the smut. 



DRY GALLS. 



Larvae within dry unsoaked galls are much less affected by a 

 given hot- water treatment than those contained in galls previously 

 moistened throughout. No doubt this is due to the longer time re- 

 quired to raise the internal temperature of the dry gall to the thermal 

 death point of the nematode. As shown in Table II, 29 per cent of 

 the larvae survived a hot-water treatment of 50° C. for 30 minutes, 

 while 36, 24, and 55 per cent lived after immersions in water at 52° 

 C. for 20 minutes, 54° for 10 minutes, and 56° for 5 minutes, respec- 

 tively, all of which are treatments to which the larvae in soaked 

 galls succumbed. Only by increasing the time of exposure beyond 

 that specified were the various temperatures entirely effective in 

 killing the nematodes. 



The figures obtained by the writer on the hot-water treatments 

 differ materially from those of Davaine (11) and Marcinowski (22), 

 who state that larvae in galls are not killed by an immersion for 10 



