Mar. 22, 1924 
Nematode Disease Caused by Tylenchus tritici 
95i 
The larvae are quite transparent by this time, having used up much of 
the reserve food material in their bodies, but they are still alive and 
active after having been in a free-living state for 9 or 10 months. It 
has been found, however, that they do not survive in the soil long enough 
to infect a subsequent wheat crop after a nonsusceptible crop has occu¬ 
pied the land for a year. Neither will land infested at harvest time 
produce pronounced infection in spring wheat sown the following April. 
LOW TEMPERATURE 
Investigators differ as to the minimum temperature that can be 
endured by the larvae. Marcinowski (17) states that larvae between 
the leaf sheaths of plants are killed at a temperature of —14 0 C. Davaine 
(9) claims that larvae can endure a temperature of — 20°, and Penne- 
tier ( 20 ) also states that he exposed larvae to a temperature of — 20° for 
five hours or more without killing them. Neither states whether the 
larvae were within the galls or in a free-living condition. 
The writer exposed soaked galls to a temperature of — 40° C. for five 
minutes. The galls were then opened in water and the larvae were 
observed to move actively within a few hours. A section of a rye¬ 
seedling stem containing larvae was similarly exposed to — 40° for 
five minutes and then placed in tap water. The larvae remained straight 
and at no time during the 40 hours following did they show any indica¬ 
tion of life, while larvae from another section of the same stem not 
exposed to the cold continued active movement. This seems to show 
that larvae taken directly from the galls can endure cold, as well as 
desiccation, to a greater degree than larvae that have been in a free- 
living state for some time. This undoubtedly explains the difference in 
the findings of Marcinowski (if) and those of Davaine (9) and Penne- 
tier (20). 
HIGH TEMPERATURE 
Byars*. (6) experiments on the effects of high temperature on the 
larvae both within and outside the galls showed that in previously soaked 
galls larvae are killed by immersion in water at 50, 52, 54, and 56° C. 
for 30, 20, 10, and 5 minutes, respectively. In galls not previously 
soaked in water a longer time is required. Free larvae placed in water 
at the above temperatures succumbed in half the time required to kill 
those inside the soaked galls. It happens that the same temperature 
fatal to nematodes in the galls is effective in controlling loose smut of 
wheat, so that if seed wheat in the infested region is treated for the 
latter disease the nematodes, if present, also are killed. 
chemicals 
It has been found ,that any chemical able to penetrate the thick wall of 
the gall and kill the larvae inside will also kill the embryo of seed grain. 
Therefore, any attempt to control the nematode disease by treating the 
seed with chemical disinfectants is impracticable. Even when outside 
of the gall, the tough body wall of the nematodes makes them extremely 
resistant to the toxic action of chemicals. 
Pennetier (20) states that the free larvae can endure 0.5 per cent 
sulphuric acid for two hours, 25 per cent alcohol for six hours, and glyc¬ 
erin for one month. Byars (6) found that nearly five hours in for- 
