UNITED STATES DEPARTMENT OF AGRICULTURE 
&J?'<$Wu 
I BULLETIN No. 842 
Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 
Washington, D. C. 
PROFESSIONAL PAPER 
September 7, 1920 
THE NEMATODE DISEASE OF WHEAT CAUSED BY 
TYLENCHUS TRITICI. 
By L. P. Byaes, formerly Pathologist, Office of Cotton, Truck, and Forage Crop 
Disease Investigations, in cooperation with the Office of Cereal Investigations. 
CONTENTS. 
Occurrence of the disease 
History 
Distribution 
Economic importance 
Description of the disease 
Differences between this disease and 
tulip-root 
Origin and description of the galls 
Cause of the disease 
Page. 
1 
2 
4 
Effect of high temperatures on the 
larvae 
Effect of chemicals on the larvae 
Overwintering of the parasites — 
Host plants 
Methods of spreading the parasites 
Methods of control 
Summary 
Literature cited 
Page. 
19 
24 
27 
28 
30 
32 
35 
37 
OCCURRENCE OF THE DISEASE. 
A disease of wheat caused by the nematode Tylenchus tritici 
(Steinbuch) Bastian has been known for many years in certain 
European countries, where it causes considerable damage. The dis- 
ease manifests itself most strikingly in the wheat heads. Here 
rather small dark-colored galls of the same general shape as wheat 
kernels are formed in place of normal grains. It is also known to 
affect other aerial parts of the wheat plant, but does not attack the 
roots. In thrashing, many of the nematode galls thrash out with the 
wheat. Examinations by the writer of numerous samples of wheat 
collected during the winter of 1917-18 by the Office of Grain Stand- 
ardization, of the Bureau of Markets, at mills and other places, re- 
vealed the presence of many of these galls and showed for the first 
time that the disease occurs to a serious extent in certain localities 
in the United States, particularly in Virginia. Subsequent observa- 
tions in the field have shown that the pest in some instances destroys 
more than 10 per cent of the growing wheat. It therefore seems de- 
151572°— 20 1 
