UNITED STATES DEPARTMENT OF AGRICULTURE 



1 BULLETIN No. 842 



j\Jr < &-ru 



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 ivith 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 

 6 

 6 



9 

 10 



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 40 per cent of the growing wheat. It therefore seems de- 



151572°— 20 1 



