. Bulletin of the Department of Agriculture. Agriculture; 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 tul
. Bulletin of the Department of Agriculture. Agriculture; 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
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