LIBRARY 



NEW YOt<K 

 BOTANICAL 



JOMAL OF AOtlQllTIML RESEARCH 



Vol. XIX Washington, D. C, May 15, 1920 No. 4 



HALO-BLIGHT OF OATS ' 



By Charlotte; Elliott 



Scientific Assistant, Laboratory of Plant Pathology, Bureau of Plant Indxistry, 

 United States Department of Agriculture 



INTRODUCTION 



The present paper is a description and discussion of a bacterial disease 

 of oats which has been the subject of investigation by the writer for the 

 past three years. This "halo-bhght" is a disease which occurs to at 

 least some extent each year throughout the oat-growing sections of the 

 central and eastern States and becomes of economic importance during 

 certain seasons when weather conditions are particularly favorable to 

 its development. 



During the season of 191 8 field observations and specimens of 

 diseased plants from widely separated sections of Wisconsin showed 

 that this disease occurred in practically all the oat fields of the State 

 and was responsible for the abnormal condition prevalent in the early 

 part of that season. 



DESCRIPTION OF HALO-BLIGHT LESIONS 



The halo-blight is most conspicuous on the leaves (PI. C; 26), although 

 it may occur on leaf sheaths and glumes (PI. 29). Typical well-developed 

 lesions of the disease are oval chlorotic spots /^ to 2 cm. or more 

 in diameter about points of infection which consist of gray-brown col- 

 lapsed tissue measuring from i to several millimeters in length. The 

 halolike border is at first only shghtly lighter green than the surrounding 

 tissue, but as it becomes older it loses more of its green color and forms 

 oval yellow halos about the central infection areas. 



Lesions are first visible as light green oval spots 4 to 5 mm. in diameter 



with central sunken points of infection at first evident only on one side 



^ , of the leaf. This center of infection increases slowly in size, penetrates 



bS — — 



^~ ' The greater part of this work was carried on at the University of Wisconsin during 1917 and 1918 



f^ under the direction of Prof. L. R. Jones and was continued in the Pathological Laboratory of the United 



■ States Department of Agriculture during 191S and 1819 under the direction of Dr. Erwin F. Smith. The 



writer also wishes to acknowledge the courtesy of the Boston Branch of the Association of Collegiate 



2r! Alumnae whose research fellowship she held during the coUege year of 1917-18. 



=D ^ __ 



^^ Journal of Agricultural Research, Vol. XIX, No. 4 



Washington, D. C. May 15, 1930 



uc Key No. G-igx 



(139) 



