246 ILLINOIS STATE ACADEMY OF SCIENCE 



A SUMMARY OF THE PLANT DISEASE SITUA- 

 TION IN 1922 WITH RESPECT TO THE 

 CROPS OF ILLINOIS 



Leo R. Tehon, Botanist, State Natural History Sur- 

 vey Division, Urbana 



Plant diseases are factors of extreme importance in 

 crop production. Each year crop reductions are attribu- 

 ted to them which, if translated into terms of dollars, 

 would appear amazingly large. All are not equally se- 

 vere every year, but vary according to climatological 

 conditions and the abundance of infectious materials. 

 Observations of plant disease from year to year are 

 useful in that they tend to indicate what may be ex- 

 pected under specific conditions subsequently, and their 

 publication is justified as forming a concise and perma- 

 nent record for future reference. 



A year ago the writer prepared a statement of the 

 purposes of a plant disease survey of the state, con- 

 ducted as a part of the activities of the State Natural 

 History Survey Division, and included a number of ob- 

 servations on plant disease conditions during 1921. 



This paper proposes to summarize briefly the disease 

 situation with respect to the crops of the state for the 

 year 1922. In securing the material upon which the sum- 

 mary is based a force of four men was placed in the field 

 from about the first of June until the last day of August. 

 Their reports and observations are substantiated by rep- 

 resentative specimens of disease deposited in the Survey 

 Herbarium. A considerable amount of additional mater- 

 ial has been obtained from other sources. 



WEATHER CONDITIONS 



The abundance and severity of plant infection is always 

 influenced extensively by climatological conditions. As 

 a whole these conditions were not conducive to the de- 

 velopment of severe infections during 1922. The year 

 was the warmest, with the exception of 1921, in the cli- 

 matological history of Illinois. The precipitation was 

 below normal throughout the state, while during the crop 

 growing period the precipitation was 15 per cent less 

 than normal for that period. 



