88 ILLINOIS STATE ACADEMY OF SCIENCE 



SOME OUTSTANDING FEATURES OF THE 



PLANT DISEASE SITUATION IN ILLINOIS 



DURING 1923 



L. R. Tehon, State Natural History Survey, Urbana 



The progress of plant disease infection, especially of 

 crop plants, throughout the state, was kept under ob- 

 servation during the season of 1923 by the Natural His- 

 tory Survey's botanists. Their observations are repro- 

 duced in condensed form in this paper as a continuation 

 of the papers presented at the two previous meetings of 

 the Academy. 



During the 1923 season plant diseases appeared in Illi- 

 nois in their usual abundance and those attacking crop 

 plants w T ere responsible for large crop losses. The un> 

 usual weather conditions of the season favored the de- 

 velopment of certain diseases, not usually very serious 

 in our state, to the extent that they took on the appear- 

 ance of severe epidemics. 



WEATHER SUMMARY 



While the mean temperature for the year 1923 was 1° 

 above normal for the state, seasonal variations in tem- 

 perature and precipitation in various parts of the state 

 interfered with the usual routine of crop production. 

 The snowfall was deficient in all parts of the state during 

 January and February, leaving over-wintering crops ex- 

 posed to the low temperatures recorded in Februar} 7 . 

 Four months beginning with February had mean tem- 

 peratures below normal and resulted in a backward 

 spring which delayed the growth of winter wheat and the 

 planting of corn. Precipitation was below normal north 

 and west of the Illinois river, and generally above else- 

 where, increasing from 27 inches in the northwest to 58 

 inches in the Ohio Valley. 



Phenomena particularly favorable to plant disease de- 

 velopment included the fact that 56 per cent of the year's 

 precipitation occurred during the crop growing season. 

 The number of cloudy days was greater only in 1915 and 

 the number of days with rain was greater onlv in 1898 and 

 1915. 



