136 ILLINOIS STATE ACADEMY OF SCIENCE 



course is to develop disease resistant strains. For- 

 tunately the growers in Virginia have at present a strain 

 of savoy spinach which is highly resistant under their 

 conditions. This should be tried in Illinois, and if at all 

 resistant should be exclusively grown in the regions 

 where the disease occurs. A number of the growers 

 should organize to grow and improve the seed of this 

 strain and keep it pure. 



BLACKBEEEY * 



Powdery Mildew {Sphaerotheca liumuli (D. C.) Burr.). 

 On May 13, 1921, a number of mildewed wild blackberry 

 bushes were found near Odin, Marion County, Illinois. 

 Since no surface mildew had ever been observed on culti- 

 vated blackberry the specimens were carefully examined 

 to determine the species. It was evident that thsy were 

 Buhus alligheuieusis. No perithecia of the mildew were 

 found at this time. 



An examination of the literature revealed the fact that 

 no powdery mildew had ever been described on the com- 

 mon blackberry although reports of Sphaerotheca humidi 

 on the dewberry and other species of Rubus are common. 

 Burrill states that he collected a powdery mildew on 

 Rubus strigosus (dewberry) at Champaign and that 

 Earle had collected it on this host in Union County. They 

 did not find perithecia. 



It is probable that this mildew will never become a 

 serious menace to blackberry production under Illinois 

 conditions. The summer of 1921 was exceptionally favor- 

 able for powdery mildews. 



OAK (quercus.) 



Strumella canker {Strumella coryneoidea Sacc. & 

 Wint). This canker was found abundantly on oak at 

 Tonti, Marion County, in 1919. It caused girdling and 

 death of the twigs. It is not a very destructive disease 

 so far as the oaks are concerned, but since it also at- 

 tacks the chestnut and since this tree is grown exten- 

 sively for commercial purposes in southern Illinois, the 

 disease may assume considerable economic importance 

 in the future. 



