2 CIRCULAR 7-17, U. S. DEPARTMENT OF AGRICULTURE 



crop plants, are hosts to many diseases, some of which are very 

 destructive. 



This circular brings together the information available on the more 



important diseases of pasture and forage grasses in the north-central 



region of the United States. Emphasis is placed on the distinguishing 



characteristics of each disease, and no attempt is made to include all 



the hosts or all the diseases known to occur in the 



region. No attempt is made to rank the diseases 



in the order of their economic importance. Grass 



diseases occur to a greater or less degree each 



year, with varying damage, depending upon 



environmental conditions and the manner in 



which the grasses are grown. 



i 



DISEASES OF PERENNIAL GRASSES 



KENTUCKY BLUEGRASS 



Powdery Mildew 



Powdery mildew, a fungus disease caused by 

 Erysiphe graminis DC, attacks many grasses 

 and is very common on Kentucky bluegrass 

 (Poa pratensis L.). It is a conspicuous disease. 

 The white powdery growth visible on the surface 

 of leaves is the vegetative and sporulating por- 

 tion of the fungus (fig. 1). Later, dried blotched 

 areas develop at the points where the fungus has 

 penetrated into the leaves. Severely infected 

 plants become weakened and retarded in growth. 

 Mildew is omnipresent and is seasonal in its 

 development. It first appears late in spring, 

 diminishes during the dry, hot period of summer, 

 and builds up again during the fall months. 

 Physiologic races of this fungus occur in nature. 



Figure 1. — Powdery 

 mildew on Ken- 

 tucky bluegrass. 



