256 



Diseases of Ornamental Plants 



The diseases of ornamental plants affect the appearance of the plants 



and often check growth and flowering. 



Rose 



Many kinds of roses, are grown in Illinois — Rugosas, Ramblers, 

 Climbers, and Teas for outdoor decoration, and an endless variety under 

 glass for cut flowers. The distribution of the diseases here reported is 

 limited mainly to those found on outdoor plants. 



Powdery Mildew 

 Caused by Sphaerothcca pannosa (Wallr.) Lev. 



Powdery mildew covers rose leaves with a white, powdery, fungous 

 growth. When present in abundance it attacks the young shoots and 

 leaves, and causes their dwarfing, curling, and malformation. It is often 

 serious on cuttings in the greenhouse. 



It was first reported in Illinois by Seymour, who collected a specimen 

 at Camp Point, Adams county, in July IS"; 9 and at X'illa Ridge, Pulaski 

 county, in 1881, and again in Cook county in the same year. 



At present powdery mildew on roses is known to occur in 68 coun- 

 ties, the distribution of which is shown on Map 119. It appears gener- 

 ally distributed over the state, and is especially common in both the ex- 

 treme north and the extreme sovuh. Something of its general occur- 

 rence may be inferred from the fact that the Survey herbarium now 

 contains more than 300 specimens of mildew, collected on cultivated 

 roses, including practically every type grown for outdoor decoration. 

 The Ramblers and Climbing roses seem to be most severely attacked. 



Mildew is readily controlled either indoors or out, by dusting the 

 plants thoroughly with a mixture of 90 parts sulfur and 10 parts lead 

 arsenate. 



Bl.\ck SroT 



Caused by Diplocarpoii rosac Wolf 



Black spot of the rose is a leaf disease, producing irregularly cir- 

 cular black spots on the upper surfaces of mature leaves. Those dis- 

 eased usually fall prematurely, and serious infections may prove de- 

 structive. 



At present, black spot is known to occur in 51 counties, distributed 

 as indicated on Map 120. It is wide-spread in the state and appears to 

 be commonest and most general in the southern tip and in the northwest 

 corner of the state. 



Many reports indicate that black spot is injurious to potted roses 

 in greenhouses, and this has been found to be true especially in Christian 

 and Logan counties. 



