478 DISEASES OF ECONOMIC PLANTS 



culent shoots, causing several centimeters of the terminal 

 portions to wilt and die. 



Bordeaux mixture is recommended. 



SPURGE 



Gloeosporiose {Glaeosporium ewphorhice Halst.)- — The 

 attack usually begins upon the flower cluster and passes 

 down the stem to the leaves, which then fall away, leaving 

 the naked, blighted branches. The disease often interferes 

 seriously with the ornamental effect of this decorative 

 plant. 



SUNFLOWER, ARTICHOKE 



Rust (Puccinia Helianthi Schw.). — Both wild and cul- 

 tivated species of sunflowers are often badly rusted. The 

 early sori are yellow to brown, the later black. Badly 

 rusted leaves die, curl, or fall, and much injury follows both 

 to flower and seed. 



In the spring the cluster-cup stage is sometimes found 

 upon the same host. There is some doubt as to the ability 

 of the rust upon one species to infect all of the other species 

 of host. 



Burning of infected refuse is the only remedy known. 



VERBENA 



Powdery mildew {Erysiphe cichoracearum DC). — 

 Powdery mildew is quite common upon verbena under 

 glass or in the open. 



The use of potassium sulphide, 1 ounce to 3 gallons, twice 

 a week has proved effective. 



