PAPERS OX BIOLOGY AND AGRICULTURE 135 



Spinacli blight is a disease similar to many other mosa- 

 ics and "yellows", in that it is cansed by some vims in 

 the juices of diseased plants which when transferred to 

 healthy plants produces the disease just as though para- 

 sitic organisms were present. At one time it Avas thought 

 to be a nutritional disease, but this has been disproved. 

 Similar symptoms often appear, however, when there is a 

 deficiency of certain essential elements such as potas- 

 sium. 



Symptoms. A typical blighted plant has mottled, mal- 

 formed leaves. The leaves are curled and wrinkled, the 

 plant is dwarfed and the general color is yellow in con- 

 trast to the dark green of the normal plant. The younger 

 leaves near the center of the jDlant show the most marked 

 SATuptoms. Unlike many other mosaic diseases, spinach 

 blight results eventually in the death of the plant. The 

 leaves finally turn yellow, become spotted with dead 

 brown areas and the plant soon dies. 



Aphids are the main and only important agents of 

 transmission. The disease is probably not transmitted 

 either through the root or by seed. The aphids which 

 attack the spinach feed upon many other plants, and the 

 disease virus not only lives in the insects when they are 

 feeding on other plants, but is transmitted through sev- 

 eral generations. For this reason when the disease is 

 once established in a region it is extremely difficult to 

 eradicate it. Attempts to control the disease by destroy- 

 ing the aphids have so far failed on account of the habits 

 of the insects and their enormous breeding power. 



The seriousness of this disease is indicated by the state- 

 ment of Dr. McClintock that the annual loss to the truck 

 growers of Virginia alone is between $200,000 and $400,- 

 000. Since there are large areas devoted to spinach grow- 

 ing in Illinois it is important that this disease be not al- 

 lowed to become prevalent. 



It is suggested that a survey be made of the truck re- 

 gions of the state to determine the extent of the disease. 

 If it is limited in its distribution to a few fields it may 

 be possible to abandon the gro^vth of spinach in the 

 neighborhood of these fields until the disease had disap- 

 peared. If the disease is widely distributed the only re- 



