Sugar Beet Leaf-hopper 



Normal individuals do not have the power to cause the disease. It 

 has been demonstrated quite recently that before a sugar beet leaf-hopper 

 can transmit curly-top it must itself become inoculated by feeding upon 

 a diseased plant. 



There seem to be many points in common between the carrying of 

 curly-top by these leaf-hoppers and the relation existing between certain 

 mosquitoes and malaria fever transmission. The micro-organism which 

 is now supposed to be the real cause of the disease must be taken up by 

 the leaf-hoppers while feeding on a diseased plant and then transmitted 

 to healthy plants during the process of feeding upon them. 



Fig. 26. Cross Section of Sugar Beet, showing Darkening of Rings caused by Curly-top 

 (After C. O. Townsend, Bulletin No. 122, U. S. Bureau of Plant Industry) 



Investigations, the results of which have just been published,* 

 emphasize the importance of clean culture as a possible means of con- 

 trolling this insect. 



These investigations show that without a doubt the wild host plants 

 of the beet leaf-hopper become diseased and that when fed upon by non- 

 virulent leaf-hoppers, these insects become inoculated and can and do 

 transmit the disease to healthy sugar beets. The plant experimented 

 with was a common mallow. 



METHODS OF CONTROL 



There is very little to be said regarding the control of this insect. 

 In fact there is no known method by which curly-top can be prevented. 



The practicing of clean culture and the working and burning over of 

 all possible hibernating places is always to be recommended, but even 

 this is not sufficient. Until more is known of the insect and its associa- 

 tion with curly-top we cannot hope to be able satisfactorily to prevent 

 the damage it causes. There are cases on record where early planting 

 prevented injury. This does not seem to be a sure remedy in all locali- 

 ties, however. 



*"Wild Vegetation as a Source of Curly-top Infections of Sugar Beets,'" Boniquit and Slake, Journal 

 of Economic Entomology, Vol. 10, No. 4 (1917). 



125 



