EARLY PROBLEMS 



11 



transmitted the disease. This was a leaf hopper, Cicadula seznotata Fall."- ^ 

 The disease is not transmitted by means of the juice from diseased plants 

 but can be transmitted by budding or grafting portions of a diseased plant 

 on healthy plants. Either nymphs or adult leafhoppers can transmit the 

 disease, but the causative agent has to be incubated in the body of the 

 insect about ten days before the disease can be transmitted to a healthy 

 plant. 



Figure 4. Cicadula sexnotata. A, Nymph in the first instar. B, Nymph in the second 

 instar. C, Xymph in the fifth instar. D, Full-grown adult. 



In his first paper, he reports that the insect can transmit the disease to 50 

 different species of plants belonging to 23 families. In a later paper, he re- 

 ports 120 additional hosts belonging to 30 different families of flowering 

 plants. Dr. Kunkel showed that perennial hosts such as Plantago major L, 

 and Chrysanthemum leucanthemum L. carry the disease over winter and are 

 a source of infection for the annual China aster. The insect over- winters in 

 the egg stage, but eggs do not carry the disease. Aster yellows proved to be 

 the same as white heart of lettuce and an undescribed disease of buckwheat 

 and, of course, it is a disease on all the great number of hosts found giving 

 symptoms more or less similar to those on aster yellows. It is not identical 

 with peach yellows, curly top of beets, strawberry yellows, cranberry false 

 blossom, or Dahlia stunt. 



The symptoms of the disease on aster yellows are shown by the accom- 

 panying colored plate (Fig. 3). Fig. 4 shows four stages in the development of 

 the insect vector. The disease, of course, would not appear on China asters 

 in locations where no perennial or biennial carrier grew. Such regions are 

 scarce. The sure control is to grow asters inside of areas caged with cheese- 

 cloth or other screenings of 22 x 22 meshes to the inch or finer. Even in such 

 cages yellows plants must be rogued as soon as they appear. The discovery 

 of the method of transmission of aster yellows and the means of controlling 

 the disease led to a great revival of aster production commercially. The 

 cages not only prevent the disease, but the conditions \nthin the cages pro- 



