EXPERIMENT STATION BULLETINS. 



649 



cover two hills were used. These were set up in the potato rows before 

 the plants had broken through the soil.* 



The caged plants remained free from leafhoppers and plant lice 

 (aphids) until these were introduced later in the season. When burn- 

 ing of the foliage became noticeable in tlie field, leafhopper nymphs and 

 plant lice were placed upon the caged plants. The data obtained dur- 

 ing the three seasons are tabulated below : 



Table I 



Effect of the Leafhopper EMPOASCA MALI on Potatoes 

 Field Experiments - 1919 



Field Experiments - 1920 



Field Experiments - 1921 



*Cages were set up before plants broke through soil and covered two hills. No insects on plants prior to date leaf-hoppers or 

 plant lice were introduced. 1919 experiments were reported in Phytopath. 10:61-62, 1920. 



GREENHOUSE EXPERIMENTS 



Unmistakable evidence showing that leafhoppers are capable of 

 causing burning of potato foliage was obtained by experiments con- 

 ducted in the greenhouse of the Botanical Section of the Michigan 

 Experiment Station, East Lansing, Michigan, during the autumn of 

 1919 and winter of 1920-21. Adults of the last summer generation were 

 collected and allowed to produce a new generation of nymphs on caged 

 plants (Fig. 3) in the greenhouse, and these were used in the experi- 

 ments tabulated on following page: 



^Possible criticism might have been offered in Ball's experiments in that the plants were caged late in the season, and complete 

 freedom from "burn" was not maintained in the checks. 



