EARLY SOWING ADVANTAGEOUS IN PREVENTING CURLY-TOP. 19 



generations in very alkaline soil and known, on that account, to be 

 much less vigorous than standard varieties sown in the main portion 

 of the field. These weakly strains occupied all of the small plat 

 except four rows next to the ditch ; the four rows comprised strains 

 of about ordinary vigor. On May 4 a small proportion of these 

 weakly seeds had sprouted; the weather continued cold and dry and 

 the seedlings were much retarded. On May 20 a few beet leafhoppers 

 were noted on this plat. By June 13 all of the beets had been 

 thinned. On June 27 eighteen cases of curly-top had developed 

 among the first few rows farthest from the ditch. The beet leaf- 

 hoppers appear to have started their invasion on that side, but at this 

 date they had become fairly well distributed over the plat. 



On July 9 ninety-five cases of curly-top had developed ; these were 

 mostly confined to the part of the plat wdiere the hoppers started. 

 These insects were now rather abundant. 



On July 20 the number of plants showing visible signs was the 

 same as on the 9th. Beet leafhoppers had greatly increased in num- 

 ber and were working over the entire plat. On the side nearest the 

 ditch the beets had become well established and of good size. After 

 this date the symptoms developed very rapidly, until on August 10 

 there were over three hundred cases. 



About mid-October, when the beets were dug, only a small per- 

 centage of them was free from signs of the disease. Every plant had 

 then been for some time infested by the insects. 



Early in August the leafhoppers had spread over the entire field, 

 but. except for a few cases on the edge of the ditch opposite the badly 

 affected plat, practically no plants in the main field exhibited visible 

 symptoms of curly-top. Few leafhoppers could be found in adjacent 

 fields or in the surrounding district, and cases of curly-top were rare 

 in those fields. 



The spring weather was unusually backward, with cold, driving, 

 winds through May and the greater part of June. The sky remained 

 overcast and light showers were frequent during the greater part of 

 this period. Until about mid-May only 0.15 inch of rain had fallen, 

 and the ground had become very dry. During the latter part of May 

 2.69 inches of rain fell ; during June, 3.28 inches. This was dis- 

 tributed in frequent showers of little weight. The strong, cold winds 

 soon dried up this moisture. It was not until July was well advanced 

 that really hot weather set in. During that month but 0.34 inch of 

 rain fell. 



EARLY SOWING ADVANTAGEOUS IN PREVENTING CURLY-TOP. 



Since it appears that very young beets or those in any way re- 

 tarded or rendered weakly are more likely to succumb to attacks of 



181 



