20 THE CURLY-TOP OF BEETS. 



leaf hoppers, and since well-established beets show a decided resistance 

 to these attacks, it is obvious that anything assisting the establishment 

 of a vigorous and early stand of beets will at least render much less 

 severe the effect of an invasion of the beet leafhopper, should that 

 chance to occur. The plants may even entirely fail to develop curly- 

 top symptoms in the latter contingency, though they will inevitably 

 be checked in growth. However, should these insects be very nu- 

 merous and no means of speedily destroying or driving them away be 

 devised and put in operation, the beets, however large and vigorous, 

 will finalry succumb. 



A striking instance of the advantage of early planting is the fol- 

 lowing : Out of 13 acres of a single field, 10 were sown with beet seed 

 between April 10 and 15, the remaining 3 acres not being sown until 

 between May 10 and 20. Beet leafhoppers were abundant there that 

 season. The beets planted in May became so badly affected with 

 curly-top that only 2^ tons of beets per acre could be harvested. 

 From the 10 acres planted in April, 16 tons per acre were harvested, 

 few of the plants showing curly-top. The same kind of seed was 

 used and the same cultural methods, irrigation, soil, etc., prevailed 

 over the entire field. The disadvantage of late sowing and poor seed 

 is shown in the case recited as occurring in our small plat. 



EXTRACTION OF PLANT JUICES NOT SUFFICIENT TO ACCOUNT 



FOR THE DISEASE. 



That the profound disturbances induced in beets affected with 

 curly-top are not alone due to the extraction of plant juices by leaf- 

 hoppers seems obvious. A plant like the beet is able to withstand 

 the loss of much more juice than could be extracted by the few leaf- 

 hoppers that are necessary to induce a bad case of curly-top. The 

 writer saw hundreds of such insects as aphides and red spiders on 

 beet leaves, and the only apparent effect was a local leaf-curl, with 

 discoloration of the parts attacked, but no general and persistent dis- 

 turbance of the plant as a whole, except when the entire plant was 

 almost covered with these insects, in which case the plant was severely 

 checked and each infested leaf curled. But new growth on such 

 a plant is about normal if the insects are removed. The work of but 

 one leafhopper for a few minutes on a young beet has been shown to 

 be capable of inducing the curly -top symptoms. It therefore seems 

 obvious that some active agent is left in the plant tissues which is 

 capable of initiating profound disturbances. 



The writer has observed the symptoms only in growing tissue, 

 and not in mature leaves. Apparently all division is strongly in- 

 hibited. This inhibition seems to operate unequally, for, though the 

 growth of the leaf as a whole is checked, the vascular bundles seem 

 to be held back more than the parenchyma between the vascular 



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