250 DISEASES OF ECONOMIC PLANTS 



onion set seeding (about one fifth to one fourth as much for 

 field onions) ; or it may be apphed with a sprinkler so as 

 to well moisten the scattered seeds, which should then be 

 covered promptly with earth. 



Ground quicklime or stone lime, better the former, ap- 

 plied at the rate of 75 to 125 bushels per acre on the freshly 

 prepared soil just before seeding, has been useful. If ap- 

 plied by drill, harrowing will not be required ; if broadcast, 

 harrowing should precede planting. 



These methods used separately or combined are suffi- 

 ciently established to warrant general use on smutted soils 

 devoted to onions. 



Downy mildew, blight (Peronospora schleideni Ung.). — 

 Close kin to the disastrous blight of potatoes, this dis- 

 ease partakes of many of its characters, particularly in the 

 rapidity of its spread through an infected field. It may first 

 be noted on a small area of the field in which the tips ap- 

 pear as though dashed with scalding water. Often under 

 favorable climatic conditions the affected areas increase 

 manyfold in a single night, carrying complete destruction. 



It was first described in 1841 by Berkeley as " common 

 and destructive," and has been long known to onion growers 

 in this country, in Europe, and in Bermuda. In the latter 

 place it was so injurious that the legislature apphed to the 

 mother country for investigation and aid. The first refer- 

 ence to it in the United States was in 1872. It is now 

 known from coast to coast. 



The blight was described fully by Thaxter in 1889,* again 

 by Whetzel in 1904,^ during which latter year it was par- 



• Thaxter, R., Conn. Agr. Exp. Sta. Rpt., 1889. 



" Whetzel, H. H., N.Y. (CorneU) Agr. Exp. Sta. Bui. 218, April, 1904. 



