46 MASS. EXPERIMENT STATION BULLETIN 227. 



only. The significance of this fact may, however, be questioned, and for 

 two reasons: (a) as used, neither treatment produced a large crop; and 

 (b) the usual practice of combining organic with inorganic nitrogen was 

 not included in the experiment. 



(3) Nitrate of soda proved to be better than sulfate of ammonia as a 

 carrier of ammonia when there was a deficiencj' of lime in the soil. Most 

 of our Valley soils are deficient in lime. If lime is supplied in sufficient 

 amounts, ammonium sulfate is as good as nitrate of soda for onions. 



(4) Moderate applications of lime in practically all cases were matched 

 by increased yields of onions. This response to lime was particularly 

 marked when ammonium sulfate and muriate of pot.ish were used in 

 combination. Moderate applications (1 to 2 tons) to onions lose most of 

 their effect within four years. 



(.5) There is little choice between muriate and sulfate of potash as 

 carriers of potash for onions unless there is a great deficiency of lime, 

 when the sulfate is preferable. 



(6) Onions have responded well to fertilizers carrying a large propor- 

 tion of soluble phosphates. A high proportion of phosphoric acid reduces 

 but does not do away with the need of lime. 



(7) From the standpoint of fertility, onions can be grown successfully 

 with large (30 tons) applications of manure. Fertilizers used in addition 

 to the manure have no additional advantage. 



There are three conclusions common to the groujis of experiments worthy 

 of emphasis. 



1. For continuous growth of onions on Connecticut Valley soils a com- 

 plete fertilizer is necessary. 



2. Complete fertilizers having a high ratio of phosphoric acid give 

 best results with onions. 



3. Moderate and frequent applications of lime are necessary for onions 

 on Valley soils. 



There appears to be little if any necessity of a choice of carriers for 

 ammonia, phosphoric acid or potash provided practice is in accordance 

 with these three conclusions. 



ONION BLIGHT or DOWNY MILDEW 



By A. VINCENT OSMUN 



This disease caused widespread damage to the onion crop of the Con- 

 necticut Valley in 1924 and 1925. The first authentic report of its oc- 

 currence in Massachusetts was in late Augu.st, 1924. It is probable, how- 

 ever, that it has been present within the state for a much longer period, 

 as it was reported many years ago from Connecticut, Vermont and New 

 York. Our growers have indeed long been familiar with a disease known 

 to them as "blight," the symptoms of which appear not to be different 

 from those of the disease here under discussion. The disea.se was first 

 reported in this country from Wisconsin in 1884. 



Onion blight is caused by a parasitic fungus known technically as Perun- 

 ospora schleideni. This is one of a group of fungi called Downy Mildews, 

 and hence the name Downy Mildew is often used to designate the disease as 

 well as the fungus which causes it. 



