August, 1907 



THE CANADIAN HORTICULTURIST 



IX 



"W, 



Onion Blight or Mildew 



T. Macovin, Horticulturist, Experimental Farm, Ottawa 



IN some parts of Canada onions have sulTered 

 during the past few years from the attacks 

 of Onion Blight, I'cronospara Schleideniana, 

 which in some cases has caused serious loss to 

 vegetable growers. As this disease can be 

 prevented by thorough spraying with Bordeaux 

 mixture, all vegetable growers should be aware 

 of the fact. The onion blight is a parasitic 

 fungus which spreads by means of spores in 

 summer and is carried over winter by what are 

 known as oospores. These oospores are formed 

 within the leaves, and when these are removed 

 in the field or fall off they remain over winter 

 there and re-infect the young plants in the 

 spring or early summer. It will be readily seen 

 that it is important where the disease is trouble- 

 some to remove all foliage from the field in the 

 autumn and destroy it. Where possible, the 

 onion sliould not be grown two years in succession 

 in the same field, and if possible two years should 

 elapse as these oos|X)res retain life for two years. 

 When the disease infects the onion plants by 

 means of the oospores in early summer the 

 mycelium grows through the plants, feeding on 

 the juices, and the first outward indication of the 

 disease is a violent discoloration of the foliage. 

 In a short time the leaves turn yellowish and 

 fall off and give the plant the apjjearance of 

 Ix^ing scalded. When the disease is quite ap- 

 parent, but before the leaves dry up the latter 

 have a downy look on the surface in places. It 

 is at those points that the spores are being given 

 off from the tiny stalks which have protruded 

 from the mycelium within the leaf. These 

 spores spread rapidly and if conditions are 

 favorable will germinate in half an hour and re- 

 infect other leaves or jilants. These spores are 

 so numerous that it does not take long for a 

 large area to become affected. It has been found 

 that the disease spreads most rapidly in damp. 



warm, close weather, the spores germinating 

 very rapidly under such conditions. In low- 

 lying ground the air is moister than over elevated 



land, and the disease is usually worst there. 

 Sometimes the disease will be checked before 

 it has done much damage owing to a change in 

 weather conditions, but it may break out again 

 later on. Every leaf which is destroyed weakens 

 the plant and lessens the size of the onions, hence 

 it is very iniportantito check it at the very start 



'We'll Prove 

 To You 



that our sheet metal building materials are the 

 right kind — most durable, most satisfactory, 

 and most economical. Our "Book of References" 

 ^ will show you how our 



^ Sheet Steel Siding's 



^ 



have "made good" on many handsome homes. They give all the rich 

 appearance of brick or stone, at a much lower cost. They come in a great 

 variety of attractive designs. They make a house fire and lightning-proof 

 — warm and weather-tight — handsome and comfortable. 



A metal -clad house is the easiest to build. Anyone, who can handle 

 a hammer, can apply our steel sidings. There is no waiting or inter- 

 ruption from start to finish, when you build of metal. Move right 



in when the last nail is driven — ho;ise will 



be dry and comfortable. Let us send you Ji'^'jj^ 

 our Catalogue and "Book of References." 

 You'll be interested in knowing how to 

 build a better house than the ordinary, 

 and for less money. 



The Metal Shingle & Siding Co. Limited 53 



""? If''''" 



Preston* Ont. 



MeatioD The Canadian Horticulturist when writinc. 



