124 EXPERIMENTAL FARMS 



7-8 EDWARD VII., A. 1908 



The varieties usually most affected are tiae Greening and Northern Spy, but it 

 also injures the Baldwin and other varieties. 



BLACK ROT OF THE TOMATO. 



This disease did much damage to tomatoes in the vicinity of Ottawa in 1906, a! 

 large percentage of the fruit being rendered useless in some plantations. When the 

 disease begins to spread on the fruit, small roundish spots may be seen usually to- 

 ward the blossom end. These rapidly increase in size and the tomato becomes dis- 

 coloured and rotten at the parts affected. The spores are given off from dark mould- 

 like masses on the surface of the fruit, and these being scattered re-infect the fruit. 

 The disease also attacks the leaves. The Tomato Rot can be controlled by spraying 

 with Bordeaux mixture, beginning in the hot-bed and keeping the plants covered until 

 the fruit is nearly ripe. 



ONION BLIGHT OR MILDEW. 



(Peronospora Schleideniana.) 



In the Ottawa district onions have suffered during the past few years from the 

 attacks of the Onion Blight, 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 oft' they remain over winter there and 

 re-infect the young plants in the spring or early simimer. It will be readily seen that 

 it is important where the disease is troublesome to remove all foliage from the field 

 in the autumn and destroy it. Where possible, the onion should not be grown two 

 years in succession in the same field, and if possible two years should elapse 

 as these oospores retain hfe for two years. When the disease infects tlie 

 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 dis- 

 ease is a violet discoloration of the foliage. In a short time the leaves turn yellowish 

 and fall over and give the plant the appearance of being scalded. When the disease 

 is quite apparent, but before the leaves dry up, the latter have a downy look on the 

 surface in places. It is at these 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 favourable will germinate in half an hour and 

 re-infect other leaves or plants. The 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 moistcr 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 important to check it at the very start or use preventive measures. 



Once the spore has germinated and the disease entered the leaf it is not possible 

 to reach the mycelium by spraying, hence it is necessary to spray early enough to kill 

 the spores before they germinate. Spraying should be begun towards the end of June 

 and the plants kept covered with Bordeaux mixture until the end of the season. If 

 the disease appears before spraying has been done^ spray as soon as possible. As the 

 leaves of the onion are smooth it is necessary to put the mixture on in as fine a spray 

 as possible so that it will adhere well. 



