UFA' OUT Or THE BOTANIST 257 



SESSIONAL PAPER No. 16 



Control. 



From what has been said above, it will be readily understood that complete 

 destruction of the refuse of the diseased crop is very desirable. In any case, contamin- 

 ation of the manure should be avoided since the resting spores retain their vitality 

 for a long time. Rotation of crops is also important, the disease being most destruc- 

 tive in regions given up largely to onion growing. In addition, spraying with Bor- 

 deaux mixture has been successfully carried out, beginning preferably before the 

 disease makes its appearance. Owing to the smooth, polished surface of the onion 

 Jeaf ordinary Bordeaux mixture does not adhere satisfactorily, and it is necessary to 

 use Resin Bordeaux, which is made up as follows: Boil two pounds of resin and one 

 pound of sodium carbonate (sal soda, washing soda) in one gallon of water till the 

 mixture is of a clear brown colour. Add this mixture to each forty gallons of stand- 

 ard Bordeaux mixture. It may be mentioned that the addition of one pound of resin 

 and one-half pound of sal soda, boiled in one-half gallon of water to forty gallons of 

 Bordeaux mixture, will greatly prevent this mixture from being washed off by rain. 



alfalfa leaf-spot (Pseudopeziza Medicaginis [Lib/] Sacc). 



This trouble, known as ' rust ' and ' blight ' is a very common and widely distri- 

 buted disease, being generally present in a greater or lesser degree wherever alfalfa is 

 cultivated. While frequently of little or no importance, it may become serious by 

 (.{.using an extensive loss of leaves, especially in dry seasons. The disease appears first 

 on the lower leaves and gradually spreads to the younger ones. An affected leaf shows 

 a number of small spots and, if these are numerous, the whole leaf soon turns yellow, 

 and falls away. The spots are brown or blackish in colour and circular, but the mar- 

 gin is not very clearly defined. The first cutting is not usually affected to the same 

 extent as the later ones. Young plants, however, may be so severely injured that the 

 crop is destroyed, whilst in any case the loss of leaves reduces the yield of hay directly 

 and also by reducing the growth of the plants. 



Control. 



No very satisfactory means of dealing with the pest under field conditions is at 

 present known. Where the disease appears severely early in the season, it may be 

 advisable to cut the crop at once. The subsequent growth of the plants in such a case 

 may escape the disease. Diseases attacking crops which are grown on so large a scale 

 that spraying becomes impracticable, as for instance rust, smut, alfalfa leaf-spot, etc.. 

 are not readily prevented. In small plots, one may succeed in preventing and even 

 checking diseases by various methods, but these cannot possibly be employed in large 

 areas iTnder crop. This procedure would be far too laborious, and hence too expensive 

 to be practised on a farm. But the farmer may, with comparative ease, select from 

 any diseased crop one or more plants practically free from attack and save seed from 

 these for propagation. If he perseveres in this manner ho may ultimately secure a 

 plot of disease-resisting plants, from which he finally may raise all the seed he. needs 

 for field sowing. 



club root of crucifers (Plasmodiophora Brassicae, Wor). 



(Plate III. a). 



During the past year, specimens of cabbages and turnips attacked with this 

 disease have been sent in from Nova Scotia, New Brunswick and Prince Edward 

 Island. Our records of its occurrence in the Dominion are confined to these prov- 

 inces but it is highly probable that it occurs elsewhere, Ontario farmers having inciden- 



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