'4 DEPARTMENT OF AGRICULTURE. 



Infection of the tubers may apparently take place at any time if spores of the 

 fungus come in contact with them under conditions of sufficient moisture and 

 warmth, but it is facilitated by injuries which break the skin. Much infection may 

 take place at digging-time if the tops have not been dead long enough to ensure 

 the death of the spores also. Where the tubers have been piled in the field, and 

 covered with infected tops still producing spores, every tuber may become infected. 

 The disease may also spread extensively in storage if the tubers are kept too warm 

 and moist. 



Control. Avoid the use of infected tubers for seed, no matter how slight the 

 infection may appear to be. Where the disease bas teen at all severe, do not dig 

 until the tops have been dead at least a week. Cellars or other storage-places should 

 be kept cool, dry. and well ventilated. The most important measure of protection 

 consists in spraying the growing plants at proper intervals. Since the disease is 

 carried to the tuber from the tops, it follows that the checking of the disease above 

 ground will protect the tubers. The most satisfactory spray is Bordeaux mixture, 

 lime-sulphur having been found injurious. For earlier sprayings a strength of 4-4-40 

 may be used; for later ones, when the disease is liable to become epidemic, 6-6-40 

 is better. No definite data have been collected here as to the usual time when the 

 first infections are noticed, but generally, as far as this disease alone is concerned, 

 if the first application is made about the blossoming-time of later varieties adequate 

 protection will be afforded. The number of sprayings to be given will be governed 

 by conditions. In wet seasons, when the disease is liable to be severe, spraying every 

 week or ten days may be necessary to control it. Usually about three applications 

 are sufficient. Since the disease varies greatly in severity from year to year, being 

 very bad one year and perhaps almost absent the next, it was at one time questioned 

 whether spraying each year as a safeguard would be profitable, taking one year with 

 another. Extensive experiments have settled this point conclusively, since it has 

 been found that properly made Bordeaux mixture has a beneficial effect on the 

 foliage, enabling it to keep green longer and do more work. The result is an 

 increased yield, so that even if no blight appears the cost of spraying is repaid in 

 whole or part. In seasons when the disease is bad. spraying may make all the 

 difference between a good yield of marketable tubers and a total crop-failure. 



WART-DISEASE (Chn/*oph1ycti8 endob lotted). 



Also known by the names of potato-canker and black-scab. This disease is not 

 known to exist in Canada at the present time, and as a complete embargo is in force 

 against the importation of potatoes from any country where it is known to. occur, 

 we have grounds for hoping that we may remain free from it. The disease occur* 

 to a considerable extent in Great Britain and Ireland, and these countries are, there- 

 fore, included in the embargo. The attempt occasionally made to bring in small 

 quantities of seed-potatoes from these countries in the mails is illegal, and punish- 

 able with a heavy fine. As the disease is a very serious one. it is desirable that 

 growers should be able to recognize it, in order that they may report its presence 

 immediately, should it at any time be discovered. Circular No. 4 of the Dominion 

 Department of Agriculture, mentioned at the head of this article, gives a very good 

 illustration of an affected tuber. Anything suspiciously like this should be sent to 

 the Plant Pathologist for examination. 



COMMOX SCAB (Actinomyccs clirumoac 



This disease is so common that a description is hardly necessary here. The 

 most important of its characteristics will be pointed out in the consideration of the 

 next disease powdery scab. Common scab attacks the tubers only, aud varies from 

 a rough corky spot usually distinctly raised above the surface of the tuber, to an 

 irregular pit. Only one or two of these spots or pits may be present on a tuber, or 

 they may be so numerous that the entire surface is disfigured with them. The chief 

 injury lies in the unsightly nature of the scabby spots, which is objectionable to 



