DEPARTMENT OF AGRICULTURE. 



'rol. From what has been said, it will be seen that the disease is spread 

 mainly by planting seed which is infected, or which has been in contact with infected 

 tub :iiplements. etc. In purchasing seed from the districts mentioned a: 



a guarantee should be required that no powdery scab has been found in the field, or, 

 still better, on the farm where they were grown. Seed-disinfection (sec under 

 "Common Scab'') should always !* practised. This will not render apparently 

 sound tubers from an affected crop safe to use for seed. as-.the disease may possibly 

 be present in such tubers in sufficient amount to affect the crop raised from them and 

 to infect the soil, and yet be in a form not reached by seed-treatment It will, 

 however. -:>ores on the surface, and therefore remove the risk of the disease 



being introduced on healthy tubers which have been in contact with containers or 

 implements contaminated with spores. Corrosive sublimate should be used for this 

 purpose in preference to formaldehyde. Sound tubers from an infected crop may be 

 disposed of for consumption if each container is plainly marked " Table potatoes 

 only not to be used for seed." Affected tubers, or tubers from an affected crop, 

 should be cooked before being fed to stock, otherwise the manure may be con- 

 taminated and the disease be spread to other fields. The same applies to parings 

 and other refuse from an attacked crop. These should not be thrown on the manure- 

 pile, but boiled or burned. Cellars, bins. bags. etc.. where diseased potatoes have 

 been should be disinfected with bluestone (copper sulphate). 1 Ib. to 5 gallons, or 

 formaldehyde, 1 Ib. to 1 gallon of water. Infected soil should not be planted to 

 potatoes again for five years. Farmers' Circular No. 5 of the Division of Botany. 

 Dominion Department of Agriculture. Ottawa, deals more fully with this disease 

 thai. !e here, and should be written for by those interested. (See note at 



head of this article.) 



RHIZOCTONIA. 



Tubers are very commonly found with what appear to be bits of hardened soil 

 adhering to them. Careful examination shows, however, that these masses of 

 foreign matter adhere very firmly, and on being moistened take on a black colour. 

 In size they may vary from that of a pin's head or less to *4 inch in diameter, and 

 may be very numerous. They may be detached with the finger-nail and the skin of 

 the tuber underneath will be found quite sound. These bodies (named sclcrotia) are 

 compact masses of the resting mycelium of a fungus commonly known as Rl 

 tonia. They do not cause any disease of the tuber, except perhaps in rare instances, 

 but they injure its appearance. If such tubers are planted, however, the resting 

 mycelium in the sclerotium iri\ an active form which may work much 



injury in the growing crop. In niai. ie sprouts are killed before they get 



above ground, this being one cause of potato failures. Later in the season various 

 symptoms may apitear. Some stems may die prematurely, and on examination there 

 will be found at the base of the stem, usually at the ground-line or extending either 

 way from this, dead, brown, cankered areas, often extending right around it. In 

 cases where the stems have been more vigorous or the attack less severe, the girdling 

 may have only been sufficient to partially prevent the flow of sap downwards. In 

 such cases a cluster of small tubers may be found close to the base of the stem, and 

 very commonly small green tubers are formed above ground in the angles between 

 leaf and stem. These aerial tubers are very characteristic of the disease, but may 

 be produced from other causes leading to partial girdling; e.g.. the breaking of the 

 stem by wind. Another stage of the fungus in the form of a greyish mould on the 

 stems also occurs in late summer and produces spores, but the chief means by which 

 the disease is spread is by the planting of tubers bearing sclerotia. In addition to 

 potatoes, a large number of cultivated plants are liable to attack from this stem-rot, 

 with consequent dwarfing or wilting of the plant. "Damping-off" of seedlings in 

 the seed-bed is also often caused by this fungus. 



Control. When once present in the soil it is impossible to "starve out" the 

 fungus, since there are so many plants, including weeds, on which it can live. It 



