Pethybridge — The Verticillium Disease of the Potato. 89 



As regards losses, these are not easy to estimate, but for the whole 

 country they cannot at present be considered serious. Weighings were made 

 in 1914 of the yields of diseased and healthy plants growing under similar 

 conditions of cultivation on one and the same type of soil. The average yield 

 per plant of forty-seven healthy plants was thirty-six ounces, while that of 

 forty-two diseased plants was only twenty-seven ounces, so that there was 

 a loss of one-quarter of the crop owing to the disease. The plants were 

 growing in both cases in very poor soil, and in the absence of the usual 

 dressing of farm-yard manure ; and it is quite possible that in a rich and 

 well-manured soil the difference in the yields between healthy and diseased 

 plants might be still more pronounced. Hence if the disease by any means 

 became widespread throughout the country, the losses might be very 

 considerable. 



Since the disease is in all probability primarily contracted from the soil, 

 a proper course of rotation of crops should be followed, and potatoes should 

 not be cultivated for successive seasons on the same land. Where a diseased 

 crop has been grown the soil is almost certain to be contaminated thereby, 

 owing to the decayed and infected portions of the roots, rhizomes, and stalks 

 remaining in it after the crop is lifted. These portions of the plant contain 

 the fungus in them in its resting form ready to develop when the conditions 

 are favourable for it. It is a sound practice to burn potato-stalks when the 

 crop is lifted, as they may harbour not only the Verticillium disease, but also 

 other pests. 



The chief danger of introducing the disease into a new locality lies in the 

 use of infected seed-tubers. Growers of potatoes for seed purposes should 

 be particularly on the alert with regard to this disease. Should any affected 

 plants be observed in the crop, it would be best that the crop in such a case 

 should not be used for seed at all. If the affected plants are but few and 

 far between, each one should be dug out lock, stock, and barrel as soon as 

 possible. The tubers might be cooked and fed to pigs, but the foliage, stalks, 

 and roots should be destroyed, as far as possible, by burning. Should growers 

 have any difficulty in recognizing the disease, they should avail themselves of 

 the advice of technical experts, which is now so easily obtainable. Farmers 

 should scrutinize their seed-potatoes closely, and should look with suspicion 

 on any tubers which show a brown discolouration of the vascular ring when 

 cut across near the heel-end. Tubers showing this brown ring are not 

 necessarily diseased, but very frequently they are, and they should be 

 submitted for examination by a competent authority before being purchased 

 or used for seed purposes. 



It has been shown that all of the tubers produced by a diseased plant are 



