246 CALIFORNIA VEGETABLES 



gus, which affects the vines and roots so that the growing potatoes secure too 

 little nutrition and fail to develop, thus looking like a bunch of grapes, hence 

 the name "little potato." These often appear above ground. The third is the 

 fusarium wilt, which also blights the vines and the roots and later the tubers, 

 which become diseased and are often destroyed. 



Scab and rhizoctonia are carried in the soil which has previously borne 

 diseased potatoes, and so contains the germs, ready to inoculate newly planted 

 seed. Both these diseases also carry on affected seed, germs which serve to 

 spread the destruction. These two evils are alike, in that seed affected by 

 either one yields to treatment, if immersed for two hours in corrosive sub- 

 limate, 1 to 1000 1 ounce to 8 gallons of water or in formalin, 1 ounce to 

 2 gallons of water. 



The rough eruptions (scab), so ugly in appearance, quickly reveal the 

 presence of scab. It does not reduce the yield, but so mars the tubers that 

 the price is materially lessened. 



The destructive rhizoctonia appears as specks of dirt from the size of a 

 pinhead to quite sizable patches. They are not dirt, however, for washing 

 does not remove them. We can, however, scrape them off with the finger nail 

 without wounding the potato, which we cannot do if the spots are scab. When 

 thus removed the potato is not wounded. Of course, scab, which often resem- 

 bles rhizoctonia, cannot be removed without breaking the tissue. 



The third fungus, worse than rhizoctonia and far worse than scab, is the 

 fusarium wilt. This blights the vine, kills the roots, stops growth and is fatal 

 to the crop. The vines die prematurely, and the potatoes which are not suffi- 

 ciently diseased to be observed on the exterior surface, will often show the 

 work of the fungus if a slice is cut from the stem end of the tuber. A dis- 

 colored spot, usually a ring on the cut surface, indicates that the disease is 

 present and that the seed is unfit to plant. The nematode called an eelworm 

 causes a rough, lumpy appearance of the skin and darkens the fleshy part, 

 especially close to the peel. The roughened surface quickly reveals this affec- 

 tion, and eelworm potatoes should never be planted. 



The tuber moth bores through the tubers and blackens the tissue. Keep 

 the potatoes well covered with earth during the entire growing season and 

 remove all, even the smallest, from the field as soon as dry after digging. The 

 potatoes should be placed at once in moth-tight sacks, as the moths continue 

 to work after the potatoes are stored, and thus it is imperative to carefully 

 guard against their presence wherever potatoes are stored. 



The foregoing troubles are to be avoided by planting healthy 

 seed in clean ground and they are contemplated in the law pro- 

 viding for certification of seed potatoes in the law of 1915, which 

 has been cited. A few other minor troubles may be noted. 



Potatoes Going to Tops. Sometimes potatoes "grow all to 

 tops" and have a great number of diminutive potatoes that also 

 sprout and grow more small potatoes. Excessive top growth is 

 generally due to over-stimulation of the plant during its early life. 

 This may be due to excessive use of stable manure applied too near 

 planting time or to the lack of adaptation of the variety to the local 

 conditions. Where this excessive top growth occurs small pota- 

 toes form but are not adequately enlarged by return flow from the 

 top in process of maturing. The reason why these small potatoes 

 take to sprouting instead of enlarging as they ought is due to the 

 fact that the plant starting vigorously with too much moisture be- 

 came afterward too dry and then starting again caused the small 



