THE MONTHLY BULLETIN. 155 



is greatly in deniaiul, and he who produces this will top the market 

 in the prices he receives for his seed potatoes. 



There are two potent causes for the decline in our potato production : 

 diseased seed and infected soil. There are three fungous diseases that 

 are now very prevalent in our State, all of which atfect the potato, 

 tubers or vines, or both : the common scab, which disfigures the tubers ; 

 the Rhizoctonia fungus, which affects the vines and roots so that the 

 growing potatoes secure too little luitrition 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 Pusarium wilt, which 

 also blights the vines and the roots and later the tubers, which become 

 diseased and are often destroyed. These last two affections are much 

 more serious than the scab and are the principal factors in the destruc- 

 tion of the potatoes, not onlv in California but throughout the United 

 States. 



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. This is also true of Fusarium wilt. Both these 

 diseases also carry, on affected seed. hypha\ or sclerotia, which serve as 

 the seed 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 sublimate, 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, (piickly reveal 

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

 tubers that the price is materially lessened. The thick peel to remove 

 the disease is also a considei-able waste. 



The destructive Rhizoctonia appears as specks of dirt from the size 

 of a pinhead to quite sizable i)atches. We know that these are not 

 dirt, as their close adherence prevents removal when placed under the 

 hydrant. AVe can, however, scrape them off with the finger nail with- 

 out wounding the potato, which we can not do if the spots are scab. 

 When thus removed the potato is not wounded. Of course, scab, which 

 often resembles Rhizoctonia, can not be removed without breaking the 

 tissue. We should always treat the potatoes as described above if the 

 eruptive scab or the closely adherent Rhizoctonia is present. Indeed, 

 it is always a safe precaution to treat apparently sound seed, lest a 

 very slight infection is present, so minute as to escape detection. 



The thii-d fungus, worse than Rhizoctonia and far worse than scab, 

 is the Fusai'ium wilt. This blights the vine, kills the roots, stops 

 growth and is fatal to the crop. The vines die prematurely, and the 

 potatoes that survive affection, or are not sufficiently 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 discolored spot, 

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

 and that the seed is unfit to plant. We note then that the presence of 

 Fusarium wilt is shown in the meager crop, premature dying of the 

 vines and the discolored spot or ring on a slice cut from the stem end 

 of the potato. Such evidence should lead to rejection of all such tubers 

 for seed purposes. This disease is so prevalent in most parts of the 

 country tiiat even when we find no sign of its presence it is a wise 

 precaution to cut a generous slice from the stem end of the potato 

 before planting. 



