756 ANNUAL, REPORT OF THE Off. Doc. 



tubers planted', aud the ground used is ground that has never been 

 used for potatoes, aud care is taken that refuse from a previous dis- 

 ease-bearing crop does not reach the soil of the new crop, one may 

 expect it to be free from the disease, 



'''Since the parasite is microscopic, one cannot be sure that there 

 are no spores of the disease on the seed potatoes, though thej ap- 

 pear to be smooth." 



Control of Scab. — Growers have observed that an application of 

 fresh stable manure, lime, wood-ashes and similar material very 

 often gives a scabby crop, and this is due to the favoring effect of 

 these substances upon development of the scab fungus. They can 

 not produce the disease, but they may put the soil into such condi- 

 tion that the scab germe in it multiply and thrive. On the other 

 hand there are materials that either destroy the germs or else create 

 such soil conditions that the germs do not grow. The results of Sta- 

 tion tests are very numerous and very conflicting, but the conflict 

 is largely due to the variation in soil conditions, and it is now pos- 

 sible to make an accurate statement of some of the truth about 

 the control of this disease. 



Treatment of Seed. — The germs of the fungus may be on the seed 

 to be planted, and not in the soil at all. When this is the case, a 

 fair degree of control of the disease may be obtained by the treat- 

 ment of the seed with a fungicide. Probably there is none superior 

 to corrosive sublimate. Under this head I quote Professor Green, 

 of the Ohio Station, Bulletin No. 76: 



"The usual recommendation for the treatment of seed potatoes is to 

 soak the seed for one and one-half hours in a solution of corrosive 

 sublimate, two ounces to tihirteen gallons of water. This treatment 

 is efficient, but so long an exposure to the solution reduces the vi- 

 tality of the potatoes somewhat, varying with the variety and condi- 

 tion of the seed. The matter of time at the busy season of the year 

 is of considerable importance, and this feature alone often prevents 

 the use of the treatment. For two seasons we have been soaking 

 the seed one hour only, and find the result to be entirely satisfactory. 

 Some experiments conducted last season indicates tihat the length 

 of time may be still further reduced, without detracting from the 

 value of the treatment. 



"Complaint has been heard that treated seed, if kept several weeks 

 before planting, loses its vitality. This may be true if the seed be 

 stored in tight boxes or barrels, without dr;>ing, but we have kept 

 treated seed in crates for several weeks without injury, although in 

 a cokl storage room, where the risk would be less than in a higher 

 temperature." 



Later experiments liave shown that forty-fi'S'ie minutes is a suffi- 

 cient length of time. In my own experience a convenient method 



