No. 6. DEPARTMENT OF AGRICULTURE. 75? 



of treatment is to use water barrels, setting them on boxes on the 

 ground where potatoes are to be spread for drying. When a barrel 

 has been filled with potatoes, the solution is poured on, and at end 

 of tr'^atment it is drawn off in buckets and jjoured into another 

 barrel of potatoes while the treated barrel is overturned on the 

 ground. This is speedier than bagging the potatoes and immersing 

 them in barrels of the solution, but the latter way may be made 

 slightly less laborious. 



Scab in the Soil. — When the scab fungus is in the soil, as is very 

 frequently the case in old potato sections, there is no treatment of 

 the seed that will insure a clean crop, but the effects of the ddsease 

 may be controlled in degrees varying with the character of the eoil. 

 Tn the first flush of success with the corrosive sublimate treatment 

 of seed, the claim was made that fertilizers and soils exercised no in- 

 fluence upon the development of the disease, but this is an error. 

 Seed potatoes that are suspected of any contamination with scab 

 should be given treatment to kill the germs upon them, and such seed 

 planted in infested soil will give a cleaner crop than untreated seed 

 will give, but still the product may be unmerchantable if the soil 

 conditions favor the multiplication of the germs already in it. Sus- 

 cess in the fight against potato scab must depend in part upon a 

 control of soil conditions that will bring the destruction of the germs 

 already in it. 



It was once held that the rational means of cleaning an infested 

 soil consisted in crop rotation, and such rotation is an aid, but we 

 now know that the germs live in a soil six or more years without a 

 potato or beet crop to feed upon. It is probable that the improve- 

 ment resulting from ceasing to grow potatoes in an infested soil for 

 five or six years is not caused by any "starving out" of the germs 

 through absence of potatoes as hosts for this fungus, but is due to 

 a change in soil conditions caused by some intervening crops. 



"Souring" the Soil. — My attention was called urgently to this 

 matter seven years' ago when one potato field in the farm had become 

 so full of the scab fungus that the crop was unmarketable. There 

 had been increase in scabbiness for a term of years. A farmer made 

 the statement in my presence that he never failed to grow a potato 

 crop free from scab w^hen planting in land that had had a winter 

 cover crop of rye. For seven years the experiment has been made 

 of growing a crop of potatoes in this field on a sod of fall-sown rye, 

 and the results have been very interesting in several ways. Inci- 

 dentally I may say that the yield this season of the seventh succes- 

 sive crop of potatoes was 285 bushels per acre, and during these 

 years little had been done to aid the rye in maintaining fertility ex- 

 cept to apply phosphoric acid in form of an acid phosphate. But 

 the experiment was conducted in part to determine something about 

 the control of scab in the soil. The seed was left untreated, and 



