70 THE DEPARTMENT OF AGRICULTURE. 



GENERAL PRINCIPLES IN THE CONTROL OF POTATO-DISEASES. 



(1.) Attack a disease as soon as it appears. 



(2.) Diseased crop refuse should toe burned. 



(3.) Avoid contaminated manure. 



(4.) Combat insects. 



(5.) Practise a rotation of crops. 



(6.) Keep down weeds. 



(7.) Keep crops in a healthy condition by manuring, cultivation, drainage, etc. 



(8.) Application of fungicides. 



(9.) Selection of seed use certified seed if possible. 



(10.) Sort potatoes carefully at digging-time, rejecting all injured or diseased 

 ones for shipping or storing. 



(11.) Where seed-disinfection is impracticable, have a seed-plot. 



(12.) Methods of prevention only are practicable, because as soon as a disease 

 gets within the plant nothing can be done. 



DISINFECTION OF SEED-POTATOES. 



This is of use only against external diseases such as common scab, powdery 

 scab, and Rhizoctonia,; it is useless against internal ones like late blight and wilt. 

 Pick over the potatoes before treating, rejecting those visibly affected with rots, late 

 blight, or badly attacked by scab or Rhizoctonia. Potatoes should be treated before 

 cutting. 



FORMALDEHYDE TREATMENT. 



Formaldehyde is a gas. The commercial article (also called formalin) is a 

 solution of this gas in water. In buying by measure, know what you are getting. 

 The usual druggist's pint is the American or wine pint, weighing 16 oz. The imperial 

 pint weighs 20 oz. Where large quantities are to be treated, it might pay to buy 

 co-operatively through farmers' organizations. The present wholesale price is about 

 $10 or $11 per gallon, imperial (about 10 lb.), while the retail price is about $1.25 

 to $1.50 a pound. It has a powerful hardening and corrosive action on the skin, 

 especially the stronger solutions, and the gas is irritating to the eyes, throat, and 

 nose. 



Effects of Treatment. This destroys spores adhering to the surface of the 

 tubers, tout the result will last only as long as the tubers are kept protected against 

 contamination. Formaldehyde, being a gas, evaporates, after which there is no 

 further protection from it. Hence, if treated tubers are to be dried and stored 

 instead of being planted at once, it is essential that the place of storage be also 

 disinfected thoroughly by swa'bbing down with formaldehyde, 1 lb. to 10 gallons of 

 water, or bluestone, 1 lb. to 10 gallons. A cement or board floor is preferable, and 

 this should be similarly treated. If only an earth floor is available, it should be 

 well swept, sprinkled with one of the above solutions, and then covered with sacks 

 or canvas soaked for an hour in one of them, or two hours in the dipping solution. 

 It would, however, in this case be better to treat just before planting and avoid 

 drying and storing. It is then only necessary to spread the treated tubers on dipped 

 sacks out-of-doors, and cut and plant as soon as the excess of liquid has drained 

 away. If more potatoes are treated than actually planted they are not injured for 

 human or stock food. Sprouted potatoes are liable to have the sprouts broken off 

 and the remainder seriously damaged, so that new sprouts have to grow. This puts 

 the crop back seven to ten days. Tubers intended for specially early yields must 

 therefore be treated before putting into the sproutiug-boxes, which should also be 

 disinfected. 



DIPPING. 



Add 1 lb. 40-per-cent. formaldehyde to 30 gallons of water. Put enough of this 

 into a barrel or other vessel to completely immerse a sack of potatoes.- With an 

 ordinary 40-gallon barrel this will take about 25 gallons. The remainder can be put 



