August, 1922 



SCIENTIFIC AGRICULTURE 



419 



and also from Provincial and Dominion De- 

 partments of Agriculture. No grower need 

 lack technical help to-day in this respect. 



2. Next to a knowledge of the diseases 

 to be controlled and how to control them 

 the most important point is to know thor- 

 oughly the variety or varieties most suitable 

 for the locality and the market. It is best 

 to grow only one or two varieties and to know 

 these so that "off varieties" can easily be 

 detected and rogued from the seed plot. 

 Grow a seed plot every year and select hills 

 for freedom from disease and for yield and 

 type. In arranging the seed plot choose 

 clean land, prepare it well, practise deep 

 plowing and rotation with legumes and cul- 

 tivate the potatoes thoroughly. 



3. As to the seed tubers themselves the 

 selection of thoroughly clean, sound tubers is 

 a prime requisite. Too many growers still 

 plant scab, black leg, blight, etc. and expect 

 to get potatoes. If it is impossible to obtain 

 first class, clean seed the next best thing 

 is to treat what is available. 



4. For seed tuber treatment two chem- 

 icals are available : — mercury bichloride 

 which is a deadly poison and formaldehyde 

 which is also a poison but which warns one 

 by the gas given off. 



Mercury Bichloride or Corrosive Subli- 

 mate Treatment 



Soak the seed tubers in a solution made of 

 4 ozs. of mercury bichloride in 30 gallons 

 of water for half an hour. If Black scurf 

 is present treatment for a longer period is 

 advisable according to the work of Howitt at 

 Guelph (see p. 236). The addition of one 

 ounce of mercury bichloride to the 30 gal- 

 lons of water after each sack has been treat- 

 ed will keep the solution up to strength. If 

 larger quantities are to be treated vats 

 should be used so that the tubers can be 

 handled in crates. It is important to re- 

 member that with corrosive sublimate (mer- 

 cury bichloride) no metal vessels can be 

 used. Treated tubers are poisonous to stock 

 and man. The corrosive sublimate can first 

 be dissolved in 2 gallons of hot water and 

 added to 28 gallons of cold since it is not 

 easily soluble in cold water. 



Formaldehyde Treatment 



1. Soak seed tubers for 1.5 minutes in a 

 .solution of formaldehyde made by adding 1 

 pint (or 1 lb.) of concentrated formalde- 

 hyde (commercial or 40 per cent.) to 30 

 gallons of water. 



2. A method recently tested by Melhus 



is recommended if the grower can arrange a 

 tank in which formaldehyde solution of 

 double the above strength is heated to 118° 

 to 122"F. In this case the tubers are soaked 

 for two minutes at this temperature and then 

 covered for an hour before cutting. 



5. If it is not convenient to plant im- 

 mediately after the completion of seed tuber 

 treatment, care must be taken that the treat- 

 ed tubers are not placed in sacks or containers 

 which have not been disinfected. 



6. When cutting the tubers discard all 

 rotted stock and also those tubers showing 

 browning or blackening in the vascular ring 

 at the stem end. It may happen that the 

 discarded tuber would give a healthy plant 

 but the chances are against it and "safety 

 first" is a wise saw. 



7. During tho growing season give the 

 plants good cultivation. 



8. Spray thoroughly with Bordeaux mix- 

 ture from tlie time the plants are eight inches 

 high. Make the applications about every 

 two weeks depending upon the weather. If 

 the weather is moist and warm and plants are 

 developing new leaves very rapidly they 

 must be covered with spray and hence spray- 

 ing may have to be done every ten days and 

 perhaps later during a drier spell at longer 

 intervals like 214 weeks. Spray before a wet 

 spell and use a fine spray which will cover 

 both sides of the leaves. Dusting is as good 

 as spraying for potatoes in most localities. 

 To control potato-chewing insects it is nec- 

 essary to add calcium arsenate or lead arse- 

 nate to the spray or dust. It is not necessary 

 here to deal with the preparation of Bordeaux 

 mixture or dust but any grower desiring in- 

 formation will be gladly accommodated if he 

 will write to Macdonald College. 



9. Finally greater care must be taken in 

 harvesting, handling and storing potatoes. It 

 is unfortunate that an excellent yield is some- 

 times spoiled in its last stages by bad hand- 

 lins. 



NOTES 



E. G. Hood (O.A.C. '13) Lecturer in 

 Bacteriology at Macdonald College, has re- 

 cently received the degree of Doctor of Phi- 

 losophy from the Massachusetts Agricultural 

 College. 



Dr. G. P. McRostie (O.A.C. '12 Cornell 

 '20). Associate Professor of Cereal Hus- 

 bandry at Macdonald College, has been apr 

 pointed Dominion Agrostologist at the Cen- 

 tral Experimental Farm, Ottawa. 



