DIVISION OF BOTANY 485 



SESSIONAL PAPER No. 16 



The plots were carefully watched during the season and records made, and 

 finally the crop was lifted October 18th. 



Careful examination of the crops showed that while there was considerable 

 variation in the yield from the different plots, owing mainly to the variable quality 

 of the soil, there were no constant differences between the plots differently treated in 

 regard to seed or on limed or unlimed soil respectively. The only constant differences 

 seemed to be in varietal freedom from and resistance to disease, Carman No. 1 

 being almost free from rhizoctonia on the tubers, Bochester Bose showing only a 

 very little, and Empire State and Gold Coin showing little and a good deal 

 respectively. In the standing crop no differences between the different varieties were 

 observed in the matter of susceptibility to the disease. 



POTATO SCAB EXPEEIMENTS. 



Another series of experiments carried on with a view to controlling the common 

 scab of the potato were outlined and given in charge of my chief assistant, Mr. J. W. 

 Eastham, B.Sc. who herewith reports the results in detail : 



The problem of treating land infected with the organism of potato scab in such 

 a way that the disease will be prevented or much reduced, has for many years engaged 

 the attention of experimenters. So far, however, no method has been found for giving 

 such a complete or partial sterilization to the soil, as would, at the same time, be 

 applicable and remunerative under field conditions. In view, however, of the severe 

 attacks of scai> in many parts of the Dominion, and the frequency of inquiries 

 regarding it, an experiment was undertaken to test one or two recommendations that 

 have been made, and to try one or two substances not previously employed in this con- 

 nection, although known to be of value in controlling certain other plant diseases. It 

 seemed that the most promising substance in this category was chloride of lime 

 (bleaching powder), a substance which, being manufactured on a large scale for use 

 as a disinfectant, can be purchased comparatively cheaply (2c. per lb. in 400 lb. 

 barrels). It has, moreover, given good results on a small scale in the treatment of 

 Club Eoot, (Plasmodiophora) of Crucifers and certain other soil troubles. In the 

 experiments mentioned, it was applied at the rate of half a pound to a square yard, 

 either mixed with water or worked into the soil, which was then very liberally watered. 

 The hypochlorite, which is the active component of the bleaching powder, rapidly 

 undergoes chemical change with the production of substances harmless to plant life, 

 and plants may be put into the treated ground two weeks or so after treatment. As 

 the application of the substance in suspension or semi-solution in water, or even the 

 copious watering of the ground after its application in the dry state, would involve 

 an amount of labour prohibitive under field conditions in most cases, it was decided 

 simply to mix the dry powder as thoroughly as possible with the surface soil. 



Sawdust sown over the ' seed ' in the drills at the rate of 5,000 lbs. per acre has 

 been stated to be very successful in preventing scab (Experiments at Leeds University, 

 Eng., quoted by J. B. Pole-Evans in Agr. Jour. S. Africa 1 : 692-3.) As sawdust is 

 generally easy to procure, it was thought worth while to test its value. 



As sulphur has also been found of value, it was decided to use it on one plot in 

 the usual way, i.e., in the form of a fine powder sown with the sets, and also in the 

 form of concentrated lime-sulphur solution. 



The land selected for the purpose of the experiment was located at Orwell, P.E.I. 

 The soil was loamy, in a high state of cultivation and tolerably uniform in character 

 over the area employed. Scab had been very severe in the potato crop raised on this 

 land the preceding season, many tubers being completely covered with the excrescences 

 and, in the words of the proprietor, bearing more resemblance to ' toads ' than to 

 potatoes. Scab is, moreover very bad in many parts of the district owing partly to the 



