MEANS OF PREVENTION AND CONTROL 1 21 1 



4) In order as far as possible to ward off attacks on cultivated plants 

 produced by physical agents and parasites, prophylaxis must be based on 

 phosphatic manure, more or less assisted by an addition of sulphates. 



938 - Means of Control of Chrysophlyctis endobiotica, a Potato Pest in Ger- 

 many. — ScH-VFFNiT E. and Voss G., in Zcitschriit fur Pilanzcnkninkhciten, Vol. 26, 

 No. 3"^, pp. 183-192. Stuttgart, June i, 1916. 



I. — Experiments in Soil Disinfection. — The experiments were carried 

 out on fields over-run by the parasite, at Nederpleis, with a series of 

 chemicals in different degrees of concentration. The disinfection of the 

 soil was done between the loth and 20th February, the plantation of 

 tubers on the 25th April and the harvesting of the potatoes on the 29th 

 October, Each plot had an area of about 7 sq. yds. The means of disinfection 

 were : " Beta-Lysol ", sodium cyanide, chromium acid carbonate, " Flurasil ", 

 kainit, calcium cyanamide, sulphur and " Uspulun ". 



The kainit, calcium cyanamide and sulphur, as well as the mixtures of 

 these materials, were first spread and then hoed in ; the " Beta-Iyysol ", 

 sodium cyanide, chromium acid carbonate, " Flurasil " and "Uspulun" 

 were used in aqueus solutions. " Uspulun " is a preparation of mercury so- 

 luble in water : " Flurasil " is a compound of silica, fluorine and zinc. Both 

 the products are prepared in Germany. Each experiments was repeated 

 three times on plots situated at different points. 



The results of the experiments, which are summed up in a table, show 

 that none of the agents gives satisfaction in every respect. The best effect 

 was obtained with chromium acid carbonate, which, on the plots treated, gave 

 3.94% of diseased tubers, and 11.59 % of stalks and leaves infested. Next 

 come the plots which received a mixture of kainit and a large quantity 

 of calcium cyanamide with 7.65 % of tubers attacked and 21.37 % of diseased 

 leaves. The third place is occupied by plots which received sulphur or 

 " Flurasil " ; the first of these had 10.14 % of diseased tubers and 31.81 % 

 of leaf parts attacked, and the second 8.64 % of diseased tubers and 33.63 % 

 of stalks and leaves attacked. The other means of control " Uspulun " 

 (even in large doses), sodium cyanide and kainit produced no effect. 



If the soil is not uniformly and equall)' reachedt hroughout its parts, 

 the experiments rarely give a good result. Owing to this fact, the tubers 

 on certain plots treated were more infected than those of the check plots. 

 This year it is hoped that the drawback in question has been avoided by 

 careful distribution of the plots over the soil at the time of autumn tillage. 



To sum up, it may be stated that the disinfection of the soil appears 

 to be successful in some respects, and for this reason the writers will repeat 

 their experiments for several years. 



II. — Behaviour of the different varieties of Potato toivards the disease 

 — 69 varieties were tested. Each plot had an area of about 4.5sq. yds. 

 The potatoes were planted from the 25th April to the 30th May, and 

 lifted from the 6th to the 30th October following. 



The results showed that the following varieties remained immune from 

 the disease : " Jubelkartoffel ", " Pulsens Juli ", " Rote Delikatess-Niere " 

 " Reingold ", " Roma ", " Blaue Rheinische Rauhschale ", " Verbesser- 



