IMnVDKUY SCAH OF I'OTATOKS 



188 



may bo si-rurcd with liroadi'ast sul|ilmr than when it 

 is applied in drills. Cotton (''2'2) loiind tiiat tin- ad- 

 dition of (iOO lbs. per acre redueed the iiieideiiee of 

 infeetion from St to 7.5 per eent, while Hoiiiiif; and 

 Wallner ('3S) reported that the incorporation of 

 sulphur .it the rate of K)0 klg. per heet.ire with t)rdi- 

 n.-irv fertilizers diniiuished infeetion of the Parnas- 

 sia \;iriety from '2 ^ to 17 per eent. 



The .tiiditioii of eertain fertilizer ingredients to 

 the soil has also been reported to reduee infeetion. 

 Petliybridjie noted very early that the applieatiou 

 of superpiiosphate and sulphate of potash reduced 

 the number of diseased tubers, and later tliis asjiect 

 of control was investigated more thoroughly by Mel- 

 hus and his collaborators in M;iine. Each of fifteen 

 plots of soil of v.irying composition and texture were 

 fertilized seiiaratcly with sodium nitrate, old horse 

 manure, new horse manure, ijliosjihorie .icid. ammo- 

 nium suliihate and phosphoric aeid, ammonium sul- 

 phate and jiotassium chloride respeeti\ ely and tested 

 against 7 controls treated with commercial fertilizers 

 at the rate of 1..500 lbs. per acre and 7 untreated con- 

 trols. These plots were then seeded with Green 

 Mountain variety tubers which had been disinfected 

 with the usual strength of mercuric chloride. All of 

 the fertilizer ingredients tested alone reduced infec- 

 tion 5 to 12 per cent below that of the controls. Am- 

 monium sulphate and acid phosphate gave nearly the 

 same yields as the fertilized checks and diminished 

 infection 7.6 per cent, while potassium chloride 

 yielded the least infection, which may have been 

 partly due to the jirolonged growing season in this 

 case. 



So far no completely resistant and immune potato 

 varieties have been found or developed. Although re- 

 ports of partial to complete varietal resistance have 

 often been made, it is not certain whether the re- 

 ported resistance is due to inherent immunity or to 

 the fact that the jilants escaped infection. Soil com- 

 position and texture as well as the number of spores 

 present doubtless vary considerably, and it is not 

 improbable that these factors are often the cause of 

 variations in infeetion. This is probably true in the 

 ease of Melhus' experiments conducted in 1915 in 

 Maine. Melhus and his co-workers found four named 

 varieties (Ei.dohado, Farys. Wohltmann, and 

 Senator) and seven seedlings the tubers of which 

 were free of the disease, while otliers showed very 

 slight to severe infection. However, inasmuch as the 

 control variety, Grkkx Mountain, also showed wide 

 fluctuations in degree of infection, Melhus, et al., 

 concluded that the variations in varietal response 

 were partly due to the fact that some of the varieties 

 cscajjed infection. They further believed that the na- 

 ture of varietal resistance jirobably rcl.ites to the 

 abilitv to form cork cambium. Gomolyako ('30) re- 

 ported that SviTKZ, Dkodora, I'ihoi.a, Kihia. Pau- 

 NASSiA, Gavroneck and Ji'bel were least affected 

 bv powdery .scab in Russia, but he was not eertain 

 that tliev are consistently resistant. Naumov like- 

 wise rel)orted these varieties to be parti/illy resist- 

 ant, while onlv one, Rose of Milet, remained free 



of infection in l!).'t.'). Dorojkin ('Jfi) found no com- 

 pletely rcsist.ant conunerci.d varieties but regarded 

 .IiHF.i,, CoHHLKH. .•uiil Pahnassia jis wcaklv Suscep- 

 tible. However, eight varieties of Solaniiin from 

 South America jirovcd to be innnune, as well as nine 

 hybrids develo])ed by the Pan Soviet Institute of 

 Pl.int Breeding. Herogovoy ('39) reported that none 

 of tlie varieties tested at the Kief (luar.-iutine labo- 

 ratory were comjiletely resistant, although the de- 

 gree of infection w;is (luite low. The variety \\'ohlt- 

 ma.vn showed the highest degree of resistance and 

 was recommended for sub-sandy soil. 



It is obvious from these reports that varieties such 

 as Parnassia, Wohltmann, Svitez, Juhel, Pirola, 

 and Cobbler possess some degree of resistance to 

 ])owdery scab. Tlie use of these varieties in connec- 

 tion with other control measures such as ))roper soil 

 drainage, tuber sterilization, soil disinfection, etc., 

 will doubtless do much to alleviate infection with 

 powdery scab where it is particularly abundant and 

 destructive. 



Geographical Distribution of Powdery Scab 

 and Bibliography of I^iteraturc 



.Vnony. 1923. Bull. Agric. Algerie-Maroc. 2nd ser. 



29 : 69. 

 Cujoutantis, A. 1921. Rev. Path. Veget. Entom. 

 Agric. 1 I : 60. 



ARMENIA 



Rovdo, A. S. 1936. White Russ. Acad. Sci. Inst. 

 Biol. Sci. Minsk 1936: 39. 



AUSTRALIA 



Anony. 1927. -Jour. Dept. Agric. Victoria 25: 613. 

 1936, Ibid. 3t: 161. 1938, Ibid. 36: 301. 



Bald, J. G. 1911. Painphl. Coun. Sci. Ind. Res. Aus- 

 tralia 106. 



Darnell-Smith, Cj. P. Ann. Rept. Dept. Agric. New 

 South Wales. 1920-21: 27. 



Norwood. R. B. 1933. Queensland Agric. .lour. 40: 

 382. 



Noble, R. J. 1921. Agric. Gaz. New South Wales 

 35 : 883. 



Hccke. L. 1923. Wiener Landw. Zeit. 73: 273. 281. 

 Janchen, E. 1921. Oesterr. Zeitschr. f. Kartotfelbau 



1: 3. 

 Kock, G. 1922. Wiener I.andw. Zeit. 72: 82. 

 . 1927. Oesterr. Zeitschr. f. Kartoffclbau 



1927, no. 3. 

 Wahl, B. 192K Zeitschr. Landw. Versuehsw. Deut- 



Oesterr. 1921: 1-8. 



CANADA AND .MARITIME PROVINCES 



Dickson. B. T. 1922. 1 Ith Ann. Rept. Quebec. Soc. 

 Protect. Plants, p. 67. 



