fl.ni HOt)T OF (lll'l Il'KHS 



117 



I'ori'ciitdpe 

 Alknliiie of infet-tion 



5.55 gms. sodium nitrate 0-20 



10.50 " basic slaj; 

 13.11 " calcium carlionatc 

 i.li.) " jiotasli 



.\cid 

 i.-2 gm.s. ammonium sulfate 



8.9+ " supcrphosiihate 90-100 



17.S4 " jTj-psum 

 5.J5 " Kainit 



Controls 26- 31 



Plants treated witli tlie alkaline fertilizers showed 

 to 20 i)er cent infection, while those watered with 

 acid fertilizers were !»0 to 100 |)er cent infected. 



(iihhs ('32) also found a marked ditierence in cluh 

 root development when basic slag was compared with 

 superphosphate in conjunction with lime, as is shown 

 below: Percentage of Infection 



Seeds drilled Seeds drilled 

 with basic with super- 

 Treatment slag phosphate 



Control — no lime 59 95 



3 tons commercial ground 



limestone per acre 23 53 



3 tons superfine ground lime- 

 stone per acre 10 87 



2 tons air-slaked lime ])er acre 78 



2 tons burnt lime per acre ... 36 

 2 tons water-slaked lime per 



acre 3 82 



Kirschner ('27) has likewise advocated the use of 

 comjilete hasic fertilizer composed of basic slag and 

 potassium nitrate in conjunction with calcium cyana- 

 mide to control club root in the field. In this connec- 

 tion may be noted Pryor's ('10) study on the effect 

 of sulphur, nitrogen, and potassium nutrition on club 

 root develoj)ment in suscejitible, resistant and im- 

 mune strains of crucifers under controlled green- 

 house conditions in Wisconsin. Varying nutrition has 

 a pronounced effect on disease development in sus- 

 ceptible plants but does not influence resistance in 

 immune varieties, according to Pryor. An abundance 

 of potassium or nitrogen and a deficiency of sulphur 

 or nitrogen increased the disease in susceptible 

 plants. The percentage of infection was decreased 

 markedlv by a jiotassium deficiency. In the case of 

 resistant plants club root was increased somewhat by 

 a high supply of nitrogen ; increased further by a de- 

 ficiency of sulphur or nitrogen, and definitely de- 

 crea.sed by lack of potassium. 



Soil Drainage 



Since club root is frequently most severe on low. 

 wet and water-logged soils, proper soil drainage has 

 often been advocated as an effective cure. .Anderson 

 ('.5.5) and Ravn ('08) cited several instances where 

 club root had been markedly checked by drainage, 

 and Montieth ('21) and Naumov ('33) have demon- 

 strated by controlled experiments that crucifers can 

 be grown free of tlie disease in tlioroughly infested 



soil by keeping the soil moisture down to 30 to 10 

 per cent of the water-holding capacity ; all of which 

 indicates the effect of excessive water in the develop- 

 ment of club root. However, there is considerable 

 evidence to show the niainten.ince of proper soil 

 moisture bv drainage is not in itself effective. Severe 

 clubbing li.-is often been found on liigii. well-drained 

 soil and in fields which were carefully under-drained 

 with tile. Furthermore, Wellman ('30) has shown 

 that club root may occur generally in roots which are 

 exposed to only 18 hours of excessive soil moisture. 

 During the last two decades it has become increas- 

 ingly obvious that other soil fa<'tors, relative acidity, 

 humus content, etc., are involved and influence the 

 efficacy of drainage as a curative measure. \\'liile soil 

 drainage aerates and improves the physical condition 

 of the soil, it cannot be relied upon alone as an in- 

 Iiibitor, but must be used in conjunction with other 

 control measures to be effective. 



Crop Rotation 



Crop rotation is now generally recognized as es- 

 sential in combination with other control measures 

 against club root. Since the type of soil most favor- 

 able for intensive cultivation of crucifers is relatively 

 limited, farmers and gardeners have a tendency to 

 grow these crojis on the same land for several suc- 

 cessive years. If club root is present, such practice 

 obviously leads to heavy infestation with fungus 

 spores, and unless stringent control is exercised the 

 land may become worthless for crucifers within a few 

 years. "The earlier students of club root, including 

 Heinzelmann ('82), Eycleshymer ('91), Laubert 

 ('0.5a), Kock (']]), Burkhart ('1.5). and I.udwigs 

 ('25) advocated only 2 to 3 years between successive 

 crucifer crops, but since it has been shown that the 

 resting spores of P. Brassicae may remain alive in 

 the soil without hosts up to 7 and 8 years, it is ob- 

 vious that a long rotation period is necessary for 

 heavily contaminated fields. Jorstad ('23) recom- 

 mended 5 to 6 years, Lindfors ("21) 1, Siemaszko 

 ("25) -i to 5, De Andres ('29) 3, Nielsen ('33) 6 to 8, 

 Motte ('33) 7, Fedorintschik('35) 1, Gibbs ('39) 6, 

 and .Stubbs (H ) 1 years or more between successive 

 crops of crucifers. .Short intervals are aiijiarcntly in- 

 effective if Fedorintschik's observations that soil not 

 ))lanted to crucifers for seven years contain enough 

 viable spores to infect 26.6 per cent asceptically 

 grown cabbage seedlings are correct. The practice of 

 liming during rotation is of questionable v;ilue in 

 light of (iibb's ('39) observation th.-it the addition of 

 lime and sulpluir does not affect sjiore longevity. 

 Crop rot.ition is further com|>licated bv the fact that 

 wild cruciferous hosts or weeds are also susccjitible 

 to club root and may keep the fungus alive during the 

 rotation interval. 



\'arious cro|)S have been advocated as beneficial in 

 rotation. Halsted ('99) reported a fivefold increase 

 in turni))S on land whicli had been ])lante(l to buck- 

 wheat the previous season, but these beneficial re- 

 sults were not evident the second year. Pettera ('17) 



