< I.VH HOOT OK ( HIH'IFERS 



105 



Youiiir sfcininjis may often tii- infccti-d and not 

 show rocoiinizalili- symptoms of tlu- disfjiso at the 

 timo of tr.inspl.iiitinir. C anful tx.-miination of tin- 

 plants at tin- tiino of removal from tlic seed lii-ds is 

 therefore essential if there is any suspicion that the 

 disease may be present. Should a single seedling 

 from a seed frame show symptoms of club root it is 

 advisable, in the opinion of Sehlumberffer ("1 !■), 

 Chupp ('2->) and (Heisberg ('2(>). to avoid or de- 

 stroy all plants from tliat particular bed. since it is 

 only rarely that infected seedlings recover. 



Seed, Seed Bed and Seedlitifi Disinfection. — Seeds 

 of infected crucifers occasionally bear the fungus 

 spores externally, and in such cases seed steriliza- 

 tion is necessary. Soaking seeds in tillantin B and 

 0.25 per cent to 0.5 per cent usi)ulun for one-half 

 to one hour before planting has been reported by 

 Mothes ('25). Bronnle ('2(i) and Leines ('26) to 

 reduce the incidence of infection if followed by fun- 

 gicidal treatment of the soil. Such seed treatment, 

 however, is wortliless unless it is followed by seed 

 bed disinfection. 



^'arious fungicides and chemicals as well as heat 

 have been used in seed bed disinfection. Heating 

 the soil 1^2 hour at 60° C. or above kills the spores, 

 according to Vladimirskaya, Jorgensen, and Shew- 

 ell-Cooper. Commercial formalin (1 part to 10), 

 0.05 per cent to 0.2 mercuric chloride (1 to 2 gals. 

 per sq. yd.). 0.1 per cent to 0.5 per cent liquid 

 ceresan. corrosive sublimate (1 oz. in 2-10 gals. 

 water). 0.5 per cent uspulun solution, uspulun and 

 solibar mixed (1 to 5). 10 per cent solution of wash- 

 ing soda, folosan and brassiean ( 1 8 oz. per cubic yard 

 of soil) mixed with lime, carbolic acid, mustard oil, 

 etc.. applied 1 to 5 times to seed beds have been re- 

 ported to reduce or completely control seedling in- 

 fection bv the following workers: Anony. (Australia, 

 ■-to), Somnier ('22). Jorstad ('23). Bremer ('23- 

 '2 1). Darnell-Smith ('24). Kind.shoven ('24). 

 Chupp ('25), Hofferichter ('26). Clayton ('26), 

 Blunck ("28), O.sterwalder ('29). Preston ('30), 

 Hoffman ('32). .Jorgensen ('33). Gibbs ('34), 

 Woodman. Benchley and Hanley ('34), Kiipke 

 ('35). and Smieton ('39). 



Effective control has been reported from the use 

 of uspulun on seed beds, but some workers have 

 claimed that it is less satisfactory than mercuric 

 chloride. According to Clayton ('26) the spores of 

 /'. Brassicae in the soil are fairly sensitive to mer- 

 curic compounds, but such substances have been 

 found to be more or less toxic to the host, especially 

 in dry hot weather, and may reduce the cro]) to some 

 extent. Wellman ('30). however, found that mercury 

 compounds used according to Clayton's methods 

 were ineffective in Wisconsin unless applied in con- 

 centrations high enough to be injurious to the host. 

 Copper carbonate and sul))hate. and carbonates and 

 sulphates of calcium were likewise ineffective. Hy- 

 drated lime worked into the soil at the rate of 1 .500 

 pounds to 5 tons per acre gives good control in seed 

 beds, according to Wellman. Motte ('34) found that 



the fungus spores r;irely exceed a dc|)th of 20 cms. 

 in tlie soil, ;ind .-is a control measure for seed beds he 

 .Khoe.itfil rcmov.d of the upper 25 cms. of soil. 



.Seedling disinfection alone before or at planting 

 has not i)roven gener.illy i)r,ictic;il in controlling 

 club root. l)ii)|)ing seedlings uj) to the coll.ir in weak 

 solutions of uspulun, mixtures of uspulun ;ind solibar 

 solutions (1:5), mercuric eldoride. 0.1-1.5 i)er cent 

 liquid ceresan, etc., before planting has been recom- 

 mended by Kind.shoven ('24), Preston ('29), Rabbas 

 ('30). Kiipke ('35). and others, but Jamalainen 

 ('.•}6) asserted that seedling treiitment at and after 

 planting is ineffective. While such disinfectants may 

 inactivate the spores in the soil .idhering to the roots 

 and root hairs, they obviously cannot destroy the 

 amoebae and plasmodia within the tissues, if such 

 stages are already jiresent, without killing the host. 

 It is doubtful that enough fungicide will remain on 

 the roots during transplantation to kill or inactivate 

 the siJores which may be present in the plant holes. 

 Seedling treatment, as recommended above, must ob- 

 viously be followed by soil disinfection in the field 

 to be effective. 



The addition of 1 , 2. and 25 gms. uspulun dust per 

 plant hole (Esmarch, '25; Blunck, '28), 1 liter of 

 .25 per cent uspulun solution, 10 liters of .20 per cent 

 uspulun, tillantin B, and germisan per plant (Lind- 

 fors, '25; Hertel, '26; Rabbas. '30). 10-15 gms. 

 humus carbolineum per plant (Popp, '25), V2 pt. 

 .01 per cent (or 1 oz. in 6 gals, water) corrosive 

 sublimate per plant (Preston. '27; Holmes-Smith, 

 '30). chloropicrin in plant holes (Anony.. Rhode 

 Island. '39), 1/, pint .062-. 1 per cent mercuric chlo- 

 ride per plant (Pre-ston, '29; Olgilvie and Mulligan, 

 '34 ; Smieton. '39), and other chemicals have been re- 

 ported to reduce or completely control infection. 

 Preston ('28) found that Vj pt. per plant of .2 per 

 cent methyl green, malachite green, methyl violet, 

 and Brilliant green applied at planting was ineffec- 

 tive. Likewise clubicide and Clieshunt Brown com- 

 pounds as well as .2-.5 per cent formalin and .2 jjer 

 cent lysol were unsatisfactory for seedling treatment 

 at and after transl)lanting. 



Soil Disinfection in the Field. — In attempts to 

 combat club root in the field by soil disinfection a 

 wide assortment of chemicals, fungicides and spe- 

 cial remedies have been employed as is shown in 

 table 2 and the accompanying i)ages. In pots, seed 

 beds, small gardens, and ex|)crimental plots these 

 substances are fairly effective, but with the excep- 

 tion perliajjs of usjjulun they have not jiroven com- 

 mercially satisfactory and exi)edient in the field. As 

 Larsen and Walker ('34) have pointed out. green- 

 house pot tests are not always a true index of what 

 may be expected in the field. The cost of materials 

 and expense of apjilication often outweigh the bene- 

 ficial results obtained, and in many instances the 

 fungicides directly injure or reduce the ero]). Accord- 

 ing to Motte ('33) very little is now being done to 

 combat the disease in Denmark beside avoiding ma- 

 nure, using basic fertilizers, and growing resistant 

 varieties. 



