Dec. 9, i9i8 Seedling Diseases of Conifers 555 



fallen over as a result of water shortage therefore exhibit uniform bending 

 of the entire stem, while seedlings fallen from damping-off or from white- 

 spot usually have a rather sharp bend in the lower part of the stem, and 

 little or none in the upper part. 



In a number of western commercial nurseries in which no provision is 

 made for artificial watering drouth injury is in certain seasons a serious 

 matter. During a normal season and in a loamy soil loss from drouth 

 in first-year seed beds is probably not a serious matter east of the Missis- 

 sippi River. In nurseries, first-year seedlings more than a month old 

 apparently suffer less often from drouth than 2- or 3-year-old seedlings 

 as they have their roots well established, but are not large enough to 

 crowd each other and rapidly exhaust the soil moisture. 



Soft-stemmed seedlings so far injured by drouth as to be badly wilted 

 may still recover if supplied with water within a few hours after wilting. 



SUMMARY 



(i) Damping-off is the most serious disease of very young seedling 

 conifers. A number of symptomatic types are described, part of which 

 are figured in Plate B. 



(2) Corticium vagum, Pythium debar yanum, and other oomycetes; 

 Fusarium moniliforme, F. ventricosum, F. solani, and other species of 

 Fusarium; Trichoderma spp. ; and Botrytis cinerea have been isolated 

 from damped-off conifers, and are believed to be able to cause the disease. 

 Spaulding's work indicates that Pestalozzia funerea can also cause damp- 

 ing-off of pine. In artificial inoculations on pines in autoclaved soil, the 

 first three species named proved to be especially virulent parasites. All 

 except Trichoderma spp. have given mere or less indication of parasitic 

 ability in inoculation experiments. 



(3) For Corticium vagum 12 coniferous hosts .are listed (p. 531). 

 One strain was maintained in artificial culture continuously for eight 

 years without perceptible loss of virulence. There is a marked difference 

 in virulence between different strains, which bears little or no relation to 

 the host from which the strain was isolated. For example, strains from 

 spruce and sugar beet, respectively, proved more virulent in inoculations 

 on pine seedlings than did any of the strains originally isolated from 

 pine. There was furthermore no indication that passage through seed- 

 lings and reisolation resulted in any increase in virulence. C. vagum 

 was found especially virulent in inoculations on a very sandy soil treated 

 with sulphuric acid, followed by lime. Slight virulence was indicated 

 in prelimi lary inoculations on untreated soils. 



(4) With the possible exception of Pythium deharyanum, Corticium 

 vagum appears to be the most important single damping-off parasite on 

 conifers, certain species of Fusarium also being probably important, and 

 the remainder of the organisms mentioned unimportant. The available 



