DAMPING-OFF 1.X 1'UllEST NUBSEBIES. 3 



authors the most serious enemy encountered in growing softwood 

 cuttings in Germany, if distinct would be a further addition to these 

 generalized parasites. However, it is now believed (34) to be identi- 

 cal with Corticium rayutn. Common generalized parasites of older 

 plants, such as Sclerotinia ttbertiana, Sclerotium rolfsii (129), and 

 Thielavia basicola (47), capable of attacking roots or other parts of 

 older plants of numerous species, may also be considered among the 

 damping-off fungi when they cause the death of small seedlings, as 

 occurs, for example, in attacks by Sclerotinia libertiana on lettuce 

 (20, p. 28) and celery (103, p. 536) in seed beds. Further study will 

 probably result in multiplying almost indefinitely the number of 

 more or less important damping-off parasites, both of the specialized 

 and unspecialized groups, although the most important of the latter 

 type are probably already known. 



Most of the references in literature to damping-off describe its 

 occurrence in truck crops and the losses caused in these crops. Ac- 

 cording to Halsted (53, p. 342), weed seedlings are also very com- 

 monly attacked. Duggar (33) names lettuce, celery, cotton, sugar 

 beet, cress, cucumber, and sunflower as especially susceptible to 

 injury by the two most important damping-off organisms. Except 

 for the plant species in which damping-off by seed-carried parasites 

 is common, it appears that the economic damage from damping-off 

 is serious only with plants whose culture involves the raising of the 

 seedlings in crowded seed beds for subsequent transplanting. For 

 example, tomatoes do not ordinarily suffer from damping-off in the 

 field (TO), but the growing of seedlings in flats for subsequent trans- 

 planting is sometimes seriously hampered as a result of the preva- 

 lence of damping-off. This same principle holds in general for trees. 

 Broad-leaved trees, which are usually not as crowded in the seedling 

 stage as are the conifers, seldom give rise to complaint on the score 

 of damping-off. The conifers, subject to serious losses in nursery 

 beds, are not believed to be greatly affected in this country by the 

 better known types of damping-off under forest conditions (68) 

 except in the less common cases in which seedlings come up in close 

 groups from squirrel hoards, artificial seed spots, or similar sources. 

 A considerable number of broad-leaved trees have been reported at 

 one time or another as injured by damping-off, though complaints 

 of commercially serious losses are not common. The cases which 

 have come to the writer's attention are listed below : 

 Cause not determined : 



Orange (43, 108). 



Olive, in greenhouse at the University of California. 



Russian wild olive (Elaeaynutt sp.), serious at an Iowa nursery; oral re- 

 port by Mr. C. II. Bechtle, formerly of the United States Forest Service ; 

 at another nursery in the same region this plant was reported as very 

 little subject to injury. 



