DAMPTNG-OFF IN FOREST NURfcKKIKs. 25 



would presumably kill all seedlings on the area treated, but would. 

 of course, be of considerable value in stopping at the outset such 

 mycelia as those which caused the damped-off area in figure 7. The 

 procedure would be of practical value only in cases in which damp- 

 ing-off was chiefly limited to a few large patches of this sort, a rather 

 rare condition in conifers. 



Copper sulphate solutions have been used on pine seed beds at the 

 time of sowing with considerable success at some nurseries (65, 67). 

 Except in a nursery in which the soil contained carbonates, it has 

 proved rather difficult to prevent injury to the pines. The trial of 

 some such combination of copper sulphate and lime as was used 

 by Spaulding (136) on the surface of pine beds before sowing, which 

 apparently prevented the damping-off of lettuce in some unpub- 

 lished pot experiments of Mr. J. F. Breazeale, is considered desir- 

 able. Treating seed beds with ordinary Bordeaux mixture has also 

 been recommended. Home (78) secured especially good results 

 against Corticium vagum in tobacco seed beds by heavy applications 

 of Bordeaux mixture, and Schramm (122) and Clinton (28) have 

 obtained indications of its value as a spray in preventing the damp- 

 ing-off of conifers. It is probably worth further tests in various 

 amounts of application. In tests conducted by the writer in 1912 

 and still unpublished, some advantage was indicated for Bordeaux 

 mixture as a surface treatment after soil disinfection with acid. 

 Zinc chlorid as a soil disinfectant has also been found valuable in a 

 number of cases (65, 67), but it is more expensive and apparently less 

 dependable than copper sulphate. 



Formaldehyde and sulphuric acid have been tested more fre- 

 quently than other disinfectants. The use of sulphuric acid on 

 coniferous seed beds was originated by Spaulding (136). The first 

 intensive experiments with this acid were reported by the writer (63) . 

 The first experiments with formaldehyde on conifers seem to have 

 been in the early greenhouse tests of Spaulding (137), repeated in 

 forest nurseries in 1907 by Jones (83) and Spaulding (136). Most 

 of the experiments with these two substances have already been sum- 

 marized (67). A report not mentioned in this summary is that of 

 Schaaf (119, p. 88), who obtained favorable results with the acid. 

 The great trouble with formaldehyde is its tendency to kill dormant 

 seed. The length of time which must be allowed to elapse between 

 treatment and sowing in order to avoid this killing varies with con- 

 ditions. Formaldehyde is more expensive than acid and seems on 

 the whole to have been less effective in disease control. Acid, on the 

 other hand (applied just after the seed is sown, which is found to be 

 the best time) , on a few soils has caused injury to radicles, which it was 

 at first thought could be prevented only by very frequent watering 

 during the germination period; while in a few cases, when cold 



