DAMPING-OFF OF CONIFEROUS SEEDLINGS. 31 



SUMMARY. 



(1) By damping-off is meant the killing of very young seedlings by 

 parasitic fungi. It is the most serious difficulty encountered in rais- 

 ing coniferous seedlings. 



(2) To decrease losses from the disease excessive moisture and 

 shade should be avoided. Caution must be used in following this 

 recommendation or many seedlings may be killed by drought or by 

 white-spot injury to the base of the stem. Damping-off can often 

 be decreased by putting beds on very sandy soil. Seed should not 

 be sown any thicker than necessary. It appears better to sow 

 broadcast than in drills. Late fall sowing results in decreased losses 

 at some nurseries and is worth trial. Proper attention to all of these 

 measures will decrease the losses from damping-off, but at most 

 nurseries they are not sufficient really to control the disease. 



(3) The addition of lime, wood ashes, and in some cases nitrog- 

 enous fertilizers seems to increase damping-off. Soil alkalinity 

 appears to favor the disease. No effect has been noted from green 

 manures. The use of unrotted stable manure has had very bad 

 results; properly rotted manures seem less objectionable. Tankage, 

 charcoal, and cane sugar are the only nondisinfectant substances 

 which to date have given any hope of disease control. 



(4) Soil disinfection has so far proved the best method of combat- 

 ing dam ping-off . Of many methods tested, treatments with sul- 

 phuric acid, copper sulphate, zinc chlorid, and formaldehyde have 

 proved the most satisfactory. The disinfectants behave quite differ- 

 ently at different nurseries. The results of treatments at many 

 different localities are summarized in Table III. The acid has on 

 the whole given the best results. Heat disinfection has been only 

 partly effective. Disinfection by acid or copper sulphate is cheaper 

 than by the other methods commonly recommended. 



(5) In addition to decreasing damping-off after the seedlings come 

 up, the chemical disinfectants above mentioned, when properly used, 

 cause an increase in the apparent germination and are very helpful in 

 controlling weeds. This latter effect alone at some nurseries pays 

 the entire expense of the treatment. Sulphuric acid has, further- 

 more, at some places resulted in marked increases in the late-season 

 growth of pines. (See PL II.) 



(6) In some soils formaldehyde kills dormant seed, and the other 

 three most satisfactory disinfectants at some nurseries kill the root 

 tips of germinating seedlings. By proper precaution, all such injury 

 may be prevented. 



(7) The results obtained to date show that it is entirely possible 

 and practicable to control damping-off by soil disinfection. Unfortu- 

 nately, the varying behavior of disinfectants at different places 



