4 BULLETIN 453, U. S. DEPARTMENT OF AGPJCULTTTBE. 



have any value whatever. To secure aeration the best eastern 

 nurseries leave their beds entirely open to the wind, or, if side walls 

 are needed to exclude seed-eating animals, they use wire netting 

 only. Yet, at a nursery in western Kansas, after trying the rather 

 expensive netting sides, it was found by forest officers that as good 

 or better results were obtained by using beds with tight board sides. 

 It is well known that excessive moisture and shade must be avoided 

 in the seed beds. However, in sandy soils or in a dry country there 

 is nearly as much danger of getting the beds too dry as of keeping 

 them too wet. Drought often kills large numbers of seedlings in 

 beds left without water. 



Aside from common drought injury the effort to keep seed beds dry 

 may result in an entirely different type of trouble. If seed beds are 

 insufficiently shaded and the soil surface is not kept moist, there is 

 at some nurseries serious loss from "white-spot" injury. This injury 

 in seedlings up to 3 weeks of age appears as a whitening and shrink- 

 ing of the stem just above the ground line. The shrunken area in 

 most cases girdles the stem, the seedling falls over, and death follows. 

 When the injury occurs on one side only it is usually the south or 

 southwest side of the stem that is affected. The symptoms are very 

 much like damping-off, the decided white color of the part of the 

 stem first affected being the most noticeable difference. This white- 

 spot injury is caused not by parasites but apparently by heat, with 

 which possibly may also be combined the direct effects of intense 

 light. The temperature at the surface of a dry, loose soil exposed to 

 the sun may exceed 140° F., a very high temperature for most tender 

 plant tissues to endure for any length of time. White-spot injury is 

 almost always mistaken for damping-off, and has been observed to 

 kill more than half of the seedlings in unshaded beds of even so heat- 

 resistant a species as western yellow pine (Pinus ponderosa) . In 

 withholding water and shade from coniferous seed beds, nurserymen 

 must be very careful or the loss from drought and white-spot will 

 much exceed the advantage from decreased damping-off loss. Keep- 

 ing the beds dry is impossible in wet weather and dangerous in dry 

 weather, and it therefore will never be more than a partial control 

 method for damping-off. 



FERTILIZERS. 



The relation between soil fertilization and damping-off has been 

 but little investigated. In preliminary tests dried blood and nitrate 

 of soda have apparently favored the damping-off parasites, and their 

 use on pine seed beds is considered inadvisable. However, in Ver- 

 mont 1 tankage has given excellent results against damping-off. It 

 is evident that further tests of nitrogenous fertilizers are needed. 



1 Giflord, C M. The damping-off of coniferous seedlings. Vt. Agr. Exp. Sta. Bui. 157, p. 170. 1911. 



