Dec. 9. i9i8 Seedling Diseases of Conifers 551 



only were attacked. It is reported on Austrian and Corsican pine, on 

 Piniis montana, and even on white pine (5). The same or a similar rust 

 has been reported on species of Abies (24). The alternate stage occurs 

 on poplars (Populus tremula, P. alba, P. halsamifera candicans, etc.), 

 and as it attacks stems as well as leaves, importation of poplar as well 

 as of coniferous nursery stock may introduce the disease. 



« 



WHITESPOT 



Light-colored shrunken lesions sometimes appear at the bases of the 

 stems of pine seedlings as a result of excessive heat at the soil surface. 

 The lesions (PI. B, fig. 4, 5) are characterized by shrinkage, light color, 

 definite limitation, and the fact that such one-sided lesions as occur are 

 usually on the south side of the stem. They have undoubtedly been 

 confused with damping-off in the past. Unlike damping-ofiF, the lesions 

 do not extend longitudinally until some days after their appearance 

 and then apparently only as a result of the invasion of the original lesion 

 by fungi. Upward conduction of water is not interfered with. Losses 

 are occasionally serious, especially where there is little shade or the soil 

 is loose and inclined to become dry at the surface. This type of injury 

 has been described in more detail by Miinch {ig, 20) and Hartley {15), 

 who present evidence as to its relation to heat. A case of damping -off 

 recently reported in red pine {18) in which the loss was limited to soil 

 containing raw humus allowed to dry at the surface may be an example 

 of confusion between whitespot and parasitic damping-off. Miinch 

 emphasizes the likelihood of heat injury on raw humus soils. 



MECHANICAL INJURIES 



Mechanical injuries of different types are rather frequent in coniferous 

 seed beds during the first month after germination. This is particularly 

 true of species which have small seed and therefore produce delicate 

 seedlings. Red pine, with a seed of intermediate size, is also very 

 subject to mechanical breakage because of the unusual brittleness of the 

 stems during the first two or three weeks after the seedlings appear 

 above soil. Counts of obviously mechanically injured seedlings were 

 continued throughout the damping-off season in beds of red, jack, 

 and western yellow pine in Nebraska, Kansas, and the Lake States, in 

 connection with seed-bed disinfection tests. A survey of the data on a 

 large number of the untreated plots taken at random shows that the 

 total loss from mechanical causes may vary from i to 10 per cent of the 

 entire stand, with losses of 3 to 3.5 per cent common, and below 2 per cent 

 or over 5 per cent rare. 



Types of mechanical injury which cause loss in the seed beds are (/) 

 the washing out of the germinating seed or of very young seedlings; 

 (2) the actual breakage of the stems by high Avind, hail, beating rain, or 

 the feet of birds or animals; (3) the eating or pulling up of the seedlings 



