360 SEEDING AND PLANTING 



The writer for several years has had uniform success in preventing 

 loss from damping-off in spring-sown seedbeds by practicing the 

 following cultural method. After the seed is sown a deep hole is 

 excavated near the seedbeds and the subsoil from a depth of 

 two or more feet beneath the surface is used for covering the seed. 

 Pettis has used this method with success in the large New York 

 State nurseries. The author believes the above is the most prac- 

 tical cultural method for controlling the disease. 



9. BLISTER RUST. Several species of blister rust infest 

 various pines in the United States. They occur on the pine, how- 

 ever, in but one stage of their development, namely, the Peri- 

 dermium stage. They cause the greatest amount of damage to 

 young^ tree^in^nur^eries and plantations, often killing them in 

 large numbers. Older trees are rarely killed outright as infection 

 is confined to the smaller branches and twigs. Nursery stock is 

 usually infected on the stem near the ground. Infection may 

 occur when the trees are but one or two years old. It enters 

 through the bark and is usually slow_iiL- developing. Usually 

 one or more_yj3ars intervene after infection before evidence of 

 the disease shows on the surface of the bark. During this period 

 the infested stock is often shipped from nurseries without the 

 shipper or the recipient really knowing of its presence. This 

 condition of slow early development in the host makes the disease 

 a very difficult one to eliminate when shipments are permitted 

 from infected nurseries. The disease first makes its presence 

 known by a 1 perceptible swelling of the stem due to the thicken- 

 ing of the diseased bark. The swelling proceeds rapidly and 

 the following spring the fruiting bodies burst through the bark 

 setting free a multitude of yellow dust-like spores. If badly dis- 

 eased stock is shipped at this time clouds of spores arise from the 

 plants as they are unpacked. The disease is nearly always fatal 

 to young plants l as the infection on the stem gradually spreads 

 until the tree is completely girdled. 



Blister rusts indigenous to the United States have been found 

 on yellow pine, jack pine, and pitch pine nursery stock in New 

 England and to some extent on yellow pine in the West. The 

 great danger, however, from excessive losses in forest nurseries 

 in the United States from blister rust is due to the white pine 



1 Spaulding, Perley: The blister rust of white pine. (U. S. Bur. PL Ind..,. 

 Bui. 2 6, p. 16. 1911.) 



