1919] DISEASES OF PLAIsTTS. 351 



trees survive longer than younger ones, which should be protected first to in- 

 sure their reaching a marketable size. Cultivated black currants are specially 

 susceptible to the disease, which is not prevented or cured by spraying on cur- 

 rant, gooseberry, or pine. 



The activity of the connnittee has been extended to cover other new and in- 

 troduced plant pests. 



Status of white pine blister rust control in 1918, S. B. Detwiler {Amer. 

 Plant Pest Committee Bui. 2 [1919], pp. ^-i^).— This is a discussion, according 

 to territorial sections or regions in the United States and Canada, of white pine 

 blister rust and of matters relating to its control. 



It is thought tliat thorough scouting and removal of Ribes once in five years 

 in a space one-third of a mile wide around a pine growth will afford adequate 

 protection to areas affected. In Khode Island pastures where sheep were kept 

 no Ilibes were found even when these plants were abundant in areas of the 

 same sort immediately adjoining. Apparently the majority of wild Ribes seeds 

 are scattered by birds and squirrels. Observations made in New York con- 

 firm the opinion that wild gooseberries will not sprout if the crown is completely 

 removed, although skunk currants and swamp black currants have underground 

 stems which start new growth if not completely removed. 



A summary is given of Ribes eradication on demonstration control areas in 

 different States. It is thought that the hope of saving the western white pine 

 forests from infection lies in the enforcement of the Federal and State quaran- 

 tines against 5-leaf pines and Ribes. 



Results of scouting in Canada are considered to show that the blister rust 

 can not be eradicated at once from large areas where it is already abundant. 

 Small trial areas are being systematically worked to determine whether or not 

 white pine can be grown successfully in selected areas where the disease is 

 present. 



Scientific research and field investigations in 1918, P. Spaulding {Amer. 

 Plant Pest Committee Bui. 2 [1919], pp. 11-13). — This contains a summary of 

 the reports given by members of the Office of Forest Pathology, Bureau of Plant 

 Industry, U. S. Department of Agriculture, regarding scientific studies on the 

 white pine blister rust as carried on in 1918 at several places named. 



Air currents are important agents for the dissemination of reciospores, which 

 were found in ti-aps 2,700 ft. above the nearest known source, which was 5i 

 miles distant, this and other facts evidencing the extreme lightness of such 

 spores. Apparently spores produced on pine are much more widely distributed 

 than was formerly supposed. A large percentage of these will germinate even 

 after a period of several weeks. 



The spores of the early sumer stage on Ribes are much less widely distributed 

 than has been supposed, 100 to 300 yds. being a common distance, and one-third 

 of a mile somewhat miusual. They also retain their germinating power for a 

 shorter period than do the spores produced on pines. A period of several rainy 

 days is quickly followed by a new output of spores on Ribes. Studies from Ribes 

 back to pine have not yet reached a very satisfactory stage. 



The width of Ribes free zones necessary to protect the pines will vary from 

 100 to GOO yds. according to various conditions. Moisture is supposed to be an 

 important factor in the survival of teliospores. 



Overwintering of the uredo stage and resulting inoculation are considered as 

 fully established. The incubation period on pine appears to vary from about 

 IS months to 15 years. 



A Cronartium on Ribes in Colorado has been shown to be distinct from C. 

 ribicol<i, and has been named C. occidentale. It attacks none of the 5-leaf pines 

 and so far as known only the pinon pines {Pinus motwphylla and P. eduUs). A 



