WIITTE-PINE BLISTER RUST. 85 



all the gi'ound and pull the Ribes as they go. Where Ribes are 

 relatively scarce they are likely to occur only in certain favorable 

 locations. In such territory an expert scout covers the ground, 

 mapping it and indicating the Ribes areas to be worked by the crew. 

 In favorable localities this has proved successful and greatly reduces 

 the cost of Ribes eradication (25) . Experiments in the kiUing of 

 thick stands of wild Ribes with chemicals indicate that this method 

 (113) materially reduces the cost. 



Ribes eradication was started as early as 1909, but at that time 

 was limited to plantations of infected imported white pines and to 

 a safety belt of 100 yards around them. In 1910, the width of the 

 safety belt was increased in some of the States to 500 feet, and in 

 1915 in Massachusetts to 500 yards. In 1916, 600 yards was taken 

 as the safe width for all situations. Prior to 1919, facts concerning 

 the spread of Cronartium ribicola from Ribes to pines were not 

 definitely known. As a result of the investigations of the germina- 

 tion and dissemination of the sporidia the width of the Ribes-free 

 zone was set, in 1919, at 200 to 300 yards for average conditions 

 (25, 146). 



In 1917, when extensive areas were first cleared of all Ribes, lack 

 of experience in such work by all connected with the work greatly 

 reduced its efficiency, but even then it was found that the outlook 

 was not hopeless, although the cost of eradication of Ribes was too 

 high to be justified except where pine stands were valuable. Effi- 

 ciency has been steadily increased since then until it has been found 

 that men green in this work can be quicldy taught to find and destroy 

 at least 95 per cent of all wild Ribes plants the first time over the 

 ground (24, 25). A system of checking the work has been developed, 

 as well as a system of accounts, so that present results are quite ac- 

 curately known. 



The cost of Ribes eradication has been steadily reduced. In 1918, 

 105,977 acres were worked in New England at a labor cost of 44 cents 

 per acre. In New England and Now York the average cost per acre 

 including supervision in 1918, was 66 cents. In 1919, in New York 

 and New England, 252,114 acres were worked at an average cost per 

 acre of 54 cents, including supervision, and of 42 cents for actual 

 labor (24, 25). Improved methods are expected to reduce stiU 

 further this cost as, in New England alone, the cost in 1919 was 24 

 cents per acre, owing to the use of improved methods (24). 



The efficiency of Ribes eradication with respect to pine infection 

 will become evident as time elapses. Examination of areas where 

 Ribes were eradicated in 1916 and 1917 has shown no new pine 

 infections. This is in spite of the considerable nimiber of Ribes 

 missed iii the early work. 



