WHITE-PINE BLISTER RUST. 85 
all the ground and pull the Eibes 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 killing 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 
a*s 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 quickly 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 New 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 still 
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 number of Ribes 
missed in the early work. 
