84 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 
disease is kept from attacking more pines within the area where the 
Ribes are removed, but it may spread to Ribes miles away, there to 
start new pine infections, each of which will act as a new center of in- 
fection in future years. This makes it practically impossible where 
both white pines and Ribes are native entirely to eradicate the disease 
after the seciospores are once set free. 
REMOVAL OF PINES. 
In all work where pines have been removed the Ribes have been 
absent or were also removed; hence, all this work is placed under 
" Eradication of advance infections." In some of the States, Ribes- 
growing sections are being established, and it is expected that 
white pines will be entirely removed from such areas. 
REMOVAL OF RIBES. 
Experiments on a large scale are in progress in all of the States of 
New England and in New York, Wisconsin, and Minnesota for the 
removal of all Ribes in certain areas, to determine whether it is 
practicable thus to protect valuable white-pine stands. 
Much work of this sort has been carried on during the past four 
years. Infected areas have been chosen and the Ribes removed 
under various conditions to show what possibilities there are in 
such work (23, 24, 25, 103, 104). The removal of all Ribes plants 
in a given area is a difficult matter. Wild Ribes offer the greatest 
difficulties. It is not humanly possible to find every plant in wild 
woodland; plants pulled up, if left touching the soil, may again take 
root and persist in a living condition; pieces of root crown and oc- 
casional pieces of roots left in the soil sprout and make new plants 
(23, p. 8) ; fruits on the pulled bushes fall off and start a crop of 
seedlings to replace the parent plant; seeds of old fruits already on 
the ground may germinate and start seedlings. Nevertheless, the 
results of this work are encouraging. Wild currants and goose- 
berries do not reproduce rapidly in an area that has been worked 
by an efficient crew. Thorough checking on 2,485 acres in 8 separate 
tracts previously gone over by eradication crews showed that on an 
average acre, 62 bushes (95.5 per cent) were destroyed in the first 
working and 3 bushes in the second working. Of the latter, two 
bushes were missed in the first working and one bush developed 
from seeds or sprouts. The remaining plants are so small that they 
carry but 1 to 2 per cent of the total Ribes leafage (24) . Moreover, 
they are usually so low or so covered with other vegetation that very 
few become infected, so that the work results in almost perfect con- 
trol of the disease. To judge from data at hand, control areas usually 
should be reworked within 10 years after the first working (25). 
Two principal methods of removing Ribes have been developed. 
Where Ribes are abundant the Ribes eradication crew has to cover 
