84 BULLETIN 957, U. S. DEPAETMENT OF AGEICULTURE. 



disease is kept from attacking more pines within the area where the 

 Kibes 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 OP 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 ofi^ and start a crop of 

 seedlings to replace the parent plant; seeds of old fruits already on 

 the ground may germinate and start seedlmgs. 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 



