48 A NNl'AL HKP( >KT> OF hKPARTMKNT OF AliRKTLTT'RK, 194 
j n [§39 at many locations where i< was present on Ribes in 19B8. 
One >uL r ar pine was discovered along Girder Creek on the Klamath 
National Fores! with four incipient cankers of 1937 origin. This 
infection increases to three the number of places where pines have 
been found infected in California and extend- the known range of 
pine infection in the State to some 14 miles south of the Oregon 
border. As the disease mcubates about 3 years on white pine before 
it produces aeciospores, any infections on white pines that may have 
taken place in the last 3 years were still in the developmental stn«:e 
and some of them probably will begin producing aeciospores for the 
first time next spring. 
PROTECTION OF WHITE PINE NLKSKKY STOCK 
The zones for blister rust control around 93 nurseries containing 
over 87.000.000 white pines were examined for Ribes during 1939. 
This resulted in the destruction of 85,915 Ribes on 40,393 acres, or an 
average of 2.1 bushes per acre. This represents a very low Ribes 
population in the protective zones around these nurseries and indi- 
cates that the trees are well protected from rust infection. 
The protection of white pine nursery stock assures the produc- 
tion of trees for forest-planting purposes that are free from blister 
rust infection. This phase of the control work is a service of value 
to both grower and consumer, as it provides for the distribution and 
planting of rust-free trees. As white pines are used extensively 
for reforestation in this country, a source of planting stock free 
from blister rust is of considerable importance to fore-try and the 
nursery trade. 
ERADICATION OF THE CULTIVATED BLACK CURRANT 
Work on the eradication of the cultivated black currant in white 
pine regions was continued. Most of this work was done in the 
North Central States. In the other pine regions the removal of this 
currant has been practically completed, although a few plants may 
be found annually for several years. The cultivated black currant 
is an introduced plant, highly susceptible to blister rust, and an active 
agent in the local and long-distance spread of the disease. It- 
eradication in white pine regions is a necessary step in establishing 
control of the disease. During 1939 this work resulted in the removal 
of 11.35°. Ribes niffi'iim plants from 2.15-1 locations. 
MAPPING OF WHITF PIN K STANDS FOR PKOTFCTION KKOM HI.ISTFR Kl ST 
White pine stands and their protect Lve borders aggregat ing 2,711,745 
acres were mapped in L939 for protection from blister rust. This 
work provided 56,196 man-days of employment. The map- are used in 
connection with Ribes eradication work to -how the location of pines 
worth protection, the boundaries of the protective zones, the character 
of the ground cover, and the approximate distribution and abundance 
<d Rib( 8. W ith ih:- information the supervisors of the Rib< s -eradica- 
tion crew- ciiii quickly locate work area-, determine the eradicative 
methods to be used, and distribute their labor to the best advantage 
in carrying out field operations. With the except ion <>f new planting 
