Chestnut Blight in the Southern Appalachians 7 
The infection spreads rapidly. In general, from two to six trees will 
be found blighted for every one which had the disease the preceding 
season. Since the severity of attack as well as the number of trees 
infected increases, the presence of the parasite rapidly becomes 
evident. 
_When approximately 80 per cent of the chestnut is attacked, the 
lalling effect of the fungus is shown by the presence of scattered 
dead and half-dead trunks as well as numerous dead limbs and 
branches. At this stage of the disease the lumberman and the farmer 
are usually aware of the need of prompt cutting. The class in which 
80 per cent or more of the trees is infected has been selected _as de- 
sirable for use in forecasting the spread of the disease. (Pl. VI.) 
There are two methods of predicting the time a given area will 
become 80 per cent blighted. By one method the percentage of in- 
fection in a locality is multiplied by an annual Actor, giving the 
period which may be predicted as required for that stand to be- 
come 80 per cent blighted. The second method consists in plot- 
ting the extension of the 80 per cent zone at the same rate it is 
known to have advanced in the past. In extending to the south- 
west across the State of Virginia this rate was approximately 24 
miles a year. Its extension to the west across the valleys and 
ridges was less rapid. In forecasting the future spread by this 
method allowance must be made for any outstanding spot infec- 
tions, for they, too, will throw out waves of the disease. In making 
the forecasts for the accompanying map (fig. 2), the two large spot 
infections, one in the Saluda Mountains and the other in northern 
Georgia, were allowed for. 
These methods have been combined in prepenns the forecast 
map. (Fig. 2.) Like the 1924 distribution map, from which it 
was prepared, the forecast map is not to be thought of as dealing 
with individual wood lots. It treats of the area as a whole. Nor is 
its accuracy, even as a whole, to be considered assured. It is based 
upon limited surveys and dependent on average conditions. The 
possible existence of large spot infections in counties not yet ex- 
amined or only partially covered is a source of probable error. At 
present it is believed that by 1930 well over half the counties of 
the southern Appalachians will be 80 per cent blighted and that 
by 1935 nine-tenths of them will have passed that stage. New fore- 
casts will be made when the available information from future 
surveys indicates that changes are needed. Owners of chestnut 
timber should make plans in advance to secure proper utilization 
before deterioration causes heavy losses. 
DETERIORATION 
A tree trunk girdled by the blight dies, just as girdled branches 
die; and, as with, the branches, the larger the trunk to be girdled 
the longer the fungus requires to kill the part. In general a large 
part of the chestnut in a blighted stand will die within from two 
to five years following the reaching of the 80 per cent infection 
stage. A few trees, however, will be blight-killed when the tract 
is 80 per cent infected, and others will not be dead six years after 
that stage is reached. 
