2 FARMERS’ BULLETIN 1641 
and cut out these advance infections to delay the spread of the dis- 
ease. The cutting-out work in Pennsylvania resulted in marked 
delay in the spread of the disease across that State. 
The blight has now extended to nearly all parts of the range of 
the native chestnut. In the extreme southern and western parts of 
its botanical range there are probably a number of small healthy 
stands of chestnut, but the steady spread of the blight means that 
these will be infected soon. The disease reaches isolated small stands 
of native chestnut that are many miles from any other chestnut or 
chinquapin growth. As the southern chinquapins are susceptible to 
the blight, these bushes will serve as hosts for the disease in localities 
where no native chestnuts grow. The percentage of infection in the 
southern Appalachians can be expected to increase steadily until 
the stand is foally killed. Table 1, based on observations on certain 
areas in Maryland and Virginia, gives a fair idea of the general rate 
at which infection and killing can be expected to increase, after the 
stand reaches the stage of 1 per cent infection. 
TABLE 1.—Rate of increase in chestnut-blight infection after 1 per cent infection 
has been reached 
[Percentages based on studies made on a number of areas in Maryland and Virginia] 
Infected . Infected 
Period after Sed ae 
infection infection 
reaches 1 per | eltby | tnrectea reaches 1 per | Healthy |tntected 
cent but not | Dead | Total cent but not | Dead | Total 
dead dead 
Per cent | Per cent |Per cent| Per cent Years Per cent | Per cent |Per cent|Per cent 
97 3 0 3, || 8 80 15 95 
90 10 0 10 1 69}* 30 99 
80 20 0 20 0 45 55 100 
60 40 0 40 0 25 75 100 
40 60 0 60 0 15 85 100 
20 78 2 80 0 10 90 100 
10 85 5 90 0 5 95 100 
PRESENT DISTRIBUTION 
The estimated distribution of the chestnut blight in the southern 
Appalachians in December, 1929, is shown in Figure 1, which is 
based ay on reports of cooperators and supplemented by very 
limited survey work by members of the Office of Forestry Pathology. 
The degrees of infection and killing are estimated upon a county 
basis, though the actual infection. within a county varies greatly. 
For example, a county having an average of 50 per cent of its trees 
blighted usually contains areas where the actual infection is less than 
5 per cent and others where it is over 95 per cent. In using the map 
it must be remembered that these figures on infected and killed trees 
are not the result of detailed surveys of each county but are merely 
Ses based upon the best available information in the fall of 
__No detailed records are available upon the prevalence of blight 
in the scattered tracts of chestnut timber in those parts of the South- 
ern States outside the Appalachian Mountains where the species is of 
minor importance. In a general way it is known that a major part 
