RUBBER (HEVEA) DISEASES 39 
insufficient aeration and frequent decay in the roots and the favor- 
able moisture factor in relation to spore production and germination. 
A noticeable case in point was the destructive effect of the fungus 
on several small trees growing in swampy soil as contrasted with 
the vigorous appearance of near-by trees growing on dry soil. The 
latter were also infected but had no dead branches. The leaves of 
the former were in all stages of infection and had many dead 
branches, with secondary fungi. 
The application of inhibiting substances by spraying or dusting 
would be difficult in the case of tall trees and large areas unless the 
use of an airplane was feasible. On nursery stock and young trees 
the disease may be controlled by spraying with Bordeaux mixture, as 
has been shown by Bancroft and Stahel. 
EXCLUSION 
Exclusion of the disease from regions of the most northern op- 
timum range of Hevea by establishing . plantations from seed or 
cuttings which, so far as known, do not carry the fungus and the en- 
forcement of strict quarantine regulations are worthy of consider- 
ation. Seeds and cuttings brought from regions where the fungus 
is known to occur should be treated. Care should be taken to avoid 
the use of twigs showing old cankers. Trees growing in Florida, 
Haiti, and Cuba have not yet shown signs of attack. The disease, 
however, would no doubt follow its host into any region unless 
rigid quarantine measures were taken against its introduction. The 
conditions that prevail in Trinidad imply that the fungus may be- 
come of less importance the farther north the cultivation of Hevea 
is extended. 
ERADICATION 
Forestal and crop associates are to be considered, in that under 
the former is included the infected wild rubber in the vicinity of 
the estate. It has been pointed out by Bancroft that any attempt 
to eliminate wild rubber in the region of estates is impracticable 
both on account of the cost and the probable great distances from 
which spores may be carried by the wind. Local eradication of wild 
Hevea, however, would go a long way in reducing the amount of 
spore production in the vicinity of the plantation. Crop associates 
in many cases carry the ubiquitous Diplodia, promote the moisture 
content of the soil and air, and protect the fallen infected leaves 
from drying. 
The cutting out of all new shoots in order to reduce conidial 
infection on young leaves over a period of several weeks, as proposed 
by Stahel. is scarcely feasible over large estates. The fact that the 
leaves are frequently in all stages of development throughout the 
year makes such a procedure difficult. 
The elimination of infected leaves from estates would almost 
necessarily be a continuous process, owing to the irregularity of 
their development and the continuous production of spores from the 
wild trees. However, repeated cleaning of the estate, if it could be 
cheaply and efficiently done, would gradually reduce the spore pro- 
duction and lessen the degree of infection. 
