COFFEE LEAF SPOT IN PORTO RICO. ■ 11 
RECOMMENDATIONS FOR CONTROLLING STIBELLA. 
The- degree of control which was maintained over this disease under 
very adverse circumstances demonstrated that it could be handled 
easily by destroying the host plants and after that by maintaining a 
quarantine. 
If Stilbella is to be controlled on an infected area the work will 
be simplified by first establishing clean cultivation. This can be done 
by weeding the area frequently. There should be little or no diffi- 
culty in keeping weeded a section that is heavily shaded by the coffee 
and shade trees. After the grass and weeds have been killed, the 
coffee trees should be cut away 6 inches above ground and the stump 
left with a clean diagonal cut which will shed the rain. This should 
be done as soon as the crop has been removed, so that full advantage 
can be taken of the dry season. The felled trees may be chopped up 
just where they fall. The control of the disease depends on the thor- 
oughness with which the host plants are destroyed. Any careless 
overlooking of diseased plants may mean speedy reinfection of the 
coffee. Subsequent work consists in keeping the coffee and adjacent 
areas free from weeds which may harbor the disease, and also in 
maintaining a sharp lookout for reinfection in order to remove any 
disease as soon as it appears. 
In vicinities where conditions are favorable to Stilbella, coffee trees 
that have long been severely affected would be greatly improved were 
they cut to a low stump and forced to develop a new trunk. In the 
experiment discussed in this bulletin two entire crops, most of a third, 
and possibly part of a fourth crop were lost through felling the 
coffee trees. If maintained free from disease the new growth should 
soon yield more than enough to compensate for this loss of crop from 
the old diseased trees. 
Good results are much more certain to follow where all Stilbella- 
infected sections of a plantation are cleared in the same season than 
where some sections are left to be worked over later. On many plan- 
tations this can be done. Where, for economic reasons, it is imprac- 
ticable to work over the whole diseased area in one season, the most 
isolated and the most elevated sections affected should be cleaned first 
in order to leave no diseased tracts overhanging the cleaned ones. All 
natural barriers, such as ridges, uninfected plantings of food crops, 
or pasture land, should be taken advantage of; and where no natural 
barriers exist, a strip of coffee may be destroyed along the edge of the 
section to be cleaned and rows of bananas planted closely enough to 
offer a barrier against the diseased plants outside. Care should be 
exercised to reduce to a minimum the passing of pickers and laborers 
from diseased into disease-free sections. 
