MOSAIC OF SUGAR CAXE AND OTHER GRASSES. 21 
produce diseased plants and that careless importation of seed is 
apt to result in increased amounts of the disease. 
In the Hawaiian Islands also the disease is controlled by selection 
of clean seed and the use of resistant varieties. 
Measures for controlling the mosaic disease recommended in the 
following pages are not haphazard expedients, but have been used 
with very satisfactory results in Porto Rico for more than a year. 
Planters there have paid a heavy price to learn them, and it is urged 
that planters of sugar cane in the United States cooperate to prevent 
a possible epidemic. Indifference to the situation may result in the 
cane growers being confronted with the fact that it is too late to prac- 
tice seed selection, as is already the case in western Porto Rico. 
At present, it will work no particular hardship on the planters to 
take steps that will reduce the disease to a minimum. 
ELIMINATION BY ROGUING. 
Roguing consists of pulling out infected plants, root, stem, and 
branch, and throwing them down between the rows. It is based on 
the fact that as soon as the plants are wilted they are no longer 
dangerous as a source of infection. This method is applicable only 
to fields in which the disease has not obtained a strong foothold. 
It is not recommended for fields in which the number of infected plants 
exceeds 5 per cent in half -grown to mature cane or 20 per cent in young 
plants just sprouting. The size of the field and the condition of 
surrounding fields with reference to the occurrence of the disease 
in them must also be taken into consideration. When the field is 
quite small or consists merely of a few rows or plants of a new variety 
being propagated for trial on a plantation scale, it should be rogued 
even if 100 per cent of the plants are infected. Such plants are a 
constant menace to plants in surrounding fields. In large fields 
where the proportion of diseased individuals is greater than 20 per 
cent, roguing is impracticable, not because the plants are any less 
potent as sources of infection, but because diseased plants produce 
mill able cane, and to destroy considerable quantities of such plants 
would probably result in greater financial loss than would be sustained 
by the reduction in yield due to new cases. Large fields with a high 
percentage of diseased plants should be allowed to mature, but no 
cane from such fields should be saved for seed. 
It is suggested that the following schedule of inspections and 
roguing be put into operation: In the spring, just as soon as all of the 
plants have sprouted, the fields should be inspected by passing up 
and down the rows. All diseased stools should be pulled out of the 
ground and cast down between the rows. If this first inspection is 
carried out in a thorough manner the field will be completely freed 
from the disease provided no secondary infections are going on. 
