LEAF DISEASE OF PARA RUBBER 9 
DESCRIPTION OF THE DISEASE 
The leaf disease appears first on the tender, pendent, very 
young (3 to 5 days old) leaves as opaque olive-green spots, 1 to 5 
centimeters in diameter, on the naturally translucent reddish 
brown surfaces of the leaflets. When many spots develop the 
leaflets soon blacken, shrivel up, and fall oil', followed in a few 
days by the long naked petioles. (PI. III.) A severe general 
attack at this stage gives much the same impression as a case of 
Phytophthora leaf fall, except, of course, that it is confined to 
the very young leaves. Since, following the annual "wintering" 
period, the trees put out new leaves over the entire crown or at 
least over entire branches at approximately the same time, it is 
clear how a severe attack of the disease at this crucial stage can 
cause complete defoliation. In the course of four to five weeks 
after the first defoliation the trees have again put out a new 
crop of leaves, which in turn may be killed and drop off. Thus, 
the planting appears to be continuously going through the winter- 
ing process. Stahel (23) found that three successive defoliations, 
occurring over a period of about six months, were sufficient to 
cause a general dying back of the entire crowns of 5 to 6 year old 
trees. This die-back, which is generally an indication of the pres- 
ence of the leaf disease in a planting, was shown to be due to local 
starvation resulting from depletion of the starch reserves, first in 
the smaller branches and finally, with repeated defoliation, in the 
larger limbs and even in the trunk itself. Reduction in the yield 
of rubber follows closely the exhaustion of reserve food materials, 
so that after a few defoliations tapping becomes unprofitable. 
Less severe attacks of the disease usually cause only the shedding 
of occasional leaflets, which, combined with more or less stunting 
of the remainder, gives the foliage a peculiar thin appearance. 
When only a few spots develop on a very young leaf the unaffected 
portions continue to grow and cause a characteristic* crumpled ap- 
pearance. (PI. Ill, fig. 1.) The subsequent falling out of the dis- 
eased portions, especially of the marginal ones, on such leaves gives 
them a ragged shot-hole aspect, which persists until the following 
wintering period. (Pis. IV and V.) This frayed-out condition is 
typical of a mild attack, and where not many of the leaflets actually 
drop off it has apparently little or no effect on the yield of latex. 
Naturally all degrees in severity of attack may be observed, but 
the symptoms above described develop especially when infection 
occurs on very young leaves, 1 to 3 days old. According to 
Stahel (23) ^ leaves more than a week old rarely become infected at 
all. Even before this the tissues have already become firm and more 
resistant to penetration by the fungus, so that the resulting lesions 
are quickly delimited, often somewhat hypertrophied, and usually 
small (1 to 4 millimeters in diameter), with sometimes a dead papery 
center. (Pis. IV and VI.) Although large numbers of these minute 
spots may develop on a single leaflet and cause considerable stunting, 
death rarely results. 
The under surface of both large and small spots has at first, under 
moist weather conditions, a velvety grayish white appearance from 
the millions of spores (conidia) of the fungus produced on slender 
conidiophores arising from the diseased leaf tissues. Later, over the 
106650°— 24 2 
