This informative booklet provides a basic knowledge of economically important rubber leaf diseases in Sri Lanka. Information and image source: Rubber Research Institute of Sri Lanka

1. Disease Causative Agent
Colletotrichum Leaf Disease
Colletotrichum acutatum
C. gloeosporoides
Powdery Mildew Oidium heveae
Phytophthora Leaf Fall
(Abnormal Leaf Fall )
Phytophthora spp.
Bird’s Eye Spot Disease Drechslera heveae
Corynespora Leaf Fall
Disease
Corynespora cassiicola
Economically
Important
Rubber Leaf
Diseases
Image Credit: Rubber Research Institute of Sri Lanka
Prepared By: Malithi Weerakkody

2. Various diseases affect rubber cultivations all over the world. These disease may result in
growth retardation, extensive defoliation, loss of latex yield and death of affected trees.
However, the exact economic threat of each disease varies from one country to another,
according to the climate, cultural practices, and the types of clones cultivated.
In Sri Lanka, almost all economically significant rubber diseases are caused by fungi. These
diseases are categorized according to the part of the plant affected; leaf diseases, stem/branch
diseases, panel diseases, and root diseases.
The most common leaf diseases affecting the rubber plantation in Sri Lanka are discussed in
this report.
INTRODUCTION
Source: Rubber Research Institute of Sri Lanka

3. Causative agent: Colletotrichum acutatum & C. gloeosporoides
Colletotrichum leaf disease occurs throughout the year and spreads severely during the Southwest and
Northeast monsoon season. Colletotrichum spp. produce great numbers of spores, which are
spread by rain splash and damp air currents. The pathogen penetrates directly through the cuti-
cle, destroying the cell wall in the process. Infection occurs when the humidity exceeds 96%.
Symptoms:
Young leaves are the most susceptible. Copper-brown leaves usually discolor, shrivel and fall off.
Apple-green leaves show tip die-back. Older leaves are resistant to infection and show only partial
damage or are extensively spotted. The spots are circular with a narrow brown margin surround-
ed by a distinct yellow halo. When the leaves mature, such spots appear as raised blisters. Severe
infection could kill the shoot up to the bud patch during prolonged wet weather in budded
stumps.
Severe attacks in nurseries can result in leafless trees, growth retardation and budding difficulties
due to bark changes. On mature trees, production levels are affected and trees suffer die-back.
Colletotrichum Leaf Disease
Source: Rubber Research Institute of Sri Lanka

4. Image Credit: Rubber Research Institute of Sri Lanka
Raised blisters on a rubber leaf
infected by Colletotrichum leaf disease.

5. Causative agent: Oidium heveae
Powdery mildew is the most widespread cause of the diseased condition of rubber known as
secondary leaf fall (SLF). It is most pronounced during the refoliation period (February-March).
The fungus survives in nurseries, self-sown seedlings, and in immature leaves of the shaded
canopy. The transmission is through air-dispersed conidia.
Symptoms
This disease causes defoliation of young shoots; and discoloration and curling from the mar-
gins on older leaves. The susceptible clones result in poor canopies due to secondary leaf fall.
Rubber leaflets infected by O. heveae at the Copper-brown stages become shriveled, necrotic
and later fall off.
The mildew colonies appear as white powdery spots on both leaf surfaces and are most
noticeable on the lower surface. A severe attack of SLF is shown by a pale green carpet of
leaves, which is seen on approaching the trees. Repeated defoliation leads to dieback.
Oidium leaf disease (Powdery Mildew)
Source: Rubber Research Institute of Sri Lanka

6. Image Credit: Rubber Research Institute of Sri Lanka
White powdery spots on a rubber leaf
infected by Oidium leaf disease.

7. Causative agent: Phytopthora meadii / P. palmivora
Phytopthora leaf fall disease occurs during the Southwest monsoon season and it is caused by the
same fungus that cause pod rot, stem dieback, bark rot or black stripe and canker. The dis-
ease is spread mainly by splash dispersal, currents of damp air and insects. The fungus has a
wide host range.
Symptoms
The disease starts on the pod, appearing as water-soaked lesions with black globules of latex.
In mature leaves, petioles show chocolate-brown to dark brown lesions with drops of coagu-
lated latex. Infected leaves are shed and the leaflets can be easily shaken off.
Severe infection leads to complete defoliation. In such event unlike in Oidium leaf disease,
new leaves will not develop until the next refoliation season. Growth and yield can be
seriously affected.
Phytopthora leaf fall (abnormal leaf fall)
Source: Rubber Research Institute of Sri Lanka

8. Causative agent: Corynespora cassiicola
The Corynespora Leaf Fall Disease is one of the most serious leaf diseases of rubber.
The disease was recognized for the first time in Sri Lanka during the year 1985 and so far,
more than 70 alternative hosts have been identified.
The disease spreads through windborne spores and they have the ability to survive up to 9
months in defoliated leaves on soil. Spores can germinate in temperatures ranging from 15o
C
to 40o
C. High humidity favors the spread of the disease.
Symptoms
Immature copper-brown and semi-mature apple green leaves are highly susceptible to this
disease. If the climatic conditions are favorable, the disease spreads causing leaf fall. Severe
and repeated defoliation could lead to dieback of stem and branches and some times could
kill the entire tree.
Characteristic symptom of this disease is the railway track appearance due to the blackening
of veins. However, deviations from the typical symptom have been identified on some clones.
Corynespora Leaf Fall Disease (CLFD)
Source: Rubber Research Institute of Sri Lanka

9. Railway-track lesions on a rubber leaf
infected by Corynespora leaf disease.
Image Credit: Rubber Research Institute of Sri Lanka

10. Image and Information Source:
Rubber Research Institute of Sri Lanka
http://www.rrisl.lk/
Prepared By: Malithi Weerakkody | www.malithiweerakkody.com