Economically Important Leaf Diseases of Rubber

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

http://www.malithiweerakkody.com/

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

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



Raised blisters on a rubber leaf

infected by Colletotrichum leaf disease.

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)



White powdery spots on a rubber leaf

infected by Oidium leaf disease.

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)


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 15oC

to 40oC. 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)


Railway-track lesions on a rubber leaf

infected by Corynespora leaf disease.


Image and Information Source:

Rubber Research Institute of Sri Lanka http://www.rrisl.lk/

Prepared By: Malithi Weerakkody | www.malithiweerakkody.com

http://www.malithiweerakkody.com/

Economically Important Leaf Diseases of Rubber

Environment

Transcript of Economically Important Leaf Diseases of Rubber