Corynespora attacks my Rubber trees

Every year the rubber trees shed their leaves to regenerate between the end of December and mid February. During regeneration it is common for the tender leaves and shoots to be affected by a disease known as Powdery Mildew caused by Oidium heveae Stien subjecting it to gnarling. To prevent the attack of Oidium, dusting of sulphur during refoliation period commencing from bud break is done at fortnightly interval.



Healthy Foliage (click on the picture to enlarge)

Generally sulphur is dusted in the tapping mature areas only because the incidence of leaf fall is more in tapping trees of age 7 years and above. This year, as a precaution I also dusted my 6 year old 2004 replanted area which is to be opened for tapping in 2011. After about 10 days of the second round my supervisor called me to say that there was abnormal drying of leaves. I assumed it to be due to the extreme hot weather conditions. Since I stay close to the Rubber Research Institute of India I dropped into their Pathology department and explained the symptoms. They too regarded it has drought induced drying.



Corynespora affected foliage (click on the picture to enlarge)

A week later when I visited the estate I was taken aback by the intensity of the leaf fall and figured that the patches followed a distinct path, that through which the duster was carried. I reckoned that it must be due to excess sulphur dusting on the immature young trees. I collected some sample leaves and took it to RRII. Unfortunately the Dy. Director was out of station and so had to leave the specimen there and come off. Promptly the next day I got a call from the Dy. Director who asked me to explain the occurrence. Both of us initially concluded that due to the young age of the trees and excessive use of sulphur it could be chemical toxicity and that there was nothing much to do about it. But he offered to visit the estate if I insisted. I asked him to make a visit and offered transportation.

Affected shoots

The next day morning we reached the estate which is 60 kms from Kottyam on NH220 towards Kumily. After taking a good look he identified it to be the leaf disease known as Corynespora Cassiicola or Leaf spot. I had heard of the disease before and was under the impression that it affects only the nursery plants. With 3 generations and 75 years of experience in rubber planting it was the first time that the disease was seen in any of our estates. So it came as a rude shock. It is also worthwhile to note that so far it is the first reporting of the disease from the Meenachil – Kanjirappally belt, the heartland of rubber growing tract of Kerala.

Affected leaves

Corynespora leaf disease formerly affected only the plants in the nursery. But now it has started attacking the mature trees as well. A few years ago Corynespora appeared in South Canara in Karnataka and now it has started appearing in many places in Kerala. The terrible nature of the disease can be gauged from the fact that the entire rubber area in Ceylon which was planted with RRIC 103 which was highly susceptible to Corynespora was cut and removed because of this disease. And it is a nightmare that our own RRII 105 is similarly susceptible!

Conditions for Development

Extended periods of rainfall and warm temperatures favor disease development. The fungus survives in crop debris or on weeds and other crops. It has a very wide host range. Spores are moved by wind and rain splash.

Control
Now I have to keep watch for the leafs to regenerate and as soon as they are tender green spray Copper Oxy Chloride mixed in rubber spray oil. And hope for the best. Since it has been identified positively, during subsequent years too I have to be careful and give an additional COC spray during regeneration of leaves after defoliation apart from the usual prophylactic spraying done before the onset of the monsoon rains.

Terrible day
To make matters worse, I lost my car keys while walking through the affected areas of the estate and couldn’t find it . A taxi was summoned from the nearby town Mundakayam . The taxi brought us back to Kottayam and after leaving the Dy. Director at RRII, I returned in the same taxi to the estate with the spare key to bring the car back home.

For more information on corynespora disease in rubber trees go to :- http://clinic.rubberboard.org.in/images/Researcharticles.pdf