3) FOLIAGE DISEASES OF DURIAN
3.1 DURIAN LEAF BLIGHT
This disease are caused by fungi namely Rhizotonia solani on both foliage of seedling and adult durian tree. The disease started with a small water soaked spots on the leaves and than become larger in size. The lesions than dry-up and become light brown and darker and later curly. The affected leaves twigs appear shriveled, dedicated and necrotic. Some mycelial threads of the fungus appeared on the diseased leave. The damaged leaf reduces the photosynthesis process and less flower initiation at certain critical period. Many tiny , light brown sclerotic patches frequently appear and infected leaves easily fall at serious stage. Less leaves means less photosynthesis process which give negative impact to the flowering and fruiting process. This disease controlled at seedling stage by less reducing excessive watering activity and by spacing the seedling plants in the nursery. Spraying of fungicide are the practical control measure with Benomyl, Carbendazim, Triadimefen and many others. There are practical method by injection the fungicide into the trunk of matured tree.
3.2 DURIAN LEAF SPOT
This disease caused by a type of fungus namely Phomopsis durionis. The premature leaves tend to abort prematurely when attacked by this disease. Seedling stage are easily attacked by this disease. When there is defoliated, the shoot are easily sunburn and secondary infection with Lasiplodia theobromae fungus occurred. However from my observation, there is no severe attack of this disease for mature durian tree. If any attack occurred the early sign are tiny spots with yellow than turn brown look like necrotic. On the reverse side of the leaf, the spots are difficult to see as they are masked with peltate leaf scales. Very little scientist known about this epidemiology, there may be an association of damage by insects and fungal infection. The mature tree with lush foliage and seedling stage can be controlled by spraying of systemic fungicide such as benomyl, carbendazim and triophanate methyl as per label recommendations.
3.3 DURIAN LEAF ANTRACNOSE
Durian leaf Antracnose Disease are caused by Collectotricum gleosporoides which able to associate with meteorological nutritional and environmental factors. As I observed, this disease occurs on durian leaves as discrete, round, necrotic leaf spots and irregularly-shape necrotic patches usually near the margin of the leaf tip. The leaf spots are pale grayish-brown centers, with more or less concentric rings of tiny black spot or dark brown. The recommended method to control the antracnose disease in the nursery is to apply foliar sprays. Spraying of fungicide such as benomyl, thiophanate methyl or carbendazem wih combination of chlorothalonil, propineb, menthiram, mencozeb and maneb will be suitable.
3.4 DURIAN LEAF GREEN ALGA RUST
The disease are caused by green alga known as Cephaleuros virencen which causes spots on durian leafs. It reduces leaves photosynthesis activity and vary easy to control. This disease occurred due to the environmental stresses such as poor soil conditions, thick undergrowth, overcrowding and attack by the insects of mites infestation. Sign of the disease are rust-colored velutinous spots vary from 3-5 mm in diameter and usually found on the upper surface of the leaves. The infestation may cause the bark on twig to crack which open for the secondary infections by other microorganism. Alga rusts infection may serious when the durian tree are unhealthy. From my observation, the best way to control this problem is to revitalize the tree properly by fertilizing and irrigating. Other method is by alleviating the nutritional deficiencies, reducing humidity around the tree and increasing the air circulations in the canopy. For stubborn infection, spraying of fungicide are practical with fungicide such as fentin acetate, benomyl, thiram or copper fungicide.
All the four foliar disease above are easy to identify if we familiar with the symptoms. Most matured healthy durian tree are not seriously attacked by this foliar disaeae with adequate agronomic practices. I hope this article provide additional information for all "Anim Agro Technology" readers a fruitful knowledge. Thanks.
|Matured durian fruits at Muar, Johor.|
(3 January 2013)