Washington Palm (Washingtonia robusta)
Zainab Ijaz, Dr. Imran-ul-Haq, Dr. Sajid Aleem Khan, Dr. Rashad Waseem Khan Qadri, Dr. Rana M. Sabir Tariq
The Washingtonia or Mexican Fan Palm is an ornamental tree which can be seen around 40 to 50 feets and sometimes can also reach the height of 80 feets. These plants are striking when planting in groups against high rise buildings. It is also considered as a desert palm because it is native to those areas having permanent subsurface water.
Their trunk is reddish brown which is 1 ft in diameter, swollen at the base that is ringed with leaf scars. The leaves are green in colour, glossy, rich, palmate and have filamentous fibers at the margins and they are present on the edge of orange leaf stem with saw tooth spines. Flowers are small creamy white present on the inflorescence. When flower matures they form black barriers. These plants are hermaphrodite and self pollinated with one plant.
Botanical Name: Washingtonia robusta
Common Names : Mexican Fan Palm, Mexican Washington Palm
Family: Arecacae (Palmae)
Native Origin: Northwestern Mexico
Hardy Range: 9A – 11
Mature Height: 60 – 80’
Mature Spread: 10 – 15’
Growth Rate: Moderate to fast
Their leaves are palmate fan leaflets and have petiole. Lower leaves when die form a dense shaggy covering below the leaves. Circular and blue-black fruit is present. This plant grows best in moderately rich and well drained soil but as well as it can also survive in poor soil condition. It is drought tolerant but when sufficient moisture is available it grows better.
Environment: Sandy loam, alkaline and acidic soil.
Exposure: Full exposure of sunlight is required for best growth of this plant, but partial shade is required when plant is young.
Economic Importance: It is the widely used tree present in the world & economically it is very important. It provides shade to humans. These trees are large fruit producers. Oil, biodiesel, wax, jelly and wine are produced from palms. Their leaves are used for making roofs. Their wood is used in furniture making.
Medicinal Value: Palm oil is used as antiseptic and regulates urinary disorders. It is beneficial for sore throat. Its oil is beneficial for scabies & toothache. It is used for malnutrition and weakness. It purifies blood and used in asthama.
Current developments for the management of Palm disease in Pakistan:
A HEC funded project titled “Etiology and integrated management of declining perennial ornamental plants” is being run by Dr Imran ul Haq in “Fungal Molecular Biology Laboratory, Department of Plant Pathology, and University of Agriculture Faisalabad. The project aims to identify the diseases of various ornamental plants including ‘Washington palm, lady palm, foxtail palm, wall palm, Alexandra palm and fishtail palm etc. Etiology and management of various other diseases is under consideration. No sooner, there will be complete profile of various ornamental plants diseases with their pathogens and management. This literature will be published in both English and Urdu, so as to help the farmers, gardeners and nursery growers to combat the emerging issues of ornamental plants.
- Diamond Scale Disease: This disease is caused by the fungus Phaeochoropsis neowasgingtoniae. It produces diamond shaped fruiting bodies on the foliage of tree. Maxican fan palm is the primary host of this disease. At the initial stages of the disease tiny, watery looking, dark spots appear and form diamond shaped. Leaves turn yellow than brown. Improve drainage and proper fertilizers are required to manage this disease.
- Fusarium Wilt: Fusarium oxysporum is responsible for the cause of this disease. Leaves in the lower part of the canopy turns brown and hanging to the plant. Discoloration of leafstalk may occur and black streaking appears on them. This disease kills the plant sooner or later and stresses the plant. The fungus can enter through the wounds. Disinfection of pruning tools may avoid the disease.
- Pink Rot: It can attack any part of the tree, however it is a secondary disease. Brown syrup like ooze produce on the trees. Stunted or deformed growth is occur. Visible pink spores are produced. Over water or under water should be avoided, and use of proper fertilizer needed to manage pink rot.
- Other types of rot: Collar, foot and crown rots are produced by the fungus This fungus attacks the roots and crown and cause discoloration of leaves. Wilting of plant starts. These infections may cause cankers on trunks and oozing saps. Different fungicides are recommended to manage these rots.
- Sudden Crown drop: This disease is caused by the fungus Thielaviopsis paradoxa. It suddenly falls of the palm tree. Rots produced inside of the trunk without showing any outward symptom. This disease can be managed by pruning of trees.
Insects & Pests:
- Palm Leaf beetle (Brontispa longissima): This was first found in Darwin and nearby areas in 1979.
- Red / Sago / Asian palm weevil (Rhynchophorus ferrugineus): This weevil was first recorded in Spain and then in France. They are rusty red colour and their adults are in large number. Their larva affect the trunk of the tree by making a hole therefore death of host plant may occur.
- Coconut mealybug, palm plait plant hopper & Variety of Scales infest this palm.
Conclusions: Washington Palm is the largest and important ornamental plant. It is grown commercially. However some pathogens and insects are attacking on it and cause diseases and kill them. It is necessary to save these palms by adopting IDM practices.