Plant Health


The Pacific’s fragile ecosystem is constantly at risk from invasive species, pests and diseases. It is therefore vital that sustainable and appropriate management practices are developed and utilized to ensure   sustained productive use of the land. Plant Health aims to promote these practices by utilizing its three main units, entomology, pathology and weeds in undertaking regular surveys of pests and diseases, providing information, creating awareness among farmers,  updating information databases and assisting in eradication activities. 
 

Spiraling whitefly SWF (Aleurodicus dispersus)
Wednesday, 19 May 2010 08:54

Whiteflies are more important as vectors of many virus diseases than as direct pests.  Heavy infestations will reduce plant vigour. The pest is more important as a transmitter of viruses such as sweet potato mild mottle virus, sweet potato yellow dwarf disease, sweet potato leaf curl, and particularly sweet potato chlorotic stunt virus, a key component of sweet potato virus disease.

Host range

It is present in most of the sub-tropical and tropical conditions.SWF is present in most of our economically important crops such as cassava, chili, guava, sweet potato, banana, avocado cabbage, capsicum, cassava, cauliflower, citrus, coconut, cotton,  eggplant, garlic, guava, legumes, mango, mustard, onion, pepper, radish, squash, soybean, tomato, and tobacco. SWF is also present in woody plants such as ornamentals.

Damage symptoms

Both immature and adult whiteflies feed by piercing the undersurface of leaves and sucking the plant sap.  Whiteflies produce honeydew, a sugary secretion, making the leaf surface sticky.  In humid conditions, sooty mould may develop on the leaf surface, reducing its capacity to trap light required for the plant's normal growth.  The nymphs, which feed in one position for 2-4 weeks, may cause yellow spots which are conspicuous on the upper leaf surface.  Feeding by adults usually causes no visible lesion, but high whitefly populations may cause yellowing of infested leaves, and may stunt plant growth.

Ecology

Eggs are laid on leaf surface, usually on undersurface, in irregular, waxy lines, forming a spiral ( hence the common name). Eggs take about seven days to hatch. There are four larval stages that takes about 30 days. Only the first instar larva is mobile while the other three instars  are not. The final instar, the pupa, colorless or yellowish oval shape is about 1mm in length. They secrete waxy threads on their back which are about 12-15 mm long and provide a protective cover. The adults are white and quite small, about 2-3 mm  in length and coated with a fine dust-like waxy secretion. The eyes are dark reddish-brown, wings are transparent with white powder covering it. Females lay eggs throughout their lifetime

Management

Cultural control

Field sanitation and use of insect-free planting material.

Biological control

Natural enemies were such Nephaspis bicolor and Nephaspis oculata are recommended.

 

http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/economic-impact/aleurodicus-dispersus/index.html


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Effective management can help maintain productivity of land resources,stregthen food security, safeguard the environment and increase revenue. Plant Health strives to improve awareness on environmental implications of agricultural practices and offering safer environmentally friendly options.