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| Ash WhiteflyAsh whitefly is a pest that breeds on several tree species, in particular large ornamental trees. Those most at risk include various speices ash. Hawthorn, privet, crepe myrtle, tulip tree, star magnolia, medlar, phillyrea, photinia, firethorn, buckthorn, lilac and crown of thorns also may be infested.
Some fruit trees are minor hosts, the one most at risk being pomegranate. The experience in South Australia is that ash whitefly does not become a serious pest of pome fruit and only rarely occurs on olives.
Ash whitefly attacks the leaves and not the fruit, so it does not cause the fruit to become inedible or unsaleable. Essentially, it sucks the sap and this can stress the tree as well as causing sooty mould to grow on foliage below feeding sites. It is not a quarantine issue on export fruit. It has been present on the mainland since 1998 and occurs in many countries.
There is no evidence that ash whitefly transmits diseases.
In the adult stage, ash whitefly looks very much like the common greenhouse whitefly – white-winged insects 1.5 mm long and found typically on the underside of leaves - but occurs on a range of host plants not usually attacked by greenhouse whitefly. The juveniles are oval, scale-like forms about 1 mm long also under leaves.
They are distinguished from the relatively featureless common greenhouse whitefly by white waxy tufts on their backs. Another useful way of distinguishing the ash whitefly from the common greenhouse whitefly is by identifying the plant hosts. For example, ash whitefly do not infest tomatoes, pumpkins or potted, ornamental annuals.
It is only with heavy infestations that there is premature leaf drop or undersized fruit. For winter they leave deciduous host trees and move to photinia and citrus foliage where they are frequently washed away by rain.
Ash whitefly is typically
about 1.5 mm long | 
Ash whitefly attacks the
underside of leaves | 
Ash whitefly pupae
in close up |
In most cases, ash whitefly will be suppressed by its natural enemies if you do not use harsh pesticides to treat other pests. This is usually the best option.
For smaller ornamental trees, a generic whitefly foliar pesticide is the second best option. These include horticultural oils and soaps that are relatively safe to handle although not entirely safe to beneficial insects.
For larger ornamental trees, spraying is difficult, so soil injection of systemic insecticide, as is done in Melbourne and Adelaide, may be an option but this may require a special permit from the Australian Pesticides and Veterinary Medicines Authority.
More information on ash whitefly is available from the SARDI website.
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