New citrus pest discovered in the Western Cape

Two researchers, one of them a research fellow at the Department of Botany and  Zoology at Stellenbosch University, were the first to recognise a plague affecting plants in the Western Cape and has recently submitted their findings for publication in a scientific journal.

Prof Jan Giliomee, with the assistance of Mr Ian Millar of the South African National Collection of Insects in Pretoria, determined that the white woolliness detected at the bottom of lemon leaves in gardens in the Western Cape is the woolly white fly, <i>Aleurothixus floccosus</i>.

“The nearest place to South Africa where this pest has previously been observed, was Angola, but now it is everywhere in home gardens of the Cape Peninsula, the northern suburbs and in Stellenbosch, but fortunately not yet in commercial citrus plantations. It is not known how it reached  South Africa, but someone must have brought infested plant material into the country”, Prof Giliomee said.

This whitefly was noticed for the first time in Jamaica in 1896. In 1966 it spread to California and later to many countries of the world, where  it is sometimes considered a serious citrus pest.

“ Despite its name it is not a fly, but a small moth-like, sucking insect, related to aphids and scale insects. It is also closely related to the white flies which occur commonly on beans and tomatoes in home gardens. The immature stages are attached to the plant with their sucking mouthparts and, while sucking the plant juices, secrete a white woolly substance and drops of honeydew. The sweet honeydew attracts ants and later a black fungus, called sooty mould, will grow on the honeydew, giving the leaves a black appearance. The adults are small flying insects which also suck plant juices”.

According to Prof Giliomee it does not look as if light infestations do much damage to the trees and they can be sprayed off with a garden hose or the infested leaves can be picked  and destroyed. Heavy infeastations might need more drastic measures with insecticides.

 “Plants that are not treated can lose their leaves and the harvest may be affected. However, the fruit are not affected by the insects and those of infesteted trees can still be consumed”.

Prof Giliomee added that if the woolly whitefly should move to commercial citrus orchards it may affect the crop. “This would no doubt require treatment on a larger scale”.

• Contact prof Jan Giliomee at tel. 021 808 2718 or by email at jhg@sun.ac.za for more information.