Blue-green aphid now widespread in N.Z.

Press, 20 April 1979, Page 9

Blue-green aphid now widespread in N.Z.

The blue-green lucerne aphid (Acyrthosiphon kondoi), now also known as the blue lucerne aphid, is a native of Manchuria and has also been recorded in Japan. U.S.A., and now New Zealand, and since its arrival in the far north of New Zealand in 1975 it has quickly become widespread throughout the country. Compared with other aphids, it is smallish in size with a waxy appearance; it clusters toward the top of the stem and in folded leaves in lucerne, and in the florets of flowering clover. There are winged and wingless forms. there often being a high proportion of winged forms on maturing crops. While the blue lucerne aphid has an obvious preference for lucerne it also attacks and is of economic importance in white and red clover seed crops, and some other small seeded legumes. As the aphid cool, damp, overcast conditions it is found in greatest numbers in the springearly summer, autumn and winter periods. There is no sexual phase of reproduction in the life cycle as all aphids are females and produce live young. While populations of

over 1200 per stem have been recorded in lucerne, five per stem are sufficient to cause a reduction -n

lucerne productivity over the slow growing autumn, winter and spring periods. losses are markedly enhanced when populations rise to 30 per stem or beyond. Work in the southern North Island has shown that a heavy infestation of young regrowth lucerne in the early autumn can result in an immediate 70 per cent production loss. In the absence of any later aphid infection, the autumn loss can extend into the winter and spring as a 50 per cent and 30 per cent herbage loss respectively, with 15 per cent plant deaths by spring.

The main symptoms of damage are a stunting of growth and regrowth, crimping and shortening of the internodes, leaf curling, wilting and yellow ing. The cause of damage is due to a reduction in plant sap and presence of a toxin injected into the plant by the aphid.

Ladybirds. lacewings and syrphid larvae are the commonly found predator of the aphid and. where sustained, will provide realistic complementary con-

trol to chemical or cultural measures However, for integrated control and to succeed the aphicide used must be selective to aphid predators.

Grazing, ensiling or haying of infested lucerne stands have all been shown to substantially reduce aphid populations, but should not be prac tised at the expense of proper stand management. In many such cases, there will be a likely need for treatment of subsequent regrowth with an aphicide Extensive trials and field evaluation of “Pirimor” 50 DG in New Zealand have shown rates of 250 grams of product per hectare to have provided from 87 to 100 per cent control of blue lucerne aphid. The product provided a rapid aphid knockdown. and populations remained at an acceptable level for up to six weeks following treatment. It is one of the few aphicides selective to ladybirds and other aphid predators and is relatively non-toxic to the operator. It acts on contact and also has a fumigant and translaminar effect, and will therefore kill aphids untouched by the spray solution.