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Small lucerne weevil

Consultant, Glenn Shepherd (IMAG Consulting), has found weevils attacking an emerging wheat crop near Orange, in the Central Tablelands of New South Wales. They have been identified by Judy Bellati (SARDI) as the small lucerne weevil (Atrichonotus taeniatulus). This weevil is known to attack lucerne, pasture legumes, canola and some weeds. They are not regarded as a pest of cereals, and in New South Wales, the small lucerne weevil is a minor, irregular pest.

Adult weevils are grey in colour with some brownish mottling, and are up to 10 mm long. During the day, they typically hide in the soil around the base of plants, though some may be found resting together in groups of 3-4 on a single leaf. The larvae are creamy white, legless grubs, up to 8 mm long, with small, pointed, brown jaws. Click here for images of the small lucerne weevil.

Infestations of small lucerne weevils spread slowly because they do not fly; they have to walk or be carried to spread. Young larvae become active in spring and feed on plant roots until mid-January. Adults emerge from the soil from mid-February - March. Eggs are laid at the base of plants, and after hatching in winter, larvae burrow into the soil and begin feeding on roots. 

Large numbers of adults can cause serious damage to subterranean clover pastures by chewing off cotyledons soon after germination. However, they are most damaging to lucerne. Adults feeding on leaves can defoliate plants. The most serious damage occurs when larvae burrow into or chew furrows in the taproot. Eventually plants die, resulting in lucerne stands with dead patches that increase in size each year as the infestation spreads. Wilting and plant death is most noticeable in summer when larvae are nearly full-grown.

Glenn reports that the damage is rather patchy within the paddock, which contains some clovers and Patterson’s curse. Adult weevils may have survived on these host plants over the autumn months, and have only recently moved onto wheat seedlings in search of food. The paddock is likely to have contained small lucerne weevils last year when it was sown to canola.

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