Mandalotus weevils

Mandalotus weevils (Mandalotus spp.) have been identified by senior technical officer, Ken Henry (SARDI), from a canola crop near Rupanyup in the Wimmera district of Victoria. The weevils were detected by agronomist, Adrian Tyler (Tyler’s Hardware & Rural Supplies), who found them chewing on canola plants that were lying on the ground. Adrian estimates that about one third of a 40 ha paddock was affected, and several hectares of this were completely bare. Re-sowing the worst affected areas is being considered, despite the patchy nature of the infestation.

Mandalotus weevils have also been identified for agronomist, Rick Rundell-Gordon (Dodgshun Medlin), who reports finding them in several canola crops around Sea Lake, in the Mallee district of Victoria. Rick says numbers were variable across the affected paddocks, with one particular paddock almost completely wiped out. Both Adrian and Rick reported that the affected paddocks were either rubbly or lighter, calcareous soil types, which are known to be favoured by Mandalotus weevils.

Adult Mandalotus weevils are 3-5 mm long and have a rounded, dull brown coloured body, which can easily be mistaken for a small clod of dirt. They are known to attack canola, cereals, beans and medic pastures. Adults actively feed during the night, whilst during the day they can be found hiding under clods of dirt and trash. Feeding damage is usually first noticed on the leaves of emerging crop plants. In severe cases the seedlings are often ‘ring barked’ just above ground level. This causes the plants to fall to the ground where the weevils continue feeding on the leaves.

Little is known about the biology of Mandalotus weevils so your observations and information are extremely valuable. The distribution and host range of Mandalotus weevils appear to have expanded in southern Australia in the past few years and population increases are probably the result of minimum tillage and stubble retention, which create a more favourable habitat. There are currently no chemicals registered for controlling Mandalotus weevils, however some growers have reported some success using high rates of bifenthrin or chlorpyrifos. Remember that healthy plants may be able outgrow damage caused by weevils.

Click here for images of Mandalotus weevils.