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Mandalotus weevil

Grower, Rob Taylor, has experienced Mandalotus weevils (Mandalotus spp.) damaging emerging canola crops at Grenfell, in the Central Tablelands of New South Wales. Rob says the weevils have been causing problems for several years across his farm, particularly on lighter soil types. Mandalotus weevils are a sporadic pest of canola, cereals and beans.

Little is known about the biology of this weevil. It is commonly found on rubbly sandy loam soil; hence it is often referred to as the ‘rubble bug’. The Mandalotus weevil was first recognised as a significant pest in 2003, where it caused severe damage to canola crops in the Mallee region. The distribution has likely widened in southern Australia in the past few years. It appears that the population increase of this weevil is a direct result of minimum tillage. The amount of trash in paddocks is also thought to create a more favourable habitat.

The adults are mostly active at night. During the day they can be found hiding under dirt and trash. In some cases numbers can exceed 500/m². Mandalotus weevil can be mistaken for sitona weevil, however it is more rounded in appearance, 3-5 mm long and dull brown in colour. Click here for images of Mandalotus weevils.

Usually, feeding damaged is 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. Rob reports the damage is patchy within the affected paddocks, with scallop-shaped pieces removed from emerging cotyledons.

Monitoring for Mandalotus weevils should be conducted at night. Adults are difficult to control with chemicals. Over the past few years a number of insecticides have been tried. In more recent times, growers in South Australia have had success with bifenthrin. Rob reports that crops sown with fipronil-treated seed suffered far less feeding damage than neighbouring crops that were sown with seed treated with imidacloprid.  

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