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Mandalotus weevil

Mandalotus weevils (Mandalotus spp.) have been identified for customer service manager, John Ellis (AGnVET Services). The weevils have caused extensive damage to a monola crop near Henty, in the South West Slopes district of New South Wales. Very high numbers of weevils were found across the paddock and entire areas have been completely bared out. John says the paddock will need to be re-sown due to the extent of damage. In 2009, this paddock was sown to oats. Mandalotus weevils have also been recently identified in samples from a lupin paddock near Lake Bolac, in the Western district of Victoria, and a canola paddock near Young, in the South West Slopes district of New South Wales.

Adult Mandalotus weevils are 3-5 mm in length 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. Click here for images of Mandalotus weevils.

Little is known about the biology of Mandalotus weevils. They were first recognised as a significant pest in 2003 in the Mallee district of South Australia. 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. Since 2006, we have been received reports from the Riverina, South West Slopes and the Southern Tablelands districts of New South Wales, and the Wimmera and Mallee districts of Victoria. In most cases, weevils have been found attacking emerging canola crops.

There are currently no chemicals registered for controlling Mandalotus weevils, however growers have reported some success using high rates of bifenthrin or chlorpyrifos. We have also had reports that indicate crops sown with fipronil-treated seed may suffer less feeding damage than other crops. Remember that healthy plants may be able outgrow damage caused by weevils.

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