Weevils

There are several weevils that attack canola at establishment, and many of these will now be active.

Where have they been reported?

Several weevil species that attack canola will now be active. Correct identification is important, but quite challenging. Weevils, probably Fuller’s rose weevils have been reported damaging pasture seed crops near Orange in the Central Tablelands district, and near Scone in the Hunter district of NSW. Weevils that also appear to be fuller’s rose weevils have been causing some damage to several post-emergent canola crops northeast of Temora in the Central West Slopes & Plains district of NSW. The weevils have severed stems and damaged cotyledons, although the extent of the feeding damage is restricted. These paddocks were previously in pasture/lucerne fallows.

Whitefringed weevils (Naupactus leucoloma) were reported in late April in canola from the Big Springs area of the Riverina district of NSW. Mandalotus weevils (Mandalotus spp.) have also been reported near Nhill in the Victorian Wimmera. A full article on Mandalotus weevils will appear in the next issue of PestFacts SA newsletter.

Fullers rose weevil habits and behaviour

Fuller’s rose weevil (Asynonychus cervinus) attacks a wide range of broadleaf plants and occasionally damages canola, lucerne and pastures. They are more regularly a problem in commercial and ornamental horticultural crops. Damage can occur as adults chew stems, cotyledons and leaves of emerging crops; in canola and lucerne, damage can occur as serrated leaf margins. The flightless adults generally emerge from pupation sites in the soil between February and May, but can be present throughout the year. They have 1-2 generations per year.

Our advice

Fuller’s rose weevil is unlikely to cause significant damage to most crops; however monitoring is recommended. Because the adults are flightless, movement between paddocks is quite restricted, so there is merit in controlling damaging populations in spring prior to the following season.

Description

Adults are 8mm long, wingless with a short broad snout. They are grey-brown, darker on the sides with a distinguishing short, oblique, white line halfway along the body. They are flightless and have a habit of climbing. This species can be confused with the small lucerne weevil. Mature larvae are legless, yellow and about 6 mm long. For more information download the GRDC Back Pocket Guide - Crop Weevils, or for excellent diagnostic photos click here.

 

* Sources of field reports of weevils

Emma Robinson – Agronomist, Landmark (NSW Central West Slopes and Plains)

Frank McRae – Seed representative, AustWest Seeds (NSW Central Tablelands)

Chris Minehan - Agronomist, Rural Management Strategies (NSW Riverina)

Adam Pearce – Agronomist, Clovercrest Consulting (Victorian Wimmera)