Bronwyn Hunt (Merriwa Pastoral Company) has observed sitona weevil (Sitona discoideus) in the southeast corner of the Mallee within canola paddocks that were sown into barley, wheat and canola stubble. The weevils are attacking the cotyledons of medics, but not directly feeding on the canola seedlings. Based on previous years, Bronwyn says sitona weevil feeding damage can kill the plant or delay the emergence and size of medic leaves. Due to the current conditions of decreasing temperatures and added water stress, it may be difficult for medics to grow beyond the damage sustained.
John McCredden (North West Ag Services) says he has received a number of reports of sitona weevil causing damage to medics in the southern Mallee and northern Wimmera, although the numbers appear to be relatively low at this stage.
Sitona weevil larvae feed through winter into spring, after which they pupate in the soil and emerge as adults in late spring/early summer. Adults can fly considerable distances, so infestations can start without a previous history of damage. Larvae feed within or on the root nodules, while adults typically make scallop-shaped notches along leaf margins.
One control option is to use a chemical application aimed at the sitona weevil, lucerne flea and earth mites. However, sitona larvae are protected in the soil and difficult to kill. Adults can be controlled with chemicals, but the economic returns of spraying are questionable.