Desiantha weevils and rutherglen bugs are in canola
Farmer John Parsons has found desiantha weevils (also known as spotted vegetable weevils) and rutherglen bugs in his Bonito canola crop near Wandering. The canola plants ranged in growth stage from cotyledons to the four leaf stage. The older canola plants had visible feeding damage but new cotyledons were not damaged. The farmer was monitoring the crop to decide if insecticide needed to be sprayed.
Desiantha weevil adults are mottled grey-black in colour with grey flecks on the abdomen and have the typical elongated weevil snout. They grow up to 7mm long and are flightless. Larvae are white, legless grubs with orange-brown heads and grow to 8mm in length.
Desiantha weevil larvae attack cereals at the seedling and tillering stages. They feed underground on germinating seeds, and bore into the stems of seedlings and tillers, often killing plants or resulting in abnormal and stunted growth. In contrast, canola is mostly damaged by adults. They chew cotyledons, leaves and stems of canola plants and may eat small plants down to ground level.
Rutherglen bug adults are 4mm long, have clear wings folded flat on the back, are grey-brown-black in colour and are very mobile. Rutherglen nymphs have a pear-shaped, red-brown body. Swarms of the bugs, nymphs and adults, often move out from under weed plants when they are disturbed. Damage from the rutherglen bugs is similar to mite sucking in that seedlings will become stunted, discoloured and distorted. Rutherglen bugs do most damage to moisture stressed plants.
Rutherglen bugs prefer warm dry conditions and should become inactive and die out with prolonged cold and wet winter weather patterns.