Mites
Brown Wheat Mite
Blue oat mite is an important pest of seedling winter cereals, but generally restricted to cooler regions. If pale-green or greyish irregular patches appear in the crop, check for the presence of blue oat mite at the leaf base.
Adults are 1 mm long and have 8 legs. Adults and nymphs have a purplish-blue, rounded body with red legs. They move quickly when disturbed. The presence of a small red area on the back distinguishes it from the red egged earth mite.
Brown wheat mite is a small brown mite, half a pinhead in size. Damage, like the blue oat mite, is only severe in dry seasons. Feeding causes a fine mottling of the leaves and the damage gives the appearance of drought effects. When heavily infested crops are viewed from a distance they have a bronzed or yellowish appearance.
Damage: mites are seen most commonly during the late afternoon when they begin feeding on the leaves. This continues throughout the night and results in a silvering of the leaf tips. When infestations are severe the leaf tips wither and eventually the seedlings die. Damage is most likely during dry seasons where the mite is in large numbers making moisture stress worse. Control may be warranted in this situation. Adults and nymphs pierce and suck on leaves resulting in silvering of the leaf tips in cereals. When heavy infestations occur, the leaf tip withers and the seedling can die. In canola, leaves are mottled or whitened in appearance.
Monitoring and control: Check from planting to early vegetative stage, particularly in dry seasons. Blue oat mites are most easily seen in the late afternoon when they begin feeding on the leaves.
Where warranted, foliar application of registered insecticide may be cost-effective if applied within 2-3 weeks of emergence in autumn. Since eggs laid in the soil hibernate throughout the winter, populations of the mite can build up over a number of years and cause severe damage if crop rotation is not practiced.
Cutworms
Cutworm larvae
Several species of cutworms attack establishing cereal crops in Queensland and NSW. As their name suggests cutworm larvae sever (cut) the stems of young seedlings at or near ground level, causing the collapse of the plant.
Cutworm larvae are up to 50 mm long, hairless with dark heads and usually dark coloured bodies, often with longitudinal lines and/or dark spots. Larvae curl up and remain still if picked up.
Damage: Cutworms are soil inhabiting pests of mainly young plants. They usually feed at night and seek refuge in the soil by day. They normally attack seedling plants by cutting through their stems near ground level but they may also feed on the foliage of older plants. Most damage is done between germination and tillering. Damage usually shows up as general patchiness or as distinct bare areas in a very short time. Young caterpillars climb plants and skeletonise the leaves or eat small holes. The older larvae may also climb to browse or cut off leaves, but commonly cut through stems at ground level and feed on the top growth of felled plants. Caterpillars that are almost fully grown often remain underground and chew into plants at or below ground level.
Monitoring and control: Inspect crops twice weekly in seedling and early vegetative stage. The best time to monitor is late afternoons and evenings when larvae feed. Chemical control is warranted when there is a rapidly increasing area or proportion of crop damage. If distribution is patchy, spot spraying may suffice. Chlorpyrifos and various pyrethroids are mainly used to control cutworm.
Cultural control measures include weed control - at least 3-4 weeks prior to sowing.
Cutworms are soil inhabiting pests of mainly young plants. They usually feed at night and seek refuge in the soil by day. They normally attack seedling plants by cutting through their stems near ground level but they may also feed on the foliage of older plants. Most damage is done between germination and tillering. Damage usually shows up as general patchiness or as distinct bare areas in a very short time.
The larvae mature in about four weeks but in cooler conditions this may be much longer.
Controlling weed growth in the fallow prior to planting will greatly assist in reducing cutworm population and reduce crop damage. Chemical control may be warranted at levels of one larva/square metre in emerging crops.
