Slaters and other winter cereal establishment pests

In recent days we have received a number of reports of slater activity in winter cereal crops in southern Queensland and northern NSW.

Slaters are not generally regarded as a pest of broad acre agriculture and tend to feed on decaying vegetation and dead animal matter. Overall they perform an important recycling role in the environment however on rare occasions they can also attack seedlings of broad acre crops.

Slaters are woodlice and they are crustaceans, not insects. They have a hard skeleton on the outside and many pairs of jointed legs. The native slater species doing the damage to cereal crops is Australiodillo bifrons. This species has a light brown oval shaped and flattened body with a dark brown stripe in the middle of the back. Both males and females have a characteristic split on the frontal plate. Males tend to be larger than females and can grow as large as 9 mm long and 6.5 mm wide.

This native slater is commonly found in low lying swampy regions and tends to be more active after rain periods. They need damp conditions and will die if exposed to open and dry situations.

Slaters are an agricultural pest in South Africa where they are generally controlled by cultivation. Changing farming practices such as minimum or non tillage seem to have worsened the slater problem, especially if there is also a large amount of stubble present in fields.

Slaters are known to do damage to seedlings of wheat and oats and there is also evidence of slater activity in canola in western and southern Australia. It is not known if other crops are hosts for slaters.

Damage: Slater damage looks similar to snail and slug damage with rasping and shredded appearance to leaves. Feeding damage can also appear as irregular patches removed from the leaves resulting in distinctive ‘windows’ of transparent leaf membrane. Thousands of seedlings can be eaten in a short time by swarms of slaters.

Control: There are no registered pesticides for the control of slaters in winter cereals. Non chemical approaches such as providing alternative habitats may decrease slater numbers in crops. Shelterbelts containing a complex understorey of vegetation and soil litter may be more attractive to slaters. Such environments also harbour many natural enemies of broad acre insect pests which can also keep slater populations in check.

Other winter cereal seedling pests

Cutworms
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: 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.

Blue oat mite
The blue oat mite is an important pest of seedling winter cereals. When infestations are severe the leaf tips wither and eventually the seedlings die. Eggs laid in the soil hibernate over winter, allowing populations to build up over a number of years, causing severe damage if crop rotation is not practised.

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 redlegged earth mite.

Damage: 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.

Know your seedling pests
Correct identification of pests feeding on cereal seedlings is important as this will influence selection of control options.

Article by Kate Charleston and David Murray

Fleabane alert
Following the recent rain, the first main flush of fleabane for the year will start to emerge shortly. Whilst this weed is often regarded as one of the most difficult-to-control weed, it is much easier to control when it is a small seedling. So, growers need to be alert and think about spraying soon.

To assist growers and consultants, the weeds team has recently published a brochure on fleabane, and it is available from the Queensland Primary Industries & Fisheries website http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/26_4251_ENA_HTML.htm

The team is also developing a best practice herbicide guide, using feedback from consultants on what is being used successfully for in-crop and fallow control across the region.

If you wish to be part of this short survey, please contact Michael Widderick on Michael.widderick@dpi.qld.gov.au or Steve Walker on steve.walker@dpi.qle.gov.au