Potential pests on the horizon

The end of the winter-cropping season is in sight. Here are a few potential pests to look out for over the coming weeks and through summer

 

Snails

Grain contamination

Above average rainfall in winter and spring across most of south-eastern Australia means conditions are ripe for snail activity. Contamination issues can occur in grain when the snails accumulate in the canopy above cutting height (or in windrows). This can lead to clogging of machinery and/or quality downgrades.

Harvester modifications and grain cleaning will help to ensure grain is successfully delivered, but these usually incur grain wastage. Identifying snail species and monitoring numbers before harvest, and before and after control operations is essential.

Snail management at harvest involves: 

(i) minimising the intake of snails into the header,

(ii) maximising the separation of snails and grain within the header, and

(iii) cleaning harvested grain. 

There is usually a trade-off between snail removal from grain and grain wastage. Reducing snail intake is more achievable early in the harvest season as fewer snails will have moved into the crop canopy. This movement is dependent on rainfall events that will trigger snail movement down the canopy. Snails are more easily dislodged from plants when they have not “fixed” themselves higher in the canopy.

Harvest techniques include:

•Harvesting snail infested crops first, particularly after a rain/moisture event

•Windrowing cereal crops will dislodge some round snails (but watch for re-invasion of green-cut windrows left to dry)

•‘Dislodger bars’ attached to the header knock a proportion of round snails and are most effective in early harvested or windrowed crops

•Stripper fronts can significantly reduce snail intake in cereal crops, or alternatively raise the cutting height

•Sieves and mesh screens should be set up correctly to maximise snail and grain separation within the header

•Post harvest grain cleaning is the last opportunity for snail removal. A combination of systems is usually required to meet receival standards without excessive grain losses.

 

White Italian snails settle on maturing stubble and can create a major grain contaminant (Source: SARDI).

 

Managing snails into summer

Research is showing that snails may become surface active after summer rainfall, but do not always actively feed at this time. Baiting should occur before they lay eggs and is more likely to be effective in March. Snails can start laying eggs in autumn once soil is moist, the timing of which varies between seasons. However, after a decent rain a sample bait may be applied to determine if snails are indeed feeding. Information gathered from this can assist in determining the necessity to apply bait across the entire paddock.

When considering summer snail control, the decision to use cabling, rolling and windrow burning should be weighed against whether it is desirable to retain stubble. If burning snails is the chosen strategy, windrows should be set up at harvest. Retained moisture in windrows will attract snails over summer and the snails can be then burned with windrows when safe to do so. This strategy is not as effective for small pointed snails (Prietocella barbara).

Summer weed control should be carried out after creating windrows to remove alternative habitats where snails can seek refuge and source moisture during the dry months. With the removal of weeds, the snails will be forced to remain in stubble and/or windrows where cabling, rolling or burning can be utilised.

Success with cabling or rolling in summer depends upon high temperature. Choose a day where air temperatures reach 35-40°C (ground temperature about 55°C); at these temperatures snails knocked to the ground will dehydrate and die. Take care to avoid causing fire when cabling.

For further information on control methods refer to GRDC publications: Snail Management Fact Sheet or Bash 'em, Burn 'em, Bait 'em.  For further information on individual snail species, refer to pointed snail, small pointed snail, vineyard snail or white Italian snail PestNotes.

 

Rutherglen bugs

Rutherglen bug (Source: cesar)

The Rutherglen bug (Nysius vinitor) is a native insect that attacks a wide range of weeds and crops in the warmer months.  They are a sucking pest that uses their mouthparts to pierce stems, buds, flowers and pods, including pods with maturing grain. They can arise from weeds beneath a crop, or migrate into the crop on warm northerly winds from distant locations. They are well adapted to dry warm weather and are often most damaging to moisture-stressed plants.  They are most prominently found on pre and post-windrowed canola, often in vast numbers, as seen in this QDAF clip. They can persist in windrows, searching out the last remnants of green plant material.

Consequently, adults and nymphs can become a grain contaminant when in high numbers.

Highest numbers of Rutherglen bugs are often observed along crop perimeters. Populations will increase with the warmer weather conditions and can reach damaging levels very quickly. Check crops over the coming weeks, particularly canola, linseed and sunflowers. Contamination can be minimised by attaching screens to headers or by harvesting at night. As Rutherglen bugs can readily re-invade a sprayed area, insecticide application will not guarantee a clean sample.

For further information on Rutherglen bugs refer to this PestNote.

 

Bronzed field beetles

Adult bronzed field beetles (left) (Source: Copyright © Western Australian Agriculture Authority, 2015)

 

Bronzed field beetles (Adelium brevicorne) are a pest of establishing crops during autumn and early winter in some areas of southern NSW and Victoria. The larvae (a false wireworm) are particularly problematic in emerging canola crops that are sown into heavy stubble. Adult beetles start to emerge from mid October and will begin to accumulate under and in windrows.

The flightless beetles, which grow to about 11 mm with a shiny black to bronzed appearance, can then become grain contaminants.

Because of the flightless nature of this pest, infestations are more likely to carry over from one year to the next in the same paddock. Hence, an understanding of which paddocks are harbouring large populations provides a basis for more satisfactory control in subsequent years. We advise that, in pest prone areas, windrows are harvested as soon as possible, preferably through the hottest part of the day, which will reduce beetle loads.

When growers are planning for the following cropping season, it is also worth noting that the next generation of the pest can be controlled in summer. Trials in WA have shown that removal or disruption of the surface plant material in February/March (where it is considered to be an appropriate practice) will reduce or eliminate bronzed field beetle by preventing egg-laying. This may be achieved through cutting and baling, grazing or burning.

For further information on bronzed field beetles refer to this PestNote.