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Pests to look out for in coming weeks

As the winter growing season draws to a close, remain vigilant for diamondback moths, armyworms, snails and Rutherglen bugs among others

Diamondback moth (DBM) 

DBM larvae surface graze on plants; they wriggle furiously if disturbed (Source: cesar)

Diamondback moths (Plutella xylostella - DBM) attack canola and other brassica crops. Thresholds are quite high for crops at seed set. They can be particularly problematic in forage brassicas and spring-sown canola during late spring and summer. A large influx of adult DBM was sighted approximately two weeks ago within horticultural brassica crops and weeds in the Central Tablelands and Hunter districts of NSW. This has resulted in large numbers of eggs being deposited in crops in these districts. DBM are also present in many Victorian districts, but reportedly in low numbers. DBM larvae feed inside leaf tissue when they are small, and it is only the 2nd and 3rd instar larvae that can be targeted with insecticide. Insecticide resistance is common in DBM and often two applications of insecticide are needed to eliminate the population. For more information refer to Diamondback moth within the new PestNote series.


Armyworms in cereals

Armyworms are most damaging when they climb and sever cereal stems below the head (Source: SARDI).

Armyworms (Family: Noctuidae) can become major pests within cereal crops and grasses as they approach maturity at this time of year. They sometimes feed on the remaining green material just below the maturing head of cereals, causing heads to fall. Ripening barley crops are generally worst affected. The first visible sign of armyworm caterpillars is often their green or straw coloured droppings, about the size of a match head, found on the ground between cereal rows. Monitoring for armyworms at dusk in vulnerable crops, particularly barley, is highly recommended. For more information refer to Armyworm within the new PestNote series.


Snails in maturing cereals

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

Snails can cause contamination issues in grain when they are present above cutting height in the canopy (or in windrows) and harvested along with the grain. 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 some grain wastage. Identifying snail species and monitoring numbers before harvest, and before and after control operations is essential.

For more information on snails, refer to pointed snail, small pointed snail, vineyard snail or white Italian snail within the new PestNote series.


Rutherglen bugs in canola

Rutherglen bugs can swarm onto crops in late spring and early summer (Source: cesar).

Reports from Queensland and northern NSW suggest that there have been recent flights of Rutherglen bug (Nysius vinitor), affecting canola in particular. Rutherglen bugs are native insects that attack a wide range of weeds and crops in the warmer months. They can arise from weeds beneath a crop, or migrate into the crop on warm northerly winds. They are well adapted to dry warm weather and are often most damaging to moisture-stressed plants. They can invade windrows in vast numbers, 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 more information refer to Rutherglen bug within the new PestNote series.


Source of field reports

Melina Miles – Entomologist, Queensland Department of Agriculture and Fisheries (Toowoomba)

Andy Ryland – Crop Protection Consultant, IPM LLC (Sydney Metropolitan)

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