Pest Facts South East Issue One

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10 May 2010
By Stuart McColl

PestFacts is a free service designed to keep you informed about invertebrate pest-related issues - and solutions - as they emerge during the winter growing season. The service is supported by the GRDC's National Invertebrate Pest Initiative, with a focus on pests of broad-acre grain crops in south-eastern Australia.

Co-ordinators: Paul Umina & Stuart McColl
TEL: (03) 9329 8816
EMAIL: stuart@cesarconsultants.com.au

CONTENTS

• Australian Plague Locusts
• Weed Web Moth
• Spotted Alfalfa Aphid
• General Aphid Warning
• Look Out For Other Invertebrate Pests
• Observational Reporting Proforma

AUSTRALIAN PLAGUE LOCUSTS

Continued widespread heavy rainfall during summer and autumn has created favourable conditions for the development of Australian Plague Locust (Chortoicetes terminifera) populations in parts of New South Wales, South Australia and Victoria.

To date, we have received numerous reports of locust activity in parts of western and north-western Victoria, and southern New South Wales. In several instances locusts have been reported attacking early-sown crops emerging in these regions, including canola and wheat.

The current locust swarms have resulted from widespread summer rains in locust breeding grounds in the northern Channel Country areas of south-west Queensland and adjacent areas of South Australia, New South Wales and the Northern Territory. Rain has created ideal conditions for locust breeding, triggering significant egg hatch and providing an abundance of green material for locusts to continue their development and build up to large numbers. Adults have subsequently migrated hundreds of kilometres south on favourable winds into southern cropping areas looking for green feed. Growers and agronomists in all cropping regions should remain vigilant and continue to be on the lookout for locusts on their properties and in surrounding areas. The current adult locusts are likely to remain active until around mid-June, before they die off with the onset of colder weather. At the moment, it is particularly important to be on the lookout for any egg-laying activity, as this is likely to mean high numbers of locusts hatching in spring. Female locusts prefer to lay eggs into hard, bare ground or heavy soil types, although some laying in lighter soils has been observed. Where significant egg-laying has been detected, deep cultivation is thought to help reduce egg survival.

Any significant locust activity should be reported to your relevant Department of Primary Industries or directly to the Australian Plague Locust Commission (APLC). The APLC undertakes monitoring and forecasting of locust populations in inland eastern Australia throughout the year. They also coordinate broad scale control programs across Queensland, New South Wales, Victoria and South Australia. The New South Wales plague locust commissioner, Ross Burton, says control efforts this year have been made particularly difficult because seasonal conditions have resulted in low to medium densities of mixed-age locusts spread across a wide area. Locusts are notoriously difficult insects to control as large populations can move vast distances in a short period of time. In addition, adults have been known to feed in paddocks during the daytime but may move several kilometres away each night to roost in sheltered areas such as remnant vegetation or windbreaks, before resuming feeding in the paddock the following day. Ideally, locusts should be controlled as ‘hoppers’ when they are unable to fly. However, if targeting adult locusts with chemicals, spraying should occur when they are settled, either in the late evening or very early morning. Adjacent paddocks, particularly pastures, should also be monitored and treated if required. Australian plague locusts can cause severe damage to pastures and a range of field crops if they are not controlled. They are readily distinguished from other locust species by the large dark spot present on the tip of each hind wing and red coloured shanks on their hind legs. Adults are up to 40 mm long with a variable body colour of grey, brown or green. They are the most important pest species of locust in Australia due to the area infested and frequency of plagues.

WEED WEB MOTH

We have identified weed web moth caterpillars (Achyra affinitalis) for agronomist, Brett McEwan (I.K. Caldwell). Brett reported finding them attacking medic in a paddock near Kerang, in the northern country district of Victoria. Plants had been completely defoliated in some areas, and characteristic webbing was evident around the plants. Brett says they appear to be starting out in sandy areas and spreading out over time. District agronomist, John Fowler (I&I NSW), has also reported small caterpillars, attacking various weeds around Deniliquin, in the Riverina district of New South Wales. These have also been identified as weed web moth, and John says they are very common in the district at the moment. John has found them on weeds such as Bathurst burrs, boxthorns and roly-poly, as well as some native ground creepers.

Weed web moth caterpillars are known to attack canola, soybeans, lupins and lucerne. They feed under a fine web, skeletonising foliage and webbing leaves together. They may shred the leaves of seedling crops and cause complete defoliation, which can lead to plant death. Control is occasionally warranted when large numbers build up, typically where there is an abundance of green plant material over spring and summer. However, difficulties have occurred in the past because this pest requires higher rates of insecticides than commonly used against cutworm and pasture webworm.

Weed web moth caterpillars are grey-green and pale brown in colour, with a distinctive black head. They are slender, grow up to 15 mm long and generally have a dark line down the middle of their back with three rows of dark spots on either side. Caterpillars tend to wriggle violently or crawl around rapidly when disturbed. Moths have a 20 mm wingspan and are buff coloured with darker brown or reddish flecks, mainly on the forewings.

SPOTTED ALFALFA APHID

Spotted alfalfa aphids (Therioaphis trifolii) have been identified for agronomist, Allan Edis (AGnVET Services), from a lucerne paddock near Henty in the Riverina district of New South Wales. Very high numbers of aphids were found across the paddock and their feeding has visibly affected many plants. Allan says plants are showing signs of yellowing and wilting, and in some cases plant death is likely to occur if aphids are not controlled. The paddock is currently in its third year of lucerne, and has not previously experienced problems with aphids. Spotted alfalfa aphids are a pest of lucerne, legumes and annual medics. Adults and nymphs suck sap and inject a toxin into the plant. Initial symptoms are a yellowing or whitening of the leaf veins. Leaves may then turn yellow, wilt and fall. Damage proceeds from the base of the plant upwards, until only stems remain standing. Stems can become sticky with honeydew exuded by the aphids. Early planted pastures are at risk from spotted alfalfa aphids, which are favoured by warm autumns, particularly following an early break.

Adult spotted alfalfa aphids are pale yellow-green in colour and can be up to 2 mm long. They have at least 6 rows of tiny black spots on their back, which are just visible to the naked eye. Nymphs are similar but smaller in size. A good magnifying glass or a microscope will make this species readily identifiable. Spotted alfalfa aphids are generally found on the underside of leaves and adults may have wings. When disturbed, adult aphids jump in ‘showers’ from plants. Allan says when checking the affected paddock, aphids could be found all over plants as well as on the ground.

GENERAL APHID WARNING

Summer and early autumn rainfall in many regions has resulted in significant growth of weeds and volunteer crop plants which can act as alternative hosts for many aphid species. A good ‘green bridge’ enables aphids to survive between cropping seasons, and can result in high numbers of aphids present around the time of crop emergence. At this time winged aphids move into crops, and when aphid numbers build up they can damage crop plants directly by feeding on plant sap and nutrients. Aphids that arrive in crops in autumn and persist in low numbers over winter can also lead to large, damaging populations that peak in late winter and early spring. Importantly, aphids are also vectors of several important plant viruses and the potential severity of these is greatly increased when they are transmitted to plants early in the season. Effectively controlling weeds and crop volunteers well in advance of sowing is a good way to reduce the risk of aphids moving into newly established crops. At this time of year it is important to inspect green weeds, volunteer plants and roadside verges for the presence of aphids which will indicate the likely occurrence in nearby crops in the coming months. Farmers, particularly those in virus prone areas, are also advised to pay close attention to crops, looking for signs of wilted or stunted growth. If chemical control is required, selective insecticides (e.g. pirimicarb) are available, which are aphid specific and less harmful to other invertebrates including beneficial natural enemies of aphids. If spraying in autumn, insecticides are often most effective if applied soon after aphids begin moving into crops from surrounding vegetation. If detected early, a border spray may be all that is necessary. Waiting too long could result in some plant infestation and issues with virus control later in the year. Another option is to use insecticide-based seed dressings, as they can delay aphids from entering crops for up to six weeks after emergence and delay the need for foliar sprays.

LOOK OUT FOR OTHER INVERTEBRATE PESTS

Redlegged Earth Mites and Blue Oat Mites hatch from summer diapause eggs in autumn, triggered by colder weather and significant rainfall. Swarms of mites can attack delicate crop seedlings and emerging pasture plants. Earth mites attack pastures and a variety of crops such as cereals, oilseeds, lupins and lucerne, as well as a variety of weeds. We have received reports of redlegged earth mites and blue oat mites in some cooler regions of Victoria, and they are likely to become widespread in the near future.

Cutworms can be a problem to a variety of germinating crops. Prolonged autumn green feed in areas can allow grubs to develop to a large size by the time crops start emerging. Check crops, especially pulses and pasture legumes, by inspecting the base of plants; damage is often patchy. Slugs are stimulated out of their summer aestivation following autumn rains, generally in paddocks were they have previously been a problem. All seedling crops and pastures may be attacked, however canola is particularly susceptible. Slug numbers can be monitored by placing tiles or flowerpots on the soil surface and counting the number under them after a few days.

OBSERVATIONAL REPORTING PROFORMA

PestFacts relies on valuable field observations of pest occurrences. Your contributions make this service more informative and helpful for the management of invertebrate pests. An observational reporting proforma is available on-line to facilitate the reporting of invertebrate issues and occurrences in south-eastern Australia. It is hoped this will make the reporting process more efficient and simpler for PestFacts subscribers. The use of this form will ensure the information collected is standardised, allowing us to track on-going changes in pest importance/abundance, as well as being able to address future issues on national and regional scales (e.g. changing distributions, widespread problems versus localised problems, impacts of climate change).

Click here to view the NIPI reporting proforma and/or to make a pest report. Please note that this new service does NOT replace the ‘traditional’ reporting methods of email or a phone call; these are still very welcome.

PESTFACTS SERVICE

PestFacts is sent directly to readers via e-mail (subscription free). This service is produced on an ‘as-needs’ basis in response to pest observations and reports. Your support and feedback are essential to the success of PestFacts. If you have recently observed invertebrate pests (or beneficial species) in crops and pastures, contact Paul Umina or Stuart McColl on (03) 9329 8816 or by email stuart@cesarconsultants.com.au.

A free pest identification service is available to all PestFacts subscribers.

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