Pest Facts July 2009

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17 Jul 2009
By Paul Umina

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.

CONTENTS

Lucerne Flea and Other Springtails

Yellowheaded Cockchafers

Earwigs

Grey-banded Leaf Weevil

Online Reporting Proforma

LUCERNE FLEA AND OTHER SPRINGTAILS

Lucerne flea (Sminthurus viridis) have been reported causing damage to a barley crop which was undersown with lucerne, east of Griffith in the Riverina district of New South Wales. Some damage was present on both the barley and the lucerne plants and control options are currently being considered. Lucerne flea are typically present from autumn to spring and can be problematic throughout this period.

Adult lucerne fleas are approximately 3 mm long and green-yellow in colour. They work up the plants from ground level, eating tissue from the underside of the foliage. They leave distinctive feeding damage of ‘windows’ of transparent leaf membrane and ‘spring’ or jump off vegetation when disturbed. Click here for images of the lucerne flea. High numbers of small (1-2 mm long), dark purplish-black coloured collembola (or ‘springtails’) have been sighted in various crops in the Riverina and South West Slopes districts of New South Wales, as well as the Western district of Victoria. Researcher, Ange Tsitsilas (CESAR) reports observing ‘thousands per square metre’ of these springtails in paddocks between Geelong and Hamilton recently.

According to researcher, John Roberts (CESAR), they are members of the Hypogastruridae family, and despite the high numbers which are often detected, John says they are unlikely to be feeding on crop plants. Collembola are soil and litter dwelling insects that prefer wet, damp surroundings. They lack wings and always have antennae. They are among the most abundant of all soil-dwelling insects.

Co-ordinators: Paul Umina TEL: 03 8344 2522 EMAIL: pumina@unimelb.edu.au

Stuart McColl TEL: 03 9329 8816 EMAIL: stuart@cesarconsultants.com.au

YELLOWHEADED COCKCHAFERS

Agronomist, Tim McNamara (McNamara’s Country Store), reports finding yellowheaded cockchafer larvae (Sericesthis spp.) in a wheat paddock near Rutherglen, in the Northeast district of Victoria. The grubs found ranged from 5-15 mm long, and despite the high numbers (up to 8 grubs per shovel) they do not appear to have caused any damage to the crop at this stage. The crop established with excellent vigour, however, Tim says there is some concern about potential damage given the high numbers of grubs present and the lack of alternative vegetation in the paddock.

Yellowheaded pasture cockchafer larvae are “C” shaped, creamy-grey in colour and have a yellow head capsule. When fully grown in winter they are about 25-30 mm long. The grubs live in the soil until mid-to-late summer, where they emerge as yellow-reddish beetles about 10-15 mm in length. Unlike blackheaded cockchafers, which come to the surface to feed, yellowheaded cockchafers are primarily root feeders.

There are no insecticides that provide effective control of yellowheaded cockchafers due to their subterranean feeding habits. Cultural control methods including pasture renovation, re-sowing bare areas using a higher seeding rate, and cultivating affected areas prior to sowing may be the best methods for control. Predatory invertebrates and insectivorous birds also play an important role in keeping cockchafer populations in check.

To check paddocks for cockchafers, dig in the affected areas or look on the soil surface for tunnel entrances. Be aware that if you did not have problems with cockchafers last year, it does not mean that you won’t have this year. Adult beetles achieve long distance dispersal by flying, usually at dusk on warm evenings around late November. Click here for images of yellowheaded cockchafers.

EARWIGS

Several growers in the Western district of Victoria have reported damage to young canola plants and suspect European earwigs (Forficula auricularia) are the cause. Both adults and young nymphs have been found in affected crops. In the past, European earwigs have been known to devastate patches of canola crops in parts of the western district, and they can be difficult to control with conventional insecticides.

European earwigs are an introduced species that have been spreading in southern agricultural areas, probably by transport in hay, machinery or household pot plants. They are an emerging pest of canola, mainly on heavier soil types. It is believed that their numbers have increased in recent years due to intensive cropping and stubble retention, which improves the habitat for earwigs.

Adult European earwigs range from 12-20 mm long, are smooth and shiny dark brown in colour with pale yellow legs. They have distinctive “pincers” that protrude from their rear end and look very similar to native earwigs, which are commonly found around household leaf litter. Native earwigs rarely damage plants and are generally not significant pests.

European earwigs are nocturnal (therefore monitoring should be conducted at night) and shelter in dark spaces, such as under trash or cracks in the soil, during the day. They feed on the developing leaves of seedlings, slowing down plant development, and in some cases killing the plants. Irregular shaped holes are typical of earwig feeding. They can also chew through canola pods, causing seed development to stop, and contaminate windrows at harvest time.

European earwigs tend to only become a problem if populations become large. Reducing stubble residue may lead to a decrease in earwig numbers. The burning of stubbles in paddocks known to harbour earwigs has been shown to give satisfactory control but this has limited application as it can lead to wind erosion.

A reminder that it is important to know the difference between this species and native earwigs, particularly the common brown earwig (Labidura truncata). The common brown earwig is predatory, feeding on soft-bodied insects, such as caterpillars, redlegged earth mites and lucerne flea. It can be distinguished by the presence of an orange coloured triangle behind the head on the elytra or ‘wing-case’.

GREY-BANDED LEAF WEEVIL

Consultant, Tim Condon (Delta Agribusiness), reports finding very high numbers of small grubs feeding on marshmallow weed in paddocks throughout the South West Slopes district of New South Wales. These have been identified as larvae of the grey-banded leaf weevil (Ethemaia sellata). Tim says they have been noticed over the past few years however this year they appear to be present in significantly higher numbers. Some marshmallow plants have been completely defoliated, including some damage to the stems, however no crops appear to be coming under attack at this stage.

Grey-banded leaf weevil larvae have also been identified for agronomist, Elissa Strong (AGnVET Services), who reports finding them in various paddocks around Forbes, in the Central West Slopes & Plains district of New South Wales. Elissa says they appear to be widespread around the district and in all cases they have been found associated with marshmallow weed. As yet, no damage has been detected on any adjacent cereal crops.

Little is known about the feeding ecology of grey-banded leaf weevils. Adults are known to attack several winter crops including canola and lupins, and may also be a grain contaminant at harvest. It is thought that they may feed preferentially on malvaceous weeds (such as marshmallow weed) and some ornamental plants, and these could be the source of infestations in crops. This species has been recorded as common in gardens, and both adults and larvae are known to attack several ground vegetables. Larvae are yellow to green in colour with a light green to brown head capsule, and are often confused with vegetable weevil larvae, which are similar in size and colour. They are legless and grow to approximately 5-8 mm long. Adult weevils are approximately 8 mm long, grey in colour with distinctive raised markings (bumps) and a white area on the bottom covering approximately 1/4 of the wing covers (elytra). Adults are thought to be flightless. Eggs are laid on plant leaves and pupation occurs in the soil.

Crops should be monitored closely, particularly near fence-lines, as adults tend to move into crops from host weeds and scrub. There are no insecticides currently registered to control grey-banded leaf weevils. However, when synthetic pyrethroids have been used at 400mL/ha against other pests, they are reported to provide adequate control of grey-banded leaf weevil. Previous reports also suggest that canola paddocks sown with insecticide-treated seed experience less feeding damage from weevils.

ONLINE REPORTING PROFORMA

A reminder about the observational reporting proforma which is available online to facilitate the reporting of invertebrate issues and occurrences in south-eastern Australia. The aim of this form is to make the reporting process more efficient and simpler for PestFacts subscribers in South Australia, Victoria and New South Wales.

Information collected is standardized, 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, and click here to view instructions for collecting and sending insects for identification.

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 beneficials) in crops and pastures, contact Stuart McColl on (03) 9329 8816 or email stuart@cesarconsultants.com.au. A free pest identification service is available to all PestFacts subscribers.

Disclaimer: Any recommendations, suggestions or opinions contained in this publication do not represent the policy or views of The University of Melbourne (Uni Melb), CESAR Consultants (CESAR) and the Grains Research and Development Corporation (GRDC). No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. Uni Melb, CESAR and GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information presented in PestFacts. The content that is referenced and hyperlinked to in this service is outside the control of Uni Melb, CESAR and GRDC. It is the responsibility of users to make their own decision about the accuracy, currency and reliability of this information. Permission of the publisher is required for reproduction. Copyright © Uni Melb 2009.

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