Pest Facts South East Issue Three

Print version

24 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.

CONTENTS

• Update on Australian Plague Locusts
• Bryobia Mites
• Lucerne Flea
• Aphids in Lucerne
• Cutworms
• Leafhoppers

UPDATE ON AUSTRALIAN PLAGUE LOCUSTS

Australian plague locusts (Chortoicetes terminifera) are continuing to cause extensive damage to autumn sown cereal, canola and fodder crops across north-western Victoria, south-western New South Wales and parts of South Australia. The current level of swarming activity remains very high, and is somewhat unusual for this time of year. According the most recent update from the Australian Plague Locust Commission (APLC), swarm densities were predicted to decline during May. However, continued dry and mild weather conditions over recent weeks appear to have facilitated ongoing locust activity.

In addition to the mature locust swarming activity, there have been sightings of young locust nymphs this week in parts of New South Wales and north-western Victoria. Senior Technical Officer, Ken Henry (SARDI), says these isolated hatchings are unusual and may not survive over the winter months. The majority of eggs laid in recent weeks are diapause eggs and will remain in the soil over winter, hatching out in spring. Ken says locust numbers are slowly declining with the cold weather and the occurrence of frosts in many regions. It is now highly unlikely that there will be any further large migration of locust swarms from northern areas.

As a result of locust activity and egg-laying to date, there is expected to be a serious widespread nymph infestation in spring. Areas affected include much of New South Wales, northern Victoria and eastern South Australia. A plague situation consisting of high locust densities across several states may continue throughout spring and into summer if nymph survival in spring is high. The Australian Plague Locust Commission (APLC) has published predicted locust hatching dates in spring for various towns in New South Wales, Victoria and South Australia, based on the observed egg-laying dates from recent weeks. Hatching dates are available on the APLC website and some examples are: Mildura-Ouyen (VIC) - 7th October, Narrandera-Griffith (NSW) - 10th October, Swan Hill-Boort (VIC) - 16th October, Parkes-Cowra (NSW) - 18th October, and Wagga Wagga–Cootamundra (NSW) - 25th October.

BRYOBIA MITES

Consultant, Glen Smith (3D-Ag), has reported bryobia mites (Bryobia spp.) in an emerging canola crop south of Lockhart, in the South West Slopes of New South Wales. The mites have caused significant damage to a large part of the paddock, which was sown to cereals last year. Glen says in the worst affected areas, 1-2 mites can be seen per cotyledon and there is an obvious difference in plant development compared with plants in other parts of the paddock where no or few mites are present. The paddock was treated with endosulfan several weeks ago but mites are still being found. Similar situations have been reported in previous years where paddocks have been treated with endosulfan as a post-sowing, pre-emergent spray to control bryobia mites.

Agronomist, Craig Drum (Tatyoon Rural), has also reported bryobia mites in two canola paddocks and a clover/pasture paddock near Tatyoon, in the Western district of Victoria. Although high numbers have been observed, Craig says there has been limited damage. Given bryobia mite numbers are likely to decline significantly as conditions become cooler and wetter, these paddocks will not be sprayed but monitored over the next few weeks.

Bryobia mites are an important pest of clovers, canola, wheat and lupins. Often called the ‘clover mite’, bryobia mites are less than 1 mm long with a fawn-orange coloured body and orange legs. In the field they are often misidentified as the redlegged earth mite. Bryobia mites can be distinguished by their long forelegs, which are about 1.5 times their body length. Unlike most other earth mite species, bryobia mites are most active in warm conditions in autumn, spring and summer. These mites are generally found in low numbers and are unlikely to be problematic over the winter period.

Bryobia mites can be difficult to control with pesticides, and they are often reported to persist in the field following chemical applications aimed at other mite species. Recent findings by CESAR have found that organophosphates may provide better control of bryobia mites than synthetic pyrethroids.

LUCERNE FLEA

There have been several reports of lucerne flea (Sminthurus viridis) hatchings in parts of Victoria and southern New South Wales. Researcher, John Roberts (CESAR), reports finding lucerne flea nymphs in several pasture paddocks around Colac, in the Western district of Victoria. Agronomist, Greg Parker (Mangoplah Farm Centre), has found lucerne flea in two paddocks of established lucerne south of Wagga Wagga, in the South West Slopes district of New South Wales. To date, there has been little feeding damage observed but the paddocks will be closely monitored. Agronomist, John Jervois (Tarcutta Rural Supplies), has also reported lucerne flea hatchings near Tarcutta, in the South West Slopes of New South Wales. Most hatchings have occurred in low-lying areas within newly emerging pastures and older established lucerne stands. John says some paddocks are likely to need some control to protect young seedlings.

Lucerne fleas hatch following periods of good soaking autumn-winter rainfall and can cause significant damage to emerging crops and pastures at this time of year. They can also cause considerable damage to older crops if numbers build up under favourable conditions throughout the season. With the lack of recent rainfall experienced across much of south-eastern Australia, lucerne flea hatchings may be delayed and somewhat staggered in many regions.

Adult lucerne fleas are approximately 3 mm long and appear yellow-green to the naked eye, although their globular abdomens are often a mottled pattern of darker pigments. They ‘spring off’ vegetation when disturbed. Lucerne fleas have a wide host range and will attack most broad-acre crops, including canola, lucerne, pastures, cereals and some pulses. Feeding results in the appearance of distinctive transparent ‘windows’. They are generally a problem in regions with loam/clay soils.

Crops should be inspected frequently at and immediately following emergence, when they are most susceptible to damage. Paddocks are most likely to have problems where they follow a weed infested crop or a pasture in which the lucerne flea has not been controlled. There are several options available to growers for controlling the lucerne flea. Foliar insecticides can be applied approximately three weeks after lucerne fleas have been observed in a newly emerged crop. This will allow for further hatching of over-summering eggs but will be before lucerne flea reach the adult stage and begin to lay winter eggs. If spraying is required, do not use synthetic pyrethroids.

In paddocks where damage is likely, a border spray may be sufficient to prevent movement of lucerne fleas into the crop from neighbouring paddocks. As lucerne fleas are often distributed patchily within crops, spot spraying is generally all that is required; do not blanket spray unless the infestation warrants it. Snout mites (which have orange bodies and legs) are effective predators of lucerne fleas, particularly in pastures, where they can prevent pest outbreaks. The complex of beneficial species (including snout mites) should be assessed before deciding on control options.

APHIDS IN LUCERNE

Agronomist, Greg Parker (Mangoplah Farm Centre), has reported aphids in several lucerne paddocks south of Wagga Wagga, in the South West Slopes of New South Wales. Both spotted alfalfa aphids (Therioaphis trifolii) and bluegreen aphids (Acyrthosiphon kondoi) have been observed in fairly high numbers. Greg says the summer and early autumn rainfall has resulted in a ‘green bridge’ that enabled aphids to survive in high numbers over the summer period. The paddocks containing aphids are established lucerne crops, with some having a history of aphids in previous seasons.

Bluegreen aphids are a large species, measuring up to 3 mm long as adults. Both the winged and wingless forms are a matt bluish-green colour. Annual medics, lucerne, subterranean clover and lupins are susceptible to bluegreen aphids. In lucerne and medics, heavy infestations cause stunted growth, leaf curling and leaf drop. In subterranean clover, leaves wilt before turning brown and dying. Bluegreen aphids favour growing tips of medic and lucerne, while in clover they are widely dispersed under the canopy.

Last year, bluegreen aphids caused more damage to lucerne and pasture seedlings than normally experienced in some parts. Research at South Australian Research and Development Institute (SARDI) indicates this may have been caused by a new virulent biotype. Conventional levels of host-plant resistance appear to be broken down in most pasture legumes including lucerne, annual medics and sub-clover. In some cases, plant death has been observed, which is not common for bluegreen aphids. Growers are encouraged to be on the look-out for unusual damage this year and report directly to SARDI Researcher, Alan Humphries at alan.humphries@sa.gov.au.

Spotted alfalfa aphids are a pest of lucerne, legumes and annual medics. Adults 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. Spotted alfalfa aphids are generally found on the underside of leaves and adults may have wings. Early planted pastures are at risk from spotted alfalfa aphids, which are favoured by warm autumns, particularly following an early break.

When considering control options for all aphids it is important to remember that in some cases the whole paddock may not require treatment, as infestations often start at crop edges. If most of the infested plants are along the edges of a crop, a perimeter spray is likely to control the majority of aphids. This approach will also preserve some of the beneficial invertebrate species likely to be present.

CUTWORMS

Agronomist, John Jervois (Tarcutta Rural Supplies), reported that cutworms (Agrotis spp.) have caused severe damage to a several germinating triticale crops near Tarcutta, in the South West Slopes of New South Wales. The damage observed has been quite patchy, with some areas suffering 100% plant death. John said most problems were observed in paddocks that had weeds and stubble over summer, while ‘clean’ paddocks that were cropped in previous years typically had few problems. Prolonged autumn green feed is likely to have allowed caterpillars to develop to a large size by the time crops started to emerge. John says chemical control was required in the worse affected paddocks, which have now been re-sown and appear to be emerging well.

There are several species of cutworm that attack field crops. The caterpillars are hairless, generally plump, greasy in appearance and smooth bodied. Most species have uniform colouring, ranging from pinkish brown to black. They grow to 40-50 mm long and when disturbed curl up and remain stiff as a defensive response. Moths vary in colour from dull brown to black, with wingspans ranging from 30-50 mm. Click here for images of cutworm moths.

Cutworms can have several generations per year and adults emerge in late spring/early summer. The larvae are sporadic pests, causing damage (often patchy) to a wide range of crops and pastures. Just two or three large caterpillars can seriously damage a square metre of crop. They are most damaging in autumn when large caterpillars (>20 mm long) transfer from summer and autumn weeds onto newly emerged seedlings. Young plants are favoured and are more adversely affected than older plants.

Cutworms are often difficult to detect because they tend to feed at night and hide under the soil or litter during the day. Monitoring is best achieved at night and if required cutworms are usually easily controlled with insecticides. Spraying in the evening is likely to be more effective as larvae are emerging to feed and insecticide degradation is minimized.

Agronomist, Bob Ronald (Landmark) has reported leafhoppers (Family: Cicadellidae) causing feeding damage to some early sown wheat paddocks north of Corowa, in the Riverina district of New South Wales. Although it is difficult to estimate leafhopper numbers, Bob says they can be easily observed feeding on plants. Leafhoppers suck sap, resulting in damage of fine pale dots in a patterned ‘wriggly’ or ‘zigzag’ line, which Bob reports was observed within the affected crops.

Adult leafhoppers are approximately 2-3mm in length, and vary in colour depending on species and life stage. They may be yellow, green, brown to dark grey, and are typically elongated and wedge-shaped. Wings are held roof-like over the body at rest. They are very active and jump readily or move sideways when disturbed. Nymphs are usually smaller in size and wingless. There are several species of leafhoppers found in broad-acre crops that are pests of varying degrees. These include the lucerne leafhopper (Austrasca alfalfae), spotted leafhopper (Austroagallia torrida) and the common brown leafhopper (Orosius argentatus). Leafhoppers can be mistaken for aphids.

Leafhoppers attack a variety of crops, including lucerne, legumes and cereals. Numbers tend to build up in spring with peak risk periods in summer and autumn. Most species go through several generations per year and can vector important plant diseases including Australian lucerne yellows disease, cereal chlorotic mottle rhabdovirus and phytoplasma. Leafhoppers attack all crop stages but are particularly damaging to slow growing seedling crops. Well watered, rigorously growing crops can usually tolerate damage. Researcher, Piotr Trebicki (Vic DPI), says leafhoppers are unlikely to cause significant problems in southern areas over the next few months. Piotr suspects numbers will likely decline over winter months and says control is unlikely to be required at this time of year. Leafhoppers can be sampled with a sweep net and/or looking for signs of their distinctive feeding damage.

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 email stuart@cesarconsultants.com.au A free pest identification service is available to all PestFacts subscribers.

Top