PestFacts 5 May 2023
Black field crickets
Black field crickets (Teleogryllus commodus) have been observed in higher than usual numbers in cropping and pasture paddocks around parts of South Australia this autumn. Large numbers have been reported in the South-East feeding on sub clover burrs, cereal seeds, and the tops of cereal seedlings. Canola seeds were not fed on. SARDI Entomology have also observed crickets in paddocks with lentil and cereal stubble near Cummins and Yeelanna on the lower Eyre Peninsula. Crickets were moving in and out of soil cracks during the day, and loud chirping could be heard.
Cricket populations are largely determined by weather conditions and may have benefited from wet and humid conditions during last spring following above average rainfall.
Black field crickets are omnivorous and can feed on pastures, lucerne, field crops including cereals and pulses, and horticultural crops. Young cereals and pastures are most susceptible to feeding damage. Adults and late-stage nymphs feed on the leaves and stems of seedlings, on flowers and immature seeds.
Identifying black field crickets
Adults are 25 mm long, brown-black in colour with two pairs of wings, long thin antennae, three pairs of legs and a pair of projections (cerci) at the end of the abdomen. Their hind legs are spined and modified for jumping. Early-stage nymphs are smaller, wingless, and sometimes have a white band across their back. Late-stage nymphs are uniformly brown-black and have wing pads.
Monitoring and control
Monitor establishing crops and pastures on heavier clay soils. Place hessian bags or similar at regular intervals across the paddock and check numbers underneath regularly. Light traps or night inspections using a torch can also be used to monitor cricket activity.
Baiting with maldison-treated cereal grain (whole or coarsely ground) is the preferred control option and is most effective when there are few alternative food sources available (i.e. when pasture is dry). Carefully follow product label directions, mix chemical thoroughly with grain and apply at a rate of 10 kg seed per hectare.
Autumn slug baiting for integrated control
Now is the time to monitor paddocks for slug activity. Slug baiting in infested areas should occur at or immediately after sowing, before seedling emergence, to protect seeds and seedlings.
Slug biology and damage
The black-keeled slug (Milax gagates) and the grey field slug (Deroceras reticulatum) are the two major slug pests of crops and pastures in southern Australia. Canola is especially susceptible to damage.
Other species that may be present include brown field slug (most likely Deroceras invadens or D. laeve; some taxonomic uncertainty exists) and striped slug (Lehmannia nyctelia).
Slugs are generally more problematic in higher rainfall climates (more than 500 millimetres) and seasons, and in paddocks with heavy soils that retain moisture or crack. Slugs feed on crops at all stages but cause the most damage to seedlings.
Grey field slugs feed mostly on the soil surface, feeding on plants at ground level and consuming cotyledons, leaves and stems, sometimes severing seedlings. Black-keeled slugs feed similarly at the soil surface but also burrow below ground to feed on germinating seeds.
Slugs are mostly inactive during summer. The black-keeled slug burrows to depths of 20 centimetres or more to survive the heat, whereas the grey field slug seeks refuge under rocks, logs or summer weeds and debris, or by moving into cracks in the soil. Soil-penetrating rainfall and cooler temperatures increase slug activity on the soil surface in autumn and winter.
Monitoring and baiting slugs
Monitor slug activity using surface refuges or bait lines. Focus monitoring in areas with a history of slug problems and/or moisture-retaining soils.
For refuge-based monitoring, silver slug mats are more attractive to slugs than tiles, with more than four times more slugs captured according to research.
Place refuges along several rows (i.e. transects) in representative paddock areas, with pellets underneath each refuge, and check for slugs after a few days. Slug numbers can vary greatly between transects.
Bait lines are a useful alternative to refuges. Place a line of pellets (e.g. 100 metres in length) along a seeding furrow and check for dead slugs after a few days. Do this in several furrows. Bait lines are easy to apply and monitor but may need re-application after 2 to 3 weeks or when pellets break down.
The presence of dead slugs under refuges or in bait lines indicates slugs are actively feeding, and bait should be applied. After application, monitor and re-apply as necessary. For information on bait products, refer to the snail and slug baiting guidelines ().
Integrated control
Baiting slugs at sowing is part of year-round integrated slug management, together with cultural controls. Slug populations can be reduced by fine tillage followed by rolling.
Slugs can be managed in no-till systems by well-timed baiting at sowing in combination with agronomic practices to achieve rapid crop establishment. These include early sowing before slugs are active, the use of hybrid rather than open-pollinated seed varieties, rolling to compact the seed bed and restrict slug movement, and weed management. For further slug management advice, see Paddock practices: Be on alert for slugs in the HRZ.
Paddock trial demonstrates importance of monitoring
European earwig (Forficulina auricularia), black Portuguese millipede (Ommatoiulus moreletii) and slaters (typically the pill bug and common rough woodlouse, but also sometimes Australiodillo bifrons) are often accused of lopping seedlings, though they mainly feed on decaying organic matter and even can be useful predators (e.g. earwigs eating aphids).
Stubble retention practices are favouring these species by creating moist refuge habitats and providing food. It is difficult to predict the extent to which they will feed on live crop plants. Trials in greenhouse situations (see Crop seedling susceptibility to Armadillidium vulgare (Isopoda: Armadillidiidae) and Ommatoiulus moreletii (Diplopoda: Iulidae)) confirm that these species can feed on some plants, but does this occur in a real cropping situation?
Reports of these invertebrates causing damage to emerging crops can be questionable. Observing crop damage and simultaneously seeing these invertebrates does not necessarily mean they are the cause. Instead, they may be feeding on already damaged plants. These species are mainly active at night and sometimes high populations go unnoticed, so catching them red-handed is essential.
In the South Australian Grain Industry Trust (SAGIT) funded project 'Caught red-handed', SARDI Entomology recorded feeding activity on seedlings using infrared night vision cameras in 2021 and 2022. Seedlings were set up in front of cameras in 6 paddocks before and after the crop was sown. Pitfall trapping was used to have a second observation method for ground dwelling invertebrates in the same area. This project gave good insight into the culprits:
Big differences between paddocks
Not surprisingly, the invertebrate communities were very different among paddocks, with more than 25 species recorded on nearly every site. Earwigs were only present in the higher rainfall areas (more than 400 mm), whereas millipedes are present everywhere but in variable numbers. Slaters (in this case Australiodillo bifrons) were present in high numbers in only one paddock.
Other species observed included:
- ants
- aphids
- weevils
- other beetles
- snails
- spiders
- mice.
The main species feeding is European earwig
Earwigs were the main invertebrate feeding on seedlings, with a high feeding ratio. Feeding was observed in 63% of individual observations.
Black Portuguese millipedes were rarely damaging seedlings, even when present in high numbers, with only one paddock having significant numbers and 23% feeding events, while others were below 5%. Millipedes are mostly detritivores, eating dead plant matter, and not attacking healthy living plants. The slaters were rarely seen damaging seedlings (less than 3% of observations in only one paddock).
Other culprits unveiled
Our images revealed other major culprits including red legged earth mites and weevils. Weevils are rarely reported for seedling damage, but they were present in higher numbers than expected in 5 of the 6 paddocks and were seen feeding on crops in up to 35% of all observations. Weevils may largely go unnoticed because of their near perfect camouflage.
Snails and slugs were not present in high numbers in any paddocks.
Mice were seen and our observations confirmed they are good grazers, wiping out some seedling trays in a few hours.
Several beneficial species were observed, mainly ants, carabid beetles and spiders, with large differences between paddocks.
Pest preferences vary
Of the crops tested in this trial, faba beans were a preferred food source for earwigs, millipedes, and weevils. Weevils also feasted on the canola. Red legged earth mites largely preferred vetch but also fed on canola and wheat.
This trial confirms that earwigs, when present, are the most likely to damage seedlings. Millipedes and slaters might often be accused unfairly, while weevils are more important than previously thought. Beneficial invertebrates were present in all paddocks, so think twice before applying insecticides pre-sowing.
This two-year project looked at a limited number of paddocks, which means we might have missed certain species such as snails and slugs, or the pill bug, Armadillidium vulgare. We also might not have been in a situation that would induce plant feeding in species that would normally be detritivores.
If you have crop damage, a late evening observation (in the dark) is necessary to determine which species are involved.
Further research is required to determine the impact of soil type, preceding crop, chemical history, surrounding landscape, weather conditions and weed communities on invertebrate populations and their appetite for crops.
More information
Predicting pest issues from common and curious pests of crop seedlings in south-eastern Australia
Identifying and monitoring stubble pests
Increased stubble retention practices have increased the habitat for several invertebrates that can damage broadacre crops. Many of these species mostly feed on decaying plant matter, and large numbers don't always mean they will feed on crops. Removing refuges pre-sowing, understanding the paddock history and monitoring are the best ways to understand and tackle these pests.
Species to look out for during emergence include:
European earwig
The European earwig (Forficulina auricularia) is a common species throughout South Australia, often occurring in large groups. European earwigs are 12 to 24 mm long, have a dark and relatively uniform body colour with yellowish shoulders, legs and pincers.
Native earwigs are also widespread throughout Australia, usually seen individually or in low numbers and are not typically considered pests. Be sure to identify the earwigs on your property as some native earwigs such as the common brown earwig (Labidura truncata) predate on pest insect species. A useful identification key can be found in the I Spy - Identification manual and education resource.
Weevils
Mandalotus weevils (Mandalotus spp.) are a group of native Australian weevils, with at least 10 species known to feed on crops in parts of south-eastern Australia. Adults are 3 to 5 mm long and emerge onto the soil surface in late autumn. They are often difficult to find, so search at night using a torch, or during the day in the top 1 cm of soil at the base of weeds or damaged seedlings. Adults lop stems, cotyledons or seedlings.
In canola, check areas with a history of Mandalotus damage one week after emergence. If needed, an insecticidal spot treatment to control adults is the only management option. See Mandalotus weevils in canola () for more information.
The vegetable weevil (Listroderes difficilis) is a sporadic pest widespread in cropping areas. Adults and larvae feed on foliage at night in early winter. Adults are 8 mm long with grey-brown bodies, a prominent weevil snout and a distinctive pale-coloured V on their back. Larvae are legless, yellow to green in colour with an orange-brown head. Check emerging canola crops for damage and weevils along crop edges or near areas with host weeds, particularly capeweed.
Black Portuguese millipede
Black Portuguese millipedes (Ommatoiulus moreletii) are common Australia-wide, and are typically a nuisance pest in houses. They have a smooth, cylindrical body. Adults are 30 to 45 mm long, dark grey to black in colour and have 2 pairs of legs on most body segments. Juveniles are light brown with a darker stripe along each side of their body.
There are many native species of millipede that aren't regularly seen, but if the millipede you find is very bumpy looking it is likely to be a native.
Slaters
Several species of slaters are found in cropping areas, including:
- the common rough woodlouse (Porcellio scaber)
- the pill bug (Armadilidium vulgare)
- the flood bug (Australiodillo bifrons).
Slaters are land crustaceans that have oval-shaped bodies, often flattened. Most slaters are about 6-12 mm in length and dark grey in colour, but mottled colours are common. Their bodies have 14 segments, 7 pairs of legs and two pairs of antennae, though the second pair is small and hard to see.
The pill bug rolls up into a ball when disturbed, but the rough woodlouse and the flood bug cannot.
Monitoring and control
Monitor crops immediately after sowing by using a torch to scope out their activity at night when they are feeding. During the day these species appear absent but may be found under rocks, or hiding in stubble residue, wood or in the soil. They are more likely to be in paddocks with heavier soil types and paddocks with greater amounts of refuges.
Reducing stubble retention and other refuge spaces is the most effective way of managing stubble pests. There are no foliar insecticides registered for earwigs, millipedes or slaters in broadacre crops.
Predatory beetles such as carabid beetles in high numbers may help control earwigs.
More information
Play your part to protect our grains industry
Early detection and reporting are critical to successfully stopping exotic pests from getting into Australia. Khapra beetle (Trogoderma granarium) is the most concerning exotic plant pest for the grains industry, and we can all play a part in keeping it out of Australia.
In warm conditions, Khapra beetles multiply quickly, causing severe damage to stored grain. Other products can also be contaminated by these beetles that shed larval skins and hairs, which can pose health risks and are very difficult to remove from storage facilities and transport vessels. South Australia's surveillance and rapid response programs delivered by the Department of Primary Industries and Regions (PIRSA) have been crucial in timely detection and responses to reported pest incursions. This has been crucial in keeping our state and country free of these pests to-date. Our robust biosecurity system relies on a collaborative approach between government, industry and the community.
Biosecurity is everyone's responsibility, whether you are a grower, grain handler, food or feed manufacturer, transporter, tourist, or member of the community.
Grain growers can play their part by:
- being familiar with common grain pests to identify anything unusual, and calling the Exotic Plant Pest Hotline 1800 084 881 if you suspect an exotic pest
- frequent inspections and monitoring at grain storage sites and facilities to detect the presence of new pests and unusual damage
- maintaining good hygiene at storage facilities, including the timely clean-up of spillages
- being aware of machinery and equipment (containers) that have been linked to international movements that may provide a pathway for infection
- when transporting grain
- avoiding overloading that may lead to spillage
- making sure trailers are clean and any leftover grain is disposed of properly
- talking to others in the industry about hitchhiker pests to raise awareness.
Grains Farm Biosecurity Program (GFBP)
Launched in 2007, the GFBP is managed by Plant Health Australia and funded by growers through Grain Producers Australia, together with the South Australian, New South Wales, Queensland, Victorian and Western Australian governments. The program helps develop and deliver materials to raise awareness among growers, consultants and other industry stakeholders.
Grains Farm Biosecurity Program website contains fact sheets, videos, how-to guides, online training and strategies to help manage on-farm biosecurity risks.
Contact
If you have questions about grains biosecurity or the programs being run, contact:
Shafiya Hussein – South Australian Grains Biosecurity Officer
Phone: 0437 723 295
Email: shafiya.hussein@sa.gov.au
Report to PestFacts
The PestFacts SA team always wants to know what invertebrates you find in your crops and pastures, whether it is a pest, beneficial or unknown – even the usual pests.
Please send your reports or identification requests via the PestFacts map.
Alternatively, please contact:
Rebecca Hamdorf
Phone: 0429 547 413
Email: rebecca.hamdorf@sa.gov.au
Maarten van Helden:
Phone: 0481 544 429
Email: maarten.vanhelden@sa.gov.au
The latest information for growers and advisors on the activity and management of pests in all broadacre crops during the winter growing season.
