PestFacts 10 April 2025
Kicking off the 2025 PestFacts SA season
As the new growing season approaches, be aware for early pest activity in crops and pastures. South Australia's dry 2024 likely reduced many pest populations, but late-season moisture and volunteer crop growth could create favourable conditions for resurgence.
Snails have been kept in check by the dry weather, providing better than usual conditions for early control before they lay eggs. Moisture from light rain and dewy mornings will increase overnight snail movement, which means growers should be ready to bait at any time.
While the green bridge (which harbors pests such as aphids and various insect larvae) hasn’t been as strong in the dry conditions, any surviving pests could quickly spread to nearby crops as the season progresses. This makes it crucial for growers to monitor fields closely and manage any potential pest threats before they increase.
In this issue, we’ll cover the key pests to watch out for, provide insights from recent field observations, and share management strategies to help you stay ahead of the curve this season. Stay tuned for more updates and don't forget to report any unusual pest activity. Your observations help build a clearer picture of pest trends across South Australia, allowing for better-informed pest management decisions.
Wishing you a productive and pest-free season ahead!
Snail populations and early season control
By Dr Kym Perry, University of Adelaide
Email: kym.perry@adelaide.edu.au
What’s happening with snail populations this year?
Extremely dry conditions in many parts of South Australia over the past year have had one positive effect: snail populations have been kept in check by the weather.
It is likely that the lack of season-breaking rains in early 2024 also limited snail breeding, which typically commences from early autumn and lasts until at least mid-winter.
Similarly, dry conditions in the spring and summer 2024–25 will have caused higher than usual levels of mortality, particularly of snails resting in exposed areas and in districts that experienced any heatwaves. Exposure of snails to temperatures of 60oC kills them instantly, and on a sunny 40oC day, ground level temperatures can exceed 70oC. Finally, a relatively low abundance of green summer weeds will also have reduced summer survival.
Can I take a rest from snail control?
While snail populations are starting from a lower base in 2025 compared to most other years, does this mean there is a lesser need for snail control operations? The short answer is that lower snail numbers is good news for growers.
However, in areas where pest snail infestations occur, there are generally many more snails present than it can appear at first glance. This is particularly true for conical snails (Cochlicella acuta) and small-pointed snails (C. barbara), which prefer to shelter underneath refuges (such as rocks and logs) and inside plants (such as grassy tussocks or Lincoln weeds), over resting sites above ground level.
When the weather turns favourable again for snails (when it rains), it is often surprising how many snails suddenly appear, seemingly out of nowhere. These snails were present all along but hidden in cryptic refuges. Know where to look!
Snail populations can bounce back quickly when conditions are moist and favourable. Therefore, taking every opportunity to control snails prior to egg laying remains important. Don’t let snails off the hook. Snail control should be easier and more effective this autumn given lower starting numbers.
When to apply snail bait for maximum return on investment
The best timing to start snail baiting is just after snails first become active after summer aestivation (dormancy, induced by dry hot and weather). This is around the end of summer and early autumn.
The ‘sweet spot’ timing to commence baiting is typically sometime around mid-March to mid-April, depending on local weather and farm conditions. Increased moisture causes snails to start moving in search of food. This typically occurs overnight on dews and light showers and often goes unnoticed.
These snail movements provide early baiting opportunities that can be very effective. This is because snails are extremely hungry after summer dormancy, and a lack of alternative food sources (residues, crop seedlings) increases rates of pellet encounter by snails. At this time, snails spend several weeks feeding and maturing their reproductive organs in preparation to start breeding and laying eggs.
The early autumn pre-sowing period is a great time to bait snails. At this time, snails move mostly when ground humidity exceeds about 95%, which can occur on overnight dews or very light rain showers (less than 2 mm). A well-timed bait application when snails are hungry can achieve high levels of control. Kill as many as you can before they start laying eggs.
See Nail the Snails for guidelines for baiting, including a product selection guide.
Key baiting tips:
- Choose your preferred bait product.
- Broadcast pellets evenly.
Use a spreader calibrated for your chosen product. - Apply bait at the right time.
Before snails lay eggs, and when snails are expected to move across the soil surface. Aim to apply to when ground relative humidity will exceed 95% (ideally close to 100%). - Apply bait at the right rate.
Apply and re-apply bait at registered rates to achieve sufficient bait points, ideally at least 30 bait points per square metre.
New camera network provides snail movement alerts for farmers
For the first time, growers can now receive updates on snail activity in near real time to help with baiting decisions and timing in autumn 2025.
A network of 6 ‘experimental’ S3 sentinel snail cameras has been deployed, with three units in SA and three in WA. The three South Australian cameras are located on southern Yorke Peninsula, near Watson Beach and Warooka, and on Eyre Peninsula at Coulta.
This is part of a GRDC invested project 'More effective control of pest snails in Australian grains crops', led by Dr Kym Perry from University of Adelaide, and in collaboration with SARDI, UniSA, CSIRO, DPIRD WA, and Data Effects.
For regular updates on snail activity, follow Dr Kym Perry on social media at:
- X (Twitter): @x_slimeminister
- Instagram: @the_slimeminister
Control pest movement by managing the green bridge
By Precious Kudzaishe Mavende, PhD candidate, University of Adelaide
Email: kudzaishe.mavende@adelaide.edu.au
What is the green bridge?
A 'green bridge' is any kind of unwanted vegetation, like weeds or leftover plants, that can help pests survive between crop seasons. These plants act as a 'bridge' for pests, like insects or diseases, allowing them to stick around and move to the next crop when it's time to plant.
Green bridge management
The management focusses on controlling the vegetation, such as weeds or volunteer plants, that might act as a refuge for pests when there are no main crops in the field.
Effective green bridge management involves practices like:
- Weed control
Removing or managing weeds and unwanted vegetation that can harbor pests. Control weeds early, ideally at least four weeks before sowing. - Cover crops
Using plants that aren't attractive to pests, so they don't provide a habitat for them. - Crop rotation
Changing the types of crops planted to disrupt pest life cycles and reduce the chance of pests using the green bridge. - Timely destruction of plant
Destroying any leftover crop residue or volunteer plants before new crops are planted.
Are green bridges supporting natural enemies over summer?
Green bridge can also harbour a range of beneficial insects, including ladybird beetles, hoverflies and parasitoid wasps that build up on pest populations. Identify plants that encourage the survival of beneficials and consider reducing herbicide application on green bridges to support beneficial insects’ populations and naturally control pests in crops.
What is an aphid parasitoid?
Aphid parasitoid wasps are up to 4 mm long and deposit an egg within an aphid. As the parasitoid larva develops, it consumes the aphid from within. When the larva matures, it spins a cocoon while the aphid dies and the aphid body changes into a swollen tan or golden husk known as a 'mummy'. This husk protects the parasitoid larva during development. When a winged adult parasitoid is ready to emerge, it will cut a hole in the husk and exit the mummy. This development process can take up to 15 days depending on temperature and the parasitoid species.
We know that aphids can survive on various plants, including weeds in the absence of crops, but little is known about the survival of parasitoid wasps over summer. Through the University of Adelaide, my project aims to get an insight into the survival strategy of the aphid parasitoids.
Since the beginning of this year, I have set up surveillance units of suction traps, yellow sticky traps and yellow pan traps in 4 canola paddocks scattered between the north (Turretfield and Pinery) and south (Bowhill and Keith) in some canola growing regions of South Australia. With the active participation of our local growers, the traps are changed regularly, brought back to the Waite campus laboratory and screened for the presence of aphids and parasitoids.
Green-bridge sampling
With the financial support from SAGIT, I am on the road, sampling different actively growing weed plants along the roadside and some horticultural crops for aphids and their parasitoids. The plants are placed in sealed rearing 'eclosion' boxes that have a single exit passageway leading to a tube with a sample preservative liquid. All rearing boxes are put in a room with 24-hour lighting and left for three weeks to allow for the development of parasitoids on the plants.
While it has been a slow start in both aphid and parasitoid recordings because of the dry spell, it will be interesting to see what we observe in the coming months leading to the 2025 canola growing season, particularly with the regeneration of weeds. To date, we have collected similar weed composition such as caltrop, common sow thistle, potato weed, skeleton weed and wild radish during our surveillance trips. In the last week, we are starting to see more general insect activity within the environment influenced by the light rains enhancing weed growth.
Get involved
My project aims to:
- Recommend a standardised method for monitoring aphid parasitoids in grain crops to assist with informative decision making for aphid management.
- Investigate the over summering strategies of parasitoids in South Australian environmental conditions.
- Study the response of parasitoids to different aphids feeding on various plant species.
Sampling of weeds will continue throughout the year. I need your help to keep an eye out for weeds with aphids and mummies. If spotted, please:
Weeds
- Take a good photo of the weed sample and surroundings.
- Send the photos with gps coordinates to either:
- text 0414 020 006
- X (Twitter): simply hashtag #precious_wasps or follow @precious_wasps
- LinkedIn: Kudzaishe Precious Mavende
Mummied aphid
- Take a few good pictures of the plant.
- Carefully collect the plant material where the mummy is attached and place in a vial with a small hole or cover the opening with a mesh (this will allow for airflow but prevent the escape of the parasitoid when it emerges).
- Attach the completed form to the sample and send via express mail to:
Kudzaishe Precious
The University of Adelaide - Waite Campus
Waite Building, 1st Floor- East Wing, Office E110
Waite Road
Urrbrae SA 5064
Psocids in grain sheds: Moisture-linked pests
Recently, we received a report from northern Adelaide regarding psocids in a grain storage shed.
Psocids (Psocoptera spp.), commonly known as booklice, are tiny (up to 1 mm), soft-bodied, opaque, pale insects with long, hair-like antennae. Liposcelis spp. are wingless, while some other species possess wings.
These scavengers thrive in grain storage facilities, mills, processing plants, and homes, particularly in damp environments. They are often the first to reappear after fumigation and can be found in large numbers, even in otherwise clean premises. Psocids frequently appear as a 'moving carpet of dust' on grain or storage structures. As secondary pests, they feed on damaged grain and moulds.
In Australia, there are three main species of psocids, often occurring in mixed populations – see Stored grain pests identification.
Lifecycle and conditions
Psocids thrive in warm, humid conditions, with optimal growth at 25°C and 75% relative humidity – though they can survive in temperatures ranging from 18°C to 36°C with at least 60% humidity.
Their life cycle lasts about 21 days, with eggs laid on the grain surface, hatching into nymphs that moult into adults. Nymphs resemble adults but are smaller and paler. Adults are long-lived, actively feed, and move quickly.
Control and management
Effective management requires reducing humidity below 60% to prevent infestations – see Psocids, managing on farm grain storage.
Additionally, standard phosphine fumigation must be highly effective to ensure proper control of these pests.
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:
Maryam Ehsangar
Phone: 0448 010 339
Email: maryam.ehsangar@sa.gov.au
Maarten van Helden:
Phone: 0481 544 429
Email: maarten.vanhelden@sa.gov.au