How to Handle Establishment Pests: Slugs, Earwigs, Slaters, and Crickets

As winter crops are being sown across Victoria and southern New South Wales, it’s time to consider pest management strategies for the early stages of crop establishment. The onset of 2024 has been marked by a warm start to the season and early, widespread rainfall across many regions of south-eastern Australia. Given these conditions, monitoring during the initial phases of crop growth is essential to identify key establishment pests, such as slugs, earwigs, slaters, and black field crickets.

Slugs

In recent years, slug numbers have surged, especially in high rainfall areas (>450 mm), though the uptick in slug populations from previous years may extend the problem to regions not traditionally affected by slug damage. Typically, adult slugs come out of their summer aestivation following autumn rains, which provide them with the perfect conditions to thrive and damage crops during establishment.

Black keeled slug (Milax gagates), photo by Andrew Weeks, Cesar Australia

An integrated management approach is highly encouraged to control slug populations. Monitoring during autumn is key to assessing risk levels, determining the optimal timing and location for baiting, and identifying the specific slug species present. The main pest species of slugs affecting broadacre crops are the black keeled slug (Milax gagates) and the grey field slug (Deroceras reticulatum).   

Earwigs

The European earwig (Forficula auricularia), an invasive species, has established itself across southern, south-eastern, and southwestern regions of Australia. Between March and May, female earwigs disperse into paddocks and establish nests under soil clods.

European earwig (Forficula auricularia), photo by Joseph Berger, Bugwood, CC by 3.0

This pest has a broad appetite, attacking various broadacre and horticultural crops, as well as feeding on both dead and living plant and animal matter. Their feeding habits include leaves and stems, as well as germinating seeds. Canola and certain legume crops are especially vulnerable during establishment, with severe infestations leading to defoliation or complete destruction of young plants.

Monitoring with visual searches or pitfall traps is crucial before and after sowing. Note that not all earwig species are harmful; for example, the native common brown earwig (Labidura truncata) is a beneficial predator.

Slaters

Though slaters have been increasingly reported in recent years, actual crop damage to emerging seedlings is still rare. Even in high numbers, they often prioritize decaying organic matter over crops.

Common slaters found in broadacre crops are the common slater (Porcellio scaber) and the pill bug (Armadillidium vulgare), with the flood bug (Australiodillo bifrons) occasionally causing issues in parts of northern NSW.

Common slater (Porcellio scaber), photo by Josh Douglas

When slaters do damage crops, their feeding leaves behind a distinctive, uneven rasping pattern that can resemble slug or snail damage. They may chew on the tops of emerging cotyledons or crop leaves, sometimes leaving only the seedling stumps. Additional harm includes ring-barking of stems and young branches.

Black field crickets

Black field crickets (Teleogryllus commodus) are on the rise in Victorian cropping regions and urban areas. Monitoring in April and May is crucial, as their numbers are influenced by autumn rainfall.

Black field cricket (Teleogryllus commodus), photo by Andrew Weeks, Cesar Australia

They thrive in Australia, especially in soils prone to cracking or stony terrain, burrowing during dry spells but surfacing after rain. During the day, they hide under loose soil and stones, emerging to feed at night.

They threaten pastures, emerging cereal crops, and various field crops like sunflower, soybean, and pulses. Adult and nymph crickets cause substantial damage to leaves, stems, and pods. In large numbers, black field crickets can thin out seedling crops so severely that resowing may be necessary.

Regularly check establishing crops and pastures in regions vulnerable to crickets to protect your yield by inspecting crops at dusk when the pests are most active. Light traps can be useful for tracking their movements.

Considerations

When it comes to managing these pests, there are a few important factors to keep in mind. Here are some key considerations for evaluating the potential impact of these pest groups on your farm, and how to manage them.

Presence Without Being Pests: Certain species like earwigs and slaters can coexist with crops without causing harm. Certain earwigs act as beneficial predators, controlling pests, while slaters aid in decomposing organic matter. Although they typically don’t harm living plants, they may occasionally feed on emerging crops. The challenge lies in understanding what triggers these species to shift their focus to crop plants in some cases, as well as predicting when and under what conditions damage might occur.

Know your Risk: The susceptibility of broadacre crops to earwigs, slaters, slugs and crickets varies significantly.

Slugs pose a threat to various crops, with canola and wheat seedlings being particularly vulnerable. Earwigs affect broadacre crops like canola and lucerne, while cereals and chickpeas may also suffer damage. Slaters are especially harmful to canola seedlings and can damage wheat, oats, lentils, and pastures in south-eastern Australia. Black field crickets target pastures, emerging cereal crops, and other field crops like sunflower and soybean, with heavier soils posing a higher risk.

The following table, derived from extensive research on crop vulnerability, provides a high-level overview of the risk posed by these the European earwigs, slaters, and millipedes.

Susceptibility of grain crops to feeding damage by the European earwig, black Portuguese millipede and pill bug. Finding adapted from Douglas et al. 2017, Kirkland et al. 2020, and reports to Pestfacts south-eastern.

Identifying the True Culprit: Damage from slaters and earwigs often resembles that caused by slugs and snails, making it difficult to determine which pest is responsible for the harm. Conducting night-time searches with a flashlight can help pinpoint the responsible pest by catching them in the act. This knowledge helps ensure that any control measures you implement are targeted and effective.

Limited Control Options: No foliar insecticides are approved for use against slaters or European earwigs in broadacre crops, and pests like earwigs, slaters, and crickets present unique challenges as they often hide under stubble, rocks, and soil clods, keeping them out of reach of insecticide sprays. Field reports indicate that these pests are largely unaffected by sprays of synthetic pyrethroids and organophosphates used for controlling other crop-establishment pests. Further, reliance on broad-spectrum insecticides can harm beneficial invertebrates that help control crop pests naturally.

Should you find yourself grappling with damage caused by these pests after emergence, baiting techniques could offer a viable solution. Transcend® is registered to control earwigs, slaters, millipedes, snails and slugs in canola. Ensure you’re always following label rates when resorting to chemical control measures.

Research and reports compiled by Cesar Australia suggest fipronil-based seed dressings might mitigate initial damage and bolster the resilience of canola seedlings against attacks from slaters, millipedes, and earwigs. But these treatments lack official registration for this purpose and whilst seed treatments can provide some level of defence, they do not offer full protection against these species.

Know your cultural and biological control options.

Stubble retention often provides favourable habitats for invertebrates like slaters, millipedes, and earwigs. Removing trash, burning residues, or disturbing stubble during summer can effectively reduce slater and earwig populations by disrupting their habitat and exposing them to less favourable conditions.

When dealing with pests like slaters, crickets, or earwigs, consider sowing a vigorous variety at a higher seeding rate. Additionally, support beneficial insect populations like spiders, flatworms, rove beetles, and carabid beetles by adopting sustainable pest management practices, such as consulting the beneficials chemical toxicity table before spraying.

Effective pest management requires ongoing monitoring and a combination of strategies tailored to your specific crops and conditions. Remember, a proactive strategy that integrates various pest management techniques can go a long way in preserving the health and productivity of your broadacre crops.

Acknowledgements

Thanks to Paul Umina for reviewing and contributing to this article.

Cover image: Slug damage in emerging canola. Photo by Julia Severi

What is Pestfacts south-eastern?

PestFacts south-eastern keeps growers and advisers informed about invertebrate pests and beneficials in broadacre crops and pastures during the winter-cropping season in Victoria and southern New South Wales.

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Since 2019 PestFacts south-eastern has been running through IPMforGrains: Best Practice Insect Pest Management, a project delivered by the National Pest Information Network (Cesar Australia, DPIRD, QDAF, NSW DPI, and SARDI). This project aims to provide grain growers and advisors with information on invertebrate grain pest occurrence and equip industry with the knowledge needed to implement integrated pest management practices. This initiative is a GRDC investment and includes in-kind contributions from all project partner organisations.

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