How do I manage pests in a stubble-retained system

Pests such as mice, snails and slugs, earwigs, millipedes and other invertebrate species love stubble. Stubble retention provides food, shelter from predators and a microclimate away from harsh extremes. To control pests, control their sources of food and shelter.

Canola in the high rainfall zone is especially vulnerable to pest damage.

Integrated pest management will achieve the best control. Regular paddock monitoring is essential for a proactive approach to pest and insect management. Strategic tillage and burning are still valid management options to reduce pest numbers, but must be done correctly. Know the susceptibility of different crops to the range of pests that can build up in stubbles and manage paddocks accordingly.

Mice

Photo of a mouse in canola stubble
Mice are now causing issues in different crop types like canola. Source: GRDC.

Historically, cultivation for weed control meant mice populations had to survive periods with a reduced food supply. Mice are now causing issues at different times of crop growth (tillering and head emergence), in different crop types like canola, and in regions that historically did not have issues. They have also become more of an annual, rather than a cyclical, problem.

Monitor mice numbers prior to sowing (by looking for burrows or by using chew cards) to identify areas on the farm that are most problematic. Management options include:

  • Paddock and farm hygiene are important to keep numbers down, including access to stored grain
  • Reduce grain losses at harvest
  • Graze stubble with livestock to reduce grain and stubbles, which will reduce both food and favourable environmental conditions
  • Spray summer weeds and self‐sown cereals to reduce feed sources over summer and early autumn
  • Windrows or chaff dumps may concentrate mice populations when they remain moist over summer, perimeter baiting should be considered before burning

During plague conditions other agronomic practices may be required to increase crop establishment such as:

  • tillage before sowing
  • timely burning of windrows to maximise temperatures
  • burning stubble/whole paddock burn
  • sowing at the maximum depth
  • increasing seeding rate
  • removing furrows after seeding by tillage/prickle chaining
  • perimeter baiting or whole paddock baiting six weeks prior to seeding and no later than 24 hours after seeding

For more information see the GRDC page: Mouse control is now a year-round activity.

Snails and slugs

Photo of conical snails on stubble
Conical snails.Source: GRDC.

Snails and slugs have the potential to affect crops at all stages (initial germination, development, maturity and grain development), with snails also having the potential to contaminate grain at harvest.

Different species have different movement patterns, habitats and preferred food sources. Understanding what snail and/or slug species are present and their behaviour is critical to selecting the most effective control methods.

The key factors to consider when managing snails and slugs include: paddock history, soil type, environment, weather conditions, existing stubble, stubble management, and crop management including time of sowing, seed source and potential seeding treatments.

Monitoring activity and controlling before mating and egg laying are integral to minimising numbers. The best time to monitor snails is when they are on the move, specifically when relative humidity levels are up around 90 per cent such as on dewy mornings and evenings or during showers. The key monitoring periods are pre-sowing, in-crop, spring and post-harvest.

A rule of thumb is that grain contamination at harvest will be likely if snail numbers are above 20/m2 in cereals and 5/m2 in pulses and canola, be prepared to deal with.

Key points for controlling snails:

  • Combining cultural and chemical methods will provide optimal snail control
  • Controlling snails before egg laying commences is essential for successful integrated control
  • Cultural control methods including cabling, rolling, slashing and grazing
  • Strategic burning remains the most effective method of pre‐breeding snail control, provided that a hot, even burn is achieved
  • There are currently no means to control juvenile snails (less than 7 mm) after sowing – the key is to start baiting before snails lay eggs
  • Stop baiting eight weeks before harvest to avoid bait contamination in grain and only use registered products

Snails love summer weeds as they provide shelter, moisture and food through the summer. Controlling summer weeds removes an important source of moisture. Snail management using several practices well ahead of crop establishment, over the summer period is vital especially as limited control methods are available following crop seeding and establishment.

Research is continuing to understand the biology of snails and aims to identify environmental factors that lead to snail activity and the optimum timings for bait application.

Slugs are common in the high rainfall zone and damage emerging crops, particularly canola.

For more information see the GRDC publications:

Earwigs, millipedes and slaters

Earwig damage mostly occurs in high rainfall regions and there has been little research in cropping situations. Earwigs mainly attack canola but have been known to attack cereals, lupins and some legumes. There are anecdotal indications that bean stubbles increase earwig abundance. Earwig damage looks similar to slug damage.

Millipedes are regularly present but crop damage is rare. Most reports of damage to crops have been in medium or high rainfall regions. Most incidents of crop damage have been related to:

  • High stubble loads, greater than 5t/ha. As high stubble levels are depleted the large populations of millipedes that have fed on the stubble then seek a new food source.
  • Young canola plants
  • Heavy soils

Slaters have been observed causing damage to canola seedlings, wheat, lentils, lucerne and chickpea crops.

Monitoring for invertebrates is difficult and high numbers do not necessarily translate into damage. The only threshold is at 8/m2 for earwigs. There are no registered chemicals for control in broadacre cropping.

Manage invertebrates by cultivation, removing summer weeds and reducing stubble residue through burning, incorporation or grazing. Windrow burning may reduce millipede populations and strategies that increase emergence, such as higher seeding rate, can offset any damage caused.

More Information

Farming Systems Groups