Implement pre-sowing control measures in paddocks with stubble pest problems.
Managing slaters, millipedes, and earwigs is not always as straightforward as we’d like it to be.
Management options are limited and poorly understood for this trio of invertebrates, and they must be enacted prior to sowing.
Once the crop has germinated, cultural and chemical control options are further limited.
What’s more, millipedes and slaters are often happy feeding on decaying stubble and organic matter in paddocks. This means they can be present in high numbers without causing crop damage. We do not understand what triggers these species to turn their attention to crop plants in some circumstances. Nor can we predict under what conditions damage is likely to occur.
However, if you have identified paddocks with an ongoing issue with these stubble pests, these are the best-bet pre-sowing control options that can help:
Reducing crop residues
Crop stubble provides a cool, moist habitat that helps invertebrate survival.
With stubble retention practices a mainstay on many farms, slaters, millipedes, and earwigs have become common in broadacre crops.
Managing stubble is likely to be an effective strategy to reduce slaters, millipedes, and earwigs. This may include removal of trash and burning of crop residues to create an environment that is less favourable.
However, note that while some growers have had success managing slaters ahead of canola rotations by burning crop residues, in other cases, crop damage seems to be more pronounced in burnt paddocks. In this situation, it is plausible that slaters that avoid the heat of a burn through harbouring in soil cracks, become more voracious in the absence of stubble and attack emerging plants.
While slaters, millipedes, and earwigs can attack multiple plant species, some crops are more susceptible to damage than others.
Research has shown that when presented with canola, wheat, oat, lucerne, red lentil, chickpea, faba bean, and lupin plants, the black Portuguese millipede (Ommatoiulus moreletii) only damaged canola, lucerne, and lupin. When the pill bug slater (Armadillidium vulgare) was presented with same selection of crops, this species damaged all species except faba beans. Wheat, chickpea and lentil may also be regarded as less susceptible to pill bug damage as there was comparatively little damage compared to lucerne, canola, oat and lupin.
Earwigs can also damage a variety of crops, however canola is particularly susceptible.
When planting canola in slater, millipede and/or earwig problem paddocks, consider a high vigour variety at an increased seeding rate to compensate for damage.
Seed treatment choice will also influence the degree of feeding damage.
cesar has conducted research trials that show fipronil-based seed dressings (which are registered to control redlegged earth mites in canola) can help canola seedlings withstand attack from slaters, millipedes, and earwigs.
However, seed treatments alone will not provide complete protection from these species.
If you do get stuck with millipede, slater, and earwig damage post-emergence, baiting may provide some control.
cesar has recently undertaken laboratory-based microcosm trials with Bayer CropScience looking at methiocarb baits, which are registered in a number of crops to control slugs and snails. Although preliminary, these trials showed methiocarb has efficacy against the pill bug slater, the black Portuguese millipede and the European earwig.
There are no foliar insecticides registered against slaters, millipedes and European earwigs in broadacre crops, and field reports indicate they are relatively unaffected by sprays of both synthetic pyrethroids and organophosphates applied to control other crop establishment pests.
One of the challenges is these species tend to shelter under stubble, rocks and clods of soil, avoiding contact with insecticide sprays.
Using broad-spectrum insecticides will also have negative consequences on beneficial invertebrates that play a role in controlling crop pests.
It is important to always follow label instructions when selecting and applying chemicals, recognising there are different state and territory laws.
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