Early season control important in slug battle
Monitoring of slugs by South Australian Research and Development Institute (SARDI) researchers and time-lapse cameras suggest some slugs are starting to emerge from summer refuges, especially the surface active species.
This is supported by anecdotal reports that suggest slugs have been active in the lead-up to the sowing period. Southern Farming Systems chief executive officer Jon Midwood says there are a number of measures growers can take pre, during and post-sowing to control slugs.
Much of the slug damage in the southern region HRZ is caused by two different species – the grey field slug and the black-keeled slug. The grey field slug is mainly surface active, while the black-keeled slug buries itself deep in the soil when the ground dries out, then re-emerges when conditions are moist.
“Because many growers are farming under a no-till or zero-till system, they are hesitant about using cultivation as a pre-seeding control technique,” Mr Midwood said. “However, a selective, light cultivation can break up the grey field slug’s habitat on the soil surface where it lays its eggs. The cultivation will expose and dehydrate the eggs, juvenile and adult slugs and can also improve seedling establishment.”
Mr Midwood stressed the importance of getting baiting right at seeding.
“Spreaders need to be calibrated so there are at least 25 baits per square metre,” he said. “If slug numbers are high then this is the absolute minimum amount.”
The 25 baits/m2 figure means there is an 80 percent chance that a slug will encounter the bait in the first night since it was spread. Growers need to spread baits containing metaldehyde early before there is anything else for slugs to feed on and conditions are still warm.
If baits disappear then rebaiting is required to continue to protect seedlings. For cheap bran-based baits these need to be reapplied more regularly because they break down in moist conditions
A key control option for growers to consider is rolling post-sowing, pre-emergence to help seedling establishment, limit soil clods that provide slug habitat and make it more difficult for slugs to find germinating seed.
Various types of rollers can be used depending on soil conditions. Growers need to aim for a consolidated, fine seedbed.
Later in the season following harvest, it is important for growers to be vigilant in destroying the green bridge of volunteer crops and summer weeds by either spraying or grazing as these can be a habitat for slugs. Reducing stubble loads through burning, baling and cultivation can also help to control slug carryover.
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