Time to put brakes on slugs and snails

Wimmera grain growers have been urged to monitor and manage slug and snail populations during a recent series of Agriculture Victoria-led presentations by crop pest specialist Dr Michael Nash.

Dr Nash advised growers with snail issues to use cultural methods as a first step in controlling white snails.

“You can kill over 90 per cent of snails by knocking them off stubble,” he said.

“Days with temperatures above 35 degrees are ideal.”

Dr Nash said that snail numbers tend to increase in seasons preceded by a wet autumn and winter.

“Summer rainfall is not a good predictor of snail numbers,” he said.

“Late March is generally the best time for baiting snails in the Wimmera and sometimes you need a follow-up application in April with a more expensive product.”

According to Dr Nash, cheap bran-based products quickly stop working after rain, while small sized pellets will also have much reduced efficacy.

“Baiting in summer in the Wimmera can be very unreliable for a number of reasons, including high temperatures,” he said.

While research has found that 30 to 40 pellets per square metre is ideal for snail baiting, it’s also important that enough active ingredient is present to ensure snails receive an adequate dose. Applied bait can quickly run out where snail populations are dense, leading to poor control.

Dr Nash said that growers with slug issues should use a good quality product at a low rate if dry sowing canola.

“Be aware that not all slugs are pests; the striped slug does not damage canola, so there is no need to control it,” he said.

“Slug pests differ from snails in that you do not need to kill all the slugs; you just need to protect the crop for the first four to six weeks.”

A key learning for farmers at the slug and snail management workshops was that burning stubble would not reduce black keeled slug numbers as they actively burrow into the soil, becoming active after 75 to 100 millimetres of rain.

Black keeled slugs are particularly damaging to canola and can also damage cereals.

Dr Nash said a certain percentage of the slug population will be active each year so it was a good idea to bait annually.

He said that insecticides, including those used in seed dressings, can make slug problems worse, as they can impact populations of beetles that feed on slugs. Metaldehyde bait however, does not affect beetles.

While tiles or mats can be used to monitor slug and snail populations, in future, self-powered monitoring devices that provide population data through smart phones will be available.

The snail and slug management presentations were supported by the Grains Research and Development Corporation and Agriculture Victoria.

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