Bait snails now before their numbers multiply
Author: Sharon Watt | Date: 13 Apr 2017
As moist autumn conditions trigger snail activity in cropping regions, growers are being encouraged to bait before the pests begin reproducing.
Snails are expected to be a significant problem this year as a result of above-average rainfall and high-yielding crops (and subsequent large stubble loads) in many parts of the southern cropping region in 2016.
Well-timed baiting is essential to ensure an effective kill while snails are feeding and before they commence breeding and laying eggs.
South Australian Research and Development Institute (SARDI*) researcher Helen DeGraaf, whose work is supported by the Grains Research and Development Corporation (GRDC), says now is an opportune time to apply snail baits.
“The cool, damp evenings are activating the snails and there are fewer food sources available,” says Ms DeGraaf, who has recently been monitoring snail activity on Yorke Peninsula.
While on the Peninsula, Ms DeGraaf observed in the mornings both round and conical snails moving up from the ground and attaching to stubble and weeds and hunkering down to wait out the warm day before reactivating at night.
“We observed conical snails mating near Warooka, however no egg-laying was observed. Surface soil appeared too dry to support egg laying, but we would expect eggs to appear soon after the next fall of rain.”
Ms DeGraaf reminds growers to be mindful that mice can interfere with snail baiting and vice versa (snails also eat mouse bait). Each bait is only effective on the target pest.
“Dead snails close to baits (often clustered) indicate that snail bait has reached its target. If bait is disappearing but no dead snails are evident, it’s likely that mice have taken the snail bait.”
Ms DeGraaf says growers must ensure they apply a sufficient amount of snail bait: “Around 25-30 baits per square metre improves your control by increasing the chance a snail will encounter a bait, whilst also accounting for the high populations of hungry snails.”
Snails need to feed and rehydrate before laying eggs. When snails are actively trying to lay eggs, they are less interested in eating the baits, so bait effectiveness is reduced. Additionally, juvenile snails are poorly controlled by baits.
Northern and Yorke Regional Landcare facilitator Michael Richards, who has been leading an innovative project involving the establishment and monitoring of remote video cameras to record the movement and activity of round and conical snails at various locations across SA, agrees that mid-March to early April is an ideal time to bait round snails in southern Australia.
“Higher kill rates are achieved by baiting snails before they reach sexual maturity,” says Mr Richards, whose project is funded by the Australian Government through a Landcare Community Action Grant and Northern and Yorke Regional Baseline Funding, with support from the GRDC, SARDI and the University of South Australia.
“And bait degradation at this time is significantly slower due to lower temperatures and shorter days than in February to early March.”
Mr Richards says applying bait before showers in April is more effective than applying bait after showers, and he recommends baiting mice before snails if high numbers of mice are present.
Snails become active in sandy and loamy soils at 90 percent relative humidity when there is sufficient moisture to change the colour of the soil surface, according to Mr Richards’ observations.
“In heavier soils, round snails become active during showers, and will begin moving again during periods of 90% relative humidity. In sandy and loamy soils, round snails will move from two to four metres when there are at least five hours above 90% relative humidity. After 10 millimetres of rain, round snails will move up to eight metres in sandy and loamy soils.”
Mr Richards says conical snails are more staggered in their movement, with a percentage of conical snails with similar activity to round snails. “The remainder of conical snails become active later in the season. Several bait applications are often needed from mid-March to mid-April to significantly lower conical snail populations.”
Research by Ms DeGraaf, undertaken as part of a new GRDC-supported project across the southern and western cropping regions, has found that snail albumen glands (their reproductive organs) are increasing in size in late March and early April, which corresponds with higher moisture and dewier conditions. This indicates that adults are starting to prepare for egg production, supporting the recommendation to bait now.
The three-year project, which began last year, will develop region-specific knowledge for growers to assist in implementing snail control strategies based on local conditions. The focus of the research being carried out by SARDI and the Department of Agriculture and Food, Western Australia, is on the ecology, behaviour and biology of the most threatening snail and slug species in each region.
Meanwhile more information on snail control can be found in the GRDC Snail Management Fact Sheet and the GRDC Snail Identification and Control Back Packet Guide. A GRDC Snail Bait Application Fact Sheet is available for viewing and downloading, and a GRDC Update paper on insights from recent research is also available.
* SARDI is a division of Primary Industries and Regions South Australian (PIRSA)
Rob Johnson, Communications Adviser, SARDI
0423 292 867
Sharon Watt, Porter Novelli