Grains Research and Development

Date: 01.02.2002

B&B for Snails

BASHING stubble and early baiting should be the focus of summer and autumn snai management. Both actions will help reduce snail numbers from last year and egg laying this year.

Traditionally, snail control methods have been stubble management in the summer and baiting in the winter. Stubble management continues to be crucial, but results from research by the SA Research and Development Institute (SARD!) show that early baiting after the opening rains in March-April gives a good level of snail kill before egg laying commences. "Each snail is hermaphrodite, both male and female. As each one can lay an average of 400 eggs, preventing egg laying is a key to reducing snail populations," said Megan Leyson, the newly appointed entomologist at SARD!, who will be leading the snail research project.

Stubble management

On average, stubble management results in a 50 per cent reduction in the live snail population, with the greatest impact on round snails. It is sometimes less effective against conicals as they can escape the summer heat by hiding under rocks, etc. Cabling is becoming a popular method of removing snails from stubble and led to reductions of up to 70 per cent last year.

Cabling is rather more aggressive than rubber tyre rolling and results in snails being knocked from their perches, as well as laying much of the stubble flat. However, cabling is not su itable when soils are susceptible to wind erosion. Cabling is carried out using a 3- 5 cm diameter cable, often an old punt cable, strung between two tractors, which are driven about 300 m apart. The cable is pulled through the stubble on very hot days knocking snails to the ground.

Where a heavy layer of straw insulates the ground, cabling is unsuitable, as it relies on the snails hitting the hot soil and dehydrating as they move back to their perches. Allowing snails a day to return to their perches and then repeating the cabling operation is especially effective as the snails rapidly burn up their stores of water and food. Another advantage of cabling is that it turns rocks, exposing the conicals that may be sheltering beneath.

Last year Bill Long, Yorke Peninsula agronomist and farmer, had excellent success with cabling on his property. "One of the big benefits of cabling over rolling is that large areas can be covered rapidly, a 50-hectare paddock is cabled in about 20 minutes. "At these speeds we have the capacity to cable a paddock several times, which results in an excellent level of snail mortality." If stubble is going to be rolled or slashed, growers should wait until later in the day when soil and air temperatures are higher.

Ideally, air temperatures should be at least 35"C. Cabling can be carried out at slightly cooler temperatures.

Burning

Mr Long has also been looking at the impact of burning stubble on snail mortality.

A good even burn is required to kill snails, with white snails being more susceptible than conical snails as these can bury into the soil or be protected under rocks.

A hot burn early in the season may not be necessary, especially in areas with a high erosion risk, as the use of a cooler burn and tire harrowing to improve the evenness of burn may result in a sufficiently good snail kill.

harrowing also results in turning rocks and disturbing the topsoil, increasing the number of conical snails killed after a hot burn. The first rain will kick-start conical snails, bringing them out from the protection of their summer resting places. Delaying burning until after this point may improve control of conical snails. However, if green material is present, it needs to be desiccated before burning to ensure a really hot burn is achieved.

Burning should occur before early baiting.

Early baiting

Early baiting in March-April is required to ki II snai Is before they become mature and breed. SARDI's research indicates that early baiting should not be limited to fence lines as broad acre baiting is beneficial where round snail popUlations exceed 201m' .

Early baiting last year reduced snail populations between 67-97 per cent on some farms on the Yorke Peninsula and in the Upper South East of South Australia.

The following guidelines may help improve early baiting success.

  • Bait degrades in UV light - you cannot SOUTHERN GRAINS REGION put bait out for long periods and wait for the rain!
  • Delay baiting until a large proportion of snails are active, as snails find bait only when moving.
  • For high levels of mortality the ground needs to stay moist for five to seven days after baiting.
  • Snails mature rapidly in autumn after the opening rain. They are immature in summer and egg laying does not occur.

Mature white snails can move over 15 metres in a week and, as activity starts after a rainfall event, baiting should occur as soon as possible after the rain. Baiting rates must be based on snail density. Therefore, snail counts should be taken before baiting and seven days after baiting to assess baiting success.

Program 3 Contact: Ms Megan Leyson 08 8303 9670 e-mailleyson.megan@saugov.sa.gov.au