Snail control starts in summer
Author: Rebecca Barr | Date: 21 Nov 2014
Monitoring of snails using cameras has shed light onto their movement and feeding behaviours in different weather conditions, which could alter the timing of when growers apply bait.
A GRDC-supported project by the South Australian Research and Development Institute and the Ag Excellence Alliance on Yorke Peninsula has found that relative humidity, rather than temperature alone, appears to be a key driver in snail movements.
SARDI Entomology grains researcher Michael Nash says in summer, snails move down to the ground when humidity is above 90 percent but in early autumn, snails respond to lower humidities, at about 80 percent.
“Contrary to previous schools of thought, we’re seeing that snails are moving, but not necessarily feeding after a summer rain. The current hypothesis is that they may initially be rehydrating,” he said.
This behaviour has been seen in Western Australia. After recent heavy rains near Esperance, where harvest was complete, growers observed conical snails that were active, but not feeding.
Dr Nash says this observation has refined recommendations for when to start baiting.
“It now seems snails may not always feed after summer rain so I would recommend baiting in March after rainfall. However, if you do get a good rain during summer, you can put sample bait out to monitor feeding activity then use that information to decide to apply bait across the paddock or wait until later in March,” he said.
SARDI research has shown that baiting before seeding is more effective when there are few feed alternatives and barer soil. Dr Nash recommends a second baiting at seeding where snails are a major problem, particularly around paddock edges or roadsides where reinvasion is possible.
When starting summer snail control, the first step is deciding whether to use traditional cabling or rolling techniques, or the more recent option of windrow burning.
“Growers need to choose between the options, depending on whether they want to retain stubble through summer. If snails are to be burnt, then growers should think about setting up to lay windrows at harvest. Over summer, snails will seek out the windrows for their moisture and then can be burnt once it’s safe to burn the windrow,” he said.
Once the decision to set up windrows has been made, the next key step is controlling summer weeds.
“Broadleaf weeds such as lincoln weed, dogweed and cutleaf mignonette provide habitats for the snails over a hot summer, providing the moisture required to survive,” Dr Nash said.
“Controlling these weeds will remove this habitat and force snails to remain on stubble or in windrows, where they’ll be affected by either cabling or burning.”
If cabling or rolling over summer, a high temperature is critical to success. Previous GRDC-funded research by SARDI has demonstrated that at 40°C air temperature, the ground temperature is about 55°C. At these temperatures, snails that are knocked to the ground by rolling or cabling will dehydrate before being able to move back off the ground. Care needs to be taken when cabling in high temperatures to avoid fire. Growers may consider threading poly pipe over the chain to reduce the risk.
“We have seen that even when snails are on stubble, at extremely high temperatures there is some mortality. Last summer at a property in Warooka, when the temperature reached 46°C, 10 percent of snails died. This summer the GRDC Stubble Initiative will continue investigating the effect of stubble height on snail mortality,” Dr Nash said.
Michael Nash, 08 8303 9537, firstname.lastname@example.org
GRDC Project Code DAS00134
Region South, North