Keeping tabs on how crop-wrecking slugs move around could lead to better control. Andrew Blake reports.
Feedback from micro-chipped slugs may help growers control the pests more effectively with fewer inputs. That is the hope of Keith Walters, of Harper Adams University, who is leading a three-year AHDB Potatoes project* which began last October.
Uncontrolled slugs could cost potato, wheat and oilseed rape producers nearly £100 million a year, according to AHDB. But with growing pressure to reduce molluscicide use for environmental reasons, more precisely targeted applications are the way ahead, Prof Walters believes.
The most widely used molluscicide, metaldehyde, is sometimes detected in natural water above the drinking water standard, with peaks following rainfall. Although the levels detected pose no danger to health or the environment, the UK’s environment agencies and Defra are responsible for implementing the Water Framework Directive, the legislation which protects the water environment.
See also: Slug control with zero metaldehyde
Unless action is taken, regulatory restrictions or even withdrawal, may be enforced. After the recent ban on methiocarb, the hope is understanding slug patterns is the key to avoiding these measures.
The new research, by PhD student Emily Forbes backed by modelling help from Birmingham and Leicester universities, is based on inserting 0.5cm-long radio frequency identification (RFID) tags into grey field slugs to allow their movements to be followed.
Prof Walters says: “It’s well known the field distribution of slugs is patchy. We hope to find out whether such patches are stable over time, whether their size is driven by population density, and whether patch location can be predicted from environmental variables such as soil type, moisture, organic matter, pH and bulk density.”
The aim is to evaluate the scope to manage slugs in field crops by targeting control against high density patches and preventing their expansion.
See also: Farming must act now on metaldehyde
“This contrasts with approaches based on trap catches and estimates of population size which have hitherto had limited success.
Although the work is still in its early days, no adverse effects on the slugs themselves have been encountered, he says.
“We’ve undertaken intensive sampling of slug populations in 10 commercial winter wheat and potato fields in Shropshire and this has been coupled with detailed environmental assessments in the same fields.”
“The RFID tagging procedure is novel for this application and effectively allows us to ‘observe’ the natural behaviour of slugs in a solid mass of soil without disturbing it. The concept is effectively the equivalent of ‘seeing through a brick wall’,” says Prof Walters.
Once tagged slugs are released into the field their positions are detected using an antenna which can pick up the individual tags’ unique codes, he explains.
“So, we can follow the movement of an individually identifiable slug for a long period.
“The antenna can ‘look’ 15cm deep into the soil which experiments have shown is sufficient for this work.”
Once found the slugs’ location is noted using a handheld GPS device. “The GPS devices available cannot, for various reasons, be inserted into the animal.
“We’ve field-tested the approach and the slugs are more readily found using this approach than we had initially expected. After an hour or two from release or last detection, we find them very quickly. We’ve even tested a five-day interval between release and assessment, and it took on average about five minutes to find the slugs we used. Early signs are the pests do not move far, but the team is testing the hypothesis this autumn.”
Despite their small size the slugs appear behaviourally unaffected by the presence of the tags after a rather short ‘settling’ period post-insertion, he adds.
Uncontrolled, slugs would hit potato production the hardest (£53 million), followed by wheat (£25m) and oilseed rape (£18m), according to the AHDB’s crop protection scientist (pests), Caroline Nicholls.
“With pressure mounting on the existing, and already limited, control options, the need for new solutions has never been greater,” she says. “This is why AHDB Cereals and Oilseeds and AHDB Potatoes are innovating together to keep the pressure on slugs and off our crops.
“As with much pest research, if control is working well it can become far too easy to overlook the need to understand what makes a pest tick; and it’s only when control is threatened, restricted or lost our lack of knowledge becomes apparent.
“For slugs, the ability to target pellets in parts of fields which need them most would be invaluable. The trouble is we don’t know enough about how slugs behave in the field. Through the use of innovative approaches, the researchers conducting this work have already identified persistent slug patches in commercial crops. By tagging these slugs, their behaviour within the patch should be revealed. This insight into slug patch dynamics should help with developing targeted control by exploiting precision farming technology.
“Through more effective pellet targeting, this project compliments the work of the Metaldehyde Stewardship Group, whom we support, and its effort to promote best practice for metaldehyde slug pellets to minimise risk to water supplies.”