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Beware hungry molluscs

Growers are being warned that high slug populations could mean that an application of pellets is entirely consumed within just a few days of treatment.

Growers are being warned that high slug populations could mean that an application of pellets is entirely consumed within just a few days of treatment.

According to Agrovista’s technical manager Mark Hemmant, trapping results are revealing up to 100 slugs per metre square. “So if just 40 pellets are applied and they are all taken, another 60 slugs will escape control,” he explains.

“In high risk situations, employ the full rate, maximise baiting points, and regardless of pellet quality, go back and check the site soon after application. It’s also important to be prepared to treat again,” he says.

Highlighting the issue that intense slug pressure presents for metaldehyde stewardship, Mark notes that for many, a single application will absorb the maximum 210g limit. “And for those coming out of potatoes, there will be no choice other than to seek an alternative given the metaldehyde restrictions are based on the calendar year and not per crop.

“Elsewhere, the dominant feature of watercourses surrounding fields will mean an alternative is immediately favoured.”

He says that ferric phosphate has proven itself as a valuable new component of the slug control strategy and will feature strongly in programmes this year. “Word of mouth has spread and it is clearly acknowledged that it works. In fact, we are finding that it lasts longer in the field than some alternatives. The active won’t leach out of the pellet, so as long as the pellet is still there, it is still effective – even if the natural dye colour has started to fade.”  

He adds that Derrex, containing ferric phosphate, is a new formulation that Agrovista are marketing for the first time this season. “As a small ‘mini’ pellet it offers lots of baiting points at the full 7kg/ha rate, and that’s vital this season. Meanwhile, the quality pasta based content provides persistence and it spreads very well.”

With the option to apply up to 28kg/ha per crop (not calendar year) there is also scope for repeat applications, and with a strong environmental profile Derrex offers peace of mind, both in relation to water and wildlife. “We need a number of options in the slug control armoury and in employing alternatives to metaldehyde in the way of ferric phosphate, and indeed seed treatments, growers are actually playing a role in preserving metaldehyde’s future.

Mark Hemmant’s only word of caution in relation to Derrex and other ferric phosphate formulations is that unlike metaldehyde, dead slugs are unlikely to be found on the soil surface. “The mode of action means that while the pest stops feeding on the crop immediately, it will crawl away and die underground. So it’s important to judge control by assessing the crop instead,” he advocates.