Slug control might be hindered by mud splash
WET weather will not, as is often perceived, help slugs to recover from metaldehyde-based poisons, according to Swiss-based manufacturer Lonza.
But mud splash may interfere with control more than is realised, says a UK specialist.
Fresh research on metaldehyde, which has been used against the pests for nearly 70 years, disproves the hypothesis that it kills them by dehydration, says Lonzas Ignaz Heim. Work at the University of Tubingen in Germany confirms that the poison works by killing slugs mucus-producing cells, even in the wet and at low temperatures.
This particular mechanism could explain why no cases of resistance to metaldehyde have ever been seen, adds Dr Heim.
Control failure is much more likely to be due to spreading too few pellets, he says. "Application rates are often reduced, resulting in inadequate pellet densities below the recommended 40-50/sq m."
Slug specialist David Glen of IACR-Long Ashton agrees there is growing evidence that metaldehyde does not work by desiccation. "Our field trials show you can get good results in really wet weather."
Insufficient baiting points is one reason for poor results, he adds. Products that break down quickly after rain may also prove disappointing. "Another problem may be the sheer numbers of slugs in an autumn like this."
But mud splashing of pellets may be more significant than previously realised, says Prof Glen. "As far as I can see, it would not be specific to any active ingredient, but it is something we hope to investigate through a new MAFF LINK project."
The work could help explain why products effective in wet laboratory conditions are less so in similar conditions in the field, he says. *
metaldehyde for slugs
• Desiccation not involved.
• Rain not impairing effect.
• Too few pellets = poor control.
• Mud splash masking pellets?
Heavy slug pressure demands widespread pelleting this autumn. New evidence suggests metaldehyde is unaffected by wet weather.