Herbs could keep slugs off the scent
Herbs could keep slugs off the scent
HERB extracts could help farmers combat slugs with less impact on non-target organisms in future.
Currently, the two main approved treatments to control slugs are applications of pellets containing either metaldehyde (such as Escar-Go, Metarex, Optimol, Mini Pellets) or methiocarb (Decoy, Draza, Exit).
Neither compound was originally developed as a molluscicide and concern about their impact on wildlife surrounds their use. To get away from chemical control methods Dr Andrew Martin and colleagues at IACR Rothamsted are trying to develop the use of extracts from aromatic herbs to reduce slug feeding. An extract from tarragon seems particularly effective.
Key to the work is a reliable test to measure how much a slug eats. This is more tricky than it sounds. For example, groups of slugs may follow slime trails, leading them to eat food that would not otherwise be preferred. There is also the problem of accurately weighing how much a slug has consumed. Test foods can lose moisture during feeding trials, or become covered in mucus, so their initial and final weights are difficult to compare.
Dr Martins research has overcome these problems by making a uniform bait – wheatflour pellets. These pellets can be dried and weighed before and after the trial without affecting their quality. Various concentrations of different additives can then be included in the mixture.
The team has tested the effects of extracts from several plant species, together with sucrose, which is known to stimulate slug feeding.
Those from certain herbs markedly reduced slug feeding activity. Plants with the greatest antifeedant effects were rosemary, peppermint and tarragon. Pellets laced with extracts from these herbs reduced slug feeding by 60, 68 and 80% respectively.
Experiments are now under way to test seed treatment formulations of those herb extracts. "On a lab scale, some protection can be conferred for a while", Dr Martin reveals. In the future, it may even be possible to genetically modify crops to produce the antifeedant chemicals. Mint-flavoured lettuce may not be popular with consumers, but seed crops such as oilseed rape could benefit from such breeding without affecting the end productn
Herb extracts put slugs off feeding in trials. Modifying crop plants to produce the same chemicals could confer the same protection in future.
HERBBAIT
• Extracts reduce slug feeding by up to 80%.
• Rosemary, peppermint and tarragon best.
• Seed treatments confer some protection.
• Breeding anti-feedant chemicals into crops may help in future.