Effective control of slug damage through tobacco extract and caffeine solution in combination with alcohol

Abstract

Slug (Lehmannia valentiana) is known as a particularly troublesome pest in greenhouse, and commonly controlled by chemical bait molluscicides containing either metaldehyde or carbamate. These chemicals often caused undesirable side effects such as significant toxicity in non-target organisms or contamination in food and environment. We conducted several laboratory trials with natural products such as caffeine and tobacco extract or their mixtures combined with ethyl alcohol to assess their molluscicidal efficiency on slug. Slug mortality was evaluated after the three chemicals were sprayed in various concentrations on the slugs in pots. Ethyl alcohol of 10% provided above 90% mortality rate, whereas 3-7% resulted in below 30% mortality rate. Ethyl alcohol (5-7%) mixed with 0.5% caffeine or tobacco extract increased the slug mortality from 50% to 80%. In no-choice feeding test to investigate the behavioral response of the slug to the food, Chinese cabbage leaves were dipped in a mixture of caffeine (0.5%) and alcohol (5 or 7%). The caffeine mixture appeared to act as a repellent compared with the untreated, but tobacco extract/alcohol mixture (0.5/7%) provided a pattern attracting slugs. When two mixtures of caffeine/ethyl alcohol (0.5/5%) and tobacco extract/ethyl alcohol (0.5/7%) were sprayed on marigold seedlings, slug damage decreased by more than 65% compared with the control. Phytotoxic effect such as leaf burn on marigold seedlings was shown by caffeine/alcohol mixture but not by tobacco extract/alcohol mixture. In conclusion, the mixture of 0.5% tobacco extract and 7% ethyl alcohol could be a proper control method for slug in green house without causing any negative impact to environment or plants.