Reducing the Damage of the Slug, Agriolimax agrestis Linnaeus using Copper Hydroxide in Greenhouse Conditions

Background and Objectives

Agriolimax agrestis is one of the important pests of greenhouse ornamental plants in Iran and the world, especially in the northern provinces which cause a relatively large amount of damage to them in greenhouses every year. Chemical molluscicide, metaldehyde, is considered one of the most important compounds widely used to control the slug. The compound may cause many concerns for human health and other organisms (aquatic, birds, livestock, etc.) by entering the environment. Therefore, replacing high-risk chemical molluscicides with environmentally friendly and safe compounds can reduce the side effects of pesticides and the occurrence of resistance in this pest to the molluscicides. This research evaluated the effectiveness of Tobalin® as mineral compound 5% SC containing copper hydroxide in reducing the damage of A. agrestis slug.

Materials and Methods

In the laboratory conditions, the effect of Tobalin® (4 ml/L) on slug feeding was investigated by choice and non-choice methods. For the study, the surface of the leaves was measured before the start of the experiment using Image J software (ij153-win-java8), and the eaten surface by slugs was calculated after seven days.
In the repellency test, treatments included: (1) untreated pot and plant, placed on a copper hydroxide-treated substrate (plastic cafeteria tray); (2) sides of pot sprayed with copper hydroxide but plant foliage and substrate not treated; (3) plant foliage and pot treated with copper hydroxide and placed on untreated substrate; (4) untreated plant and pot (water spray only) placed on untreated substrate (untreated control). 60 slugs, each of which was 0.7 to 1 g in mass, were released into the center of the screenhouse, and each pot containing a plant was examined for the presence of slugs. The cumulative number of slugs observed on each plant and pot during 21 d of observation was totaled. The total number of leaves damaged by the slugs was determined at this time. In greenhouse conditions, spraying of concentration of 4 ml/L of Tobalin® with the chemical molluscicide metaldehyde (2.5g/m2) and the mineral molluscicide Ferricol® (5g/m2) as bait and control treatment (water) on ornamental plants Spathiphyllum wallisii was carried out in the greenhouses of Mazandaran and Alborz provinces. The experiment was done in a completely randomized design in 10 square meter plots with four repetitions of 2.5 square meters. Slugs (0.7 to 1 g weight) were released in equal numbers (40 pieces) in each plot on S. wallisii bushes. Then, the damage caused to the plant by feeding slugs was determined on 7, 14, and 21 days after applying the treatments.

Results

According to the results, in choice and non-choice tests, slugs fed on untreated leaves (12.4 and 17.3 square centimeters, respectively) more than Tobalin® treated leaves (6.3 and 7.1 square centimeters, respectively). In the repellency test, the mean number of slugs counted in the plant + pot treatment during 21 days was 0.4 and 0.3, respectively, in Mazandaran and Alborz provinces, which was less than other treatments. Also, the percentage of damaged leaves in the pot plus plant treatment was 20.4% and 22.5% in Mazandaran and Alborz provinces, respectively, compared with control, 73% and 75.25%. In the greenhouse, on the 21st day after the treatment with Tobalin® (4 ml/L), the damage to the plant in Mazandaran and Alborz provinces was 27.2 and 25%, respectively, which were grouped without statistically significant difference with the treatment of bait metaldehyde with the amount of damage, 15.7 and 15% respectively. Considering that from the 7th to the 21st days of the experiment, the amount of damage in Tobalin® treatment is increasing and this compound is not lethal to slugs, repeating the foliar spraying after two to three weeks is necessary for the continuation of its anti-feeding and repelling effect.

Discussion

Mineral compound Tobalin® can be used to deter Agriolimax agrestis. It is worth mentioning that there is no need to use bait when using Tobalin® and this compound can be used as a substitute for chemical pesticides in the integrated management of slugs on ornamental plants in greenhouses.