## 4 Discussion
Molybdenum is often used in form of inorganic salts in paints and hydraulic fluids to prevent corrosion, however, it can cause hypocuprosis in animals fed on plants high in molybdenum [32]. In snails, molybdenum can adversely impact metabolism of calcium and other functions leading to inhibition of growth and feeding, however it cannot affect snail's mortality [32]. We found comparable higher concentrations of cobalt in the four most effective wood ashes. To the best of our knowledge, there are no reports on the effect of cobalt on arionid slug's behavior or mortality. Cobalt is a relatively rare element in nature. Agricultural chemicals such as fertilizers can be enriched with cobalt to amend soils that are cobalt-deficient. Cobalt ions affect natural proteins in different ways, however, their function has rarely been studied. It is known that higher concentrations are toxic in humans, terrestrial and aquatic animals and plants [33]. Further studies are needed to test physical properties of the most effective wood ashes, and mechanisms of action of the most promising wood ashes. In the second experiment (B), wood ash was used as a barrier for the slugs. The slugs produced an excessive amount of slime in all treatments. The efficacy of beech wood ash was 70% after 48 h (Figure 2). The efficiency of the wood ash was found to be similar to plant powder [17] and hydrated lime [25]. As expected, these compounds cause slugs dehydration and blockage of the breathing structures. Slugs tend to dehydrate in conditions of stronger evaporation across their body, but also through mucus secretion [28]. Slugs' inability to deposit mucus limits their performance and increased secretion could impact their feeding behavior. Further research is needed to confirm this statement. In semi-field trials (experiment C), we were aiming to investigate the impact of different techniques of wood ash (as a barrier or slug dusting) on the intensity of slug attack and slug damage potential (Figures 3 and 4). Oak wood ash was used in this experiment as the most promising material. We achieved the best results in treatments with a combination of both techniques (only 10% of damaged plants by slugs were observed). In the control treatment, more than 50% of plants were damaged by slugs. Previous studies have shown that slugs avoid a dry surface such as continuous lines of sawdust or hydrated lime that are used in a physical barrier [25]. A disadvantage of the physical barriers is low efficiency when they become which is almost immediately when applied to wet soil [2]. [PERSON] [2] suggested a solution for this problem, namely, to place a waterproof collar around the plants and to put the barriers on top of it. The disadvantage of this method is impracticability, increased costs for the waterproof material, and frequent replacement of the material. In crop farming, the practice of incorporating wood ash in the soil has been used, in which context it serves for liming and as an N-free fertiliser rich in major elements, notably p, Ca, Mg, and K. Wood ash changes the soil texture, impacting on the soil aeration, water retention, and salinity [34]. Due to its liming effect and increase in soil organic matter mineralization, wood ash stimulates the soil microflora and microfauna activity and modifies their species composition [35]. Wood ash causes significant changes to the mineral compositions and an increase in pH units of soil in the first five years after application only if incorporated in the soil in high doses [36]. Application of wood ash in slug control programs that is presented in our study would have minor effect on the soil properties. We are proposing wood ash as a physical barrier with lethal properties for slugs. If wood ash would be deposited on a waterproof material as proposed, and frequently replaced, it might come into contact with surrounding soil only superficially. This led us to a hypothesis of its insignificant effects on soil properties.