Cover crop termination techniques affect ground predation within an organic vegetable rotation system: A test with artificial caterpillars

We studied the impact that two agro-ecological service crops or ASC, (vetch and barley), and two different ASC termination techniques (using a roller crimper or green manure) had on predation pressure in an organic vegetable system. We compared these two ASC termination techniques with a biodegradable plastic mulch, commonly used to control weeds in vegetable organic systems, over two consecutive growing seasons (2014–2015). Predation pressure was evaluated by means of artificial caterpillars made of green plasticine. Attack marks left on them were assigned to predators including chewing insects, birds and mammals. The frequencies of attack were significantly correlated with the activity density of carabids. In both experiments, carabid activity density was higher in ASC terminations than in the biodegradable plastic mulch control. Predation rate was significantly higher in the field with vetch flattened by roller crimper, while no significant difference was detected between termination techniques or in comparison with the control when barley was used as an ASC. The rate of ASC decomposition was higher in vetch than in barley and this could be the reason for the higher activity density of springtails in vetch. Carabid activity density was also positively correlated with springtail abundance. In conclusion, our field experiments showed that artificial caterpillars could represent a good standardized method to assess predation pressure in different habitats.