Unmown ground cover mitigates the negative effects of insecticide on ground spiders in apple orchards

In agroecosystems, natural enemies are important for sustainable agricultural production. Several studies have shown that spiders prey on pests and contribute to pest density control in apple orchards, making it important to develop orchard management methods that reduce the negative effects of chemical disturbances on such spiders. Here, we showed that unmown ground cover mitigated the negative effects of insecticide on ground spiders by shielding them from sprayed insecticide droplets. We compared the proportions of the ground surface wetted by spray droplets among four ground cover conditions. Also, we set up four treatments (with and without ground cover mowing and insecticide spraying) and compared the numbers of spiders trapped by pitfall traps. As a result, with unmown ground cover, the proportion of ground surface wetted by the spray droplets was small. Also, the number of spiders in the traps under unmown ground cover was not decreased by insecticide spraying, whereas spraying significantly decreased the number under mown ground cover. These results suggest that unmown ground cover helps conserve ground spiders by decreasing the number of spray droplets reaching the ground surface.