Strip cropping in practice: Higher slug abundance despite a higher number of slug-predating carabid species

Strip cropping is a farming method in which different crops are grown in adjacent strips in the same field rather than in a field with a single crop (monoculture). This approach can increase biodiversity and help control insect pests, but it is not well understood how strip cropping influences pest slugs.

We compared on 20 farms in the Netherlands slugs and their invertebrate predators in strip-cropped and monoculture fields. Strip-cropped fields varied in strip width (3 - 33 meters wide), number of crops (2 – 9 different crops), farming system (organic or conventional), cereal type (winter or spring cereal) and soil type (clay or sand). We identified and counted slugs and their natural predators using traps placed in cereal crops.

Slug numbers were low on most farms, but strip-cropped fields had 3 to 5 times as many slugs as monocultures. Wider strips tended to have more slugs; while farming system, soil type, cereal type, and number of crops did not influence slug numbers.

We observed around 25% more predator species and 50% more predator individuals in strip cropping, compared to monocultures. The effectiveness of strip cropping to increase predator species depended on the type of cereal, soil type, and the number of crop species grown in strip cropping.

Farmers mostly reported similar slug damage in cereals for both monocultures and strip cropping, although some farmers noticed more damage in other crops within strip-cropped fields, especially in fields with a high number of slugs.

What does this mean for farmers?

Strip cropping increases slug populations, but the effect on crop damage was perceived to be limited by farmers. To reduce risks caused by strip cropping in slug-prone areas, farmers should avoid placing slug-sensitive crops, like cabbage or beans, next to crops that facilitate slugs, such as winter cereals. Despite the higher slug numbers, strip cropping remains a promising practice for enhancing biodiversity while retaining productivity.