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Growing strawberries with environmentally sustainable strategies

Published: 16 May 2019

Growing strawberries relies heavily on pesticides. Without pesticides, the flowers are damaged by insects, and yields will be low. In a new doctoral thesis, Daniela Weber has investigated alternative environmentally sustainable strategies for strawberry cultivation.

Today, insect pests are responsible for an average of 16-18% loss of agricultural yields worldwide. Global food security is largely dependent on the use of synthetic pesticides for pest control. However, this is causing a widespread loss of insect diversity, putting insect ecosystem services such as pollination and biological control in danger.

– In the future, we need to shift our pesticide-dependency towards other approaches such as integrated pest management, also called IPM. IPM is a broad-based approach that integrates different approaches, both chemical and biological, to control pests in a more economic and environmentally sustainable way, says Daniela Weber.

Strawberry cultivation - highly dependent on pesticides

Strawberry is a highly pesticide-dependent crop. Ideally, to protect pollinators, synthetic pesticides should be avoided, but reduced pesticide use often results in flowers getting damaged by insects. This leads to lower yields.

Daniela’s research shows that when flowers are damaged by the strawberry leaf beetle, this causes lower yield and also, indirectly, lower pollination. Pest-damaged flowers yielded smaller fruits, even when pollinated by hand, and were avoided by pollinators.

Feeding damage caused by larvae and adult beetles of the strawberry leaf beetle on woodland strawberry A) leaves and B) flowers. Photos: Daniela Weber.
Seasonal life cycle of the strawberry leaf beetle feeding on a woodland strawberry. Egg laying takes place in spring and is followed by larval development in summer. The beetle larvae pupate in the soil and the new generation of adult beetles overwinter in the soil after a short feeding period in autumn. Illustration: Daniela Weber.

Restoring pest resistance from wild strawberries

Daniela also investigated crop wild relatives like woodland strawberries, that are predicted to have a high heritable variation in resistance towards strawberry leaf beetles. These wild strawberries could prove useful in crop improvement.

– We found that the beetles avoid placing eggs on resistant plant genotypes. Therefore, wild strawberries from Sweden are a promising resource for restoring pest resistance in cultivated strawberries, says Daniela.

Be mindful of natural enemies when modifying plant resistance

On the other hand, modifying plant resistance could also affect the pests’ natural enemies. The research in the thesis shows that the performance of the natural enemies was strongly affected by the foliar chemistry of the leaves. It seems like plant eating insects taste different to natural enemies when the plant resistance was modified. The most important factor for natural enemies was the level of carbohydrates in the leaves.

– Taken together, this work shows that we need a very good understanding of the interactions between crop plants, pests, and mutualists such as pollinators and natural enemies in order to design optimal IPM strategies. We need to routinely include natural enemies when evaluating resistance in crop improvement programs, concludes Daniela.

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