Allelopathic effects of juglone and walnut leaf extracts on growth, fruit yield and plant tissue composition in strawberry cvs. 'Camarosa' and 'Sweet Charlie'

We conducted an experiment in a heated greenhouse to investigate the effects of juglone (5-hydroxy-1,4-naphthoquinone) and walnut (Juglans regia L.) leaf extracts on yield, growth, chemical and plant nutrient element composition of short-day strawberry cultivars 'Camarosa' and 'Sweet Charlie'. Strawberry plants were treated with 1 mM juglone or walnut leaf extracts (undiluted, or diluted 1:2, 1:4, 1:8). Vegetative and generative plant growth was inhibited strongly by treatment with both juglone and undiluted walnut leaf extracts. Fruit yield per plant, numbers of fruit per plant, average fruit weight, crowns per plant, numbers of leaves, leaf area, fresh root weight, total soluble solids, vitamin C, and acidity were all lower for juglone-treated plants compared to controls. All nutrient elements analysed in leaves were generally lower than in controls for all treatments except 1:8 diluted walnut extract. Results from this study should address concerns about growth inhibition of strawberry plants under walnut-based intercropping systems.