Cover crops in Victorian apple orchards: Effects on production, natural enemies and pests across a season

Cover crops have the potential to decrease chemical use against pests through promoting an increase in natural enemies providing fortuitous control, particularly in horticultural industries. Suitable plants must be able to grow in appropriate conditions and not compete for nutrients or water. Plants selected for potential beneficial effects on natural enemies without providing resources for hosts were grown as cover crops in three 5–6 year old apple orchards in Victoria, Australia, and compared to two common current practices, volunteer grasses and a commercially available grass mix. The cover crops tested – Queen Anne's lace Ammi majus/fennel Foeniculum vulgare (Apiaceae), chicory Cichorium intybus/yarrow Achillea millefolium (Asteraceae), white mustard Sinapis alba (Brassicaceae), buckwheat Fagopyrum esculentum (Polygonaceae) and fenugreek Trigonella foenum-graecum (Fabaceae) – established at some locations but reseeding was poor. By assessing natural enemies and insect pests across a season with yellow sticky traps, direct searching and an examination of fruit, we found no evidence for an increase in natural enemy activity in the apple trees, but evidence for increased pest and russeting problems as well as a detrimental effect on production in some treatments. These results emphasise the importance of local testing; while cover crops might increase numbers of beneficials under controlled conditions, beneficial effects may not extend to commercial settings particularly in areas with limited (<800 mm) annual rainfall.