Science Into Practice - Agapanthus gall midge

HNS PO 199: Biology and control of agapanthus gall midge

The agapanthus gall midge was discovered in the UK in 2014. Larvae develop inside flower buds or in closed flower head sheaths, causing the buds to fail to open, sometimes leading to collapse of the entire flower head. In severely infested nurseries it is estimated that it can lead to 70 per cent crop loss.

Very little is known about its biology, life cycle and effective control measures. AHDB funded project HNS PO 199 because it is a potential pest of both container-grown plants and field-grown cut flower plants.

Agapanthus gall midge has a long and consistent period of activity from mid June to early October, indicating multiple overlapping generations. Larvae feed and develop inside flowers and a single flower head can host thousands of larvae. When fully grown, they emerge and drop into the soil to pupate.

There may be some differences in midge infestation between different agapanthus cultivars. Six widely grown cultivars were tested for susceptibility and ‘Northern Star’ had much higher levels of infestation than others. Foliar sprays had no significant impact, likely because products were unable to penetrate into flower buds successfully.

Results of drench treatments were inconclusive because of the natural high mortality rate of the larvae when they pupate in the soil or substrate. Future work is needed to review the optimum growing-media moisture level for successful midge emergence to be able to further test drench treatments.

Further research is needed on both biological and chemical controls. Growers should monitor closely for symptoms as soon as they begin to flower. Remove and destroy any infested flower heads and destroy any badly infested plants.

- For further information, visit horticulture.ahdb.org.uk and search "HNS PO 199".


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