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A pesticide control for the hemerocallis gall midge?

Lead scientist
Andrew Halstead, RHS
Partners
American Hemerocallis Society (part funding)
Start date
2009
End date
2011
Keywords

Hemerocallis gall midge, Research, Contarinia quinquenotata, daylilies, pest control, pesticides, Hemerocallis

Benefits to gardeners

The project found that systemic pesticides available to the UK home gardener can significantly reduce levels of infestation by hemerocallis gall midge.

The problem

This experiment investigated whether insecticides available to the UK gardener will control hemerocallis gall midge.

Hemerocallis gall midge, Contarinia quinquenotata (F Löw) is a common pest of day lilies in mainland Europe. It was not found in the UK until 1989 when it was detected in Surrey, England (Halstead and Harris, 1990), it is now widespread. It is also established in parts of the USA and Canada.

The tiny adult flies lay eggs on the developing flower buds during May and June. The white maggots feed inside the buds, causing them to become abnormally swollen, they then dry up or rot without opening.

No pesticide available in the UK carries a label recommendation for control of the midge and the only suggested control was to remove and destroy galled buds as they develop. This interrupts the pest lifecycle by preventing the larvae from completing their development and entering the soil to pupate. This however, is time consuming and may be of little benefit if there are infested plants in nearby gardens where the galled buds are not removed.

Approach

Hemerocallis 'Cynthia Mary' were planted in four × four randomised blocks. The plants within these blocks were sprayed as the flower spikes were emerging with the insecticides deltamethrin, thiacloprid or acetamiprid, or with water (control). Deltamethrin (Bayer Sprayday Greenfly Killer Plus) has a contact action whilst thiacloprid (Bayer Provado Ultimate Bug Killer) and acetamiprid (Scotts Bug Clear Ultra) are systemic.. These insecticides are approved for use by amateur gardeners on outdoor ornamental garden plants in the UK, but have no specific recommendation for use on Hemerocallis or against gall midges.

During the flowering period, the plants were inspected at one-week intervals and the numbers of galled and healthy flower buds recorded. In the first year of the trial (2009) the plants established and flowered, but no infestation with the midge was observed. Infested flower buds were therefore collected from RHS Garden Wisley in June 2009 and buried in the mulch amongst the plants in the experimental plots to increase the chances of infestation occurring in the following year. In 2010 some flower buds were infested but the level of infestation was low on all flower treatments and statistical analysis was not possible. Further treatment and improvement in the experimental design in 2011 enabled analysis, and gave significant results.

The results showed that the systemic insecticides thiacloprid and acetamiprid significantly reduce infestations of the midge when compared to the contact action insecticides (deltamethrin) and water (control). Despite reducing infestation levels however, they do not give complete control of the midge.

Further information

American Hemerocallis Society

Download the final report

References

Halstead A J and Harris K M (1990). First record of a gall midge pest of day lily (Hemerocallis fulva L.), British Journal of Entomology and Natural History 3 p1-2

Halstead, A. 2012. Hemerocallis gall midge study. Reports on the AHS-funded study of some insecticides against hemerocallis gall midge. The Daylily Journal Winter 2012: 18-20

Advisory information

Advice on Hemerocallis

Hemerocallis gall midge

Hemerocallis gall midge

Hemerocallis gall midge

There are no pesticides currently on sale in the UK for garden use that carry a label recommendation for use against this pest.

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