- Lead scientist
- Andrew Halstead, RHS
- American Hemerocallis Society (part funding)
- Start date
- End date
Hemerocallis gall midge, Research, Contarinia quinquenotata, daylilies, pest control, pesticides, Hemerocallis
- Benefits to gardeners
The project will determine if it is feasible to control hemerocallis gall midge with pesticides available to home gardeners in the UK.
- The problem
The hemerocallis gall midge, Contarinia quinquenotata (F Löw) is a widespread pest of day lilies in Europe. It was first detected in Surrey, England, in 1989 (Halstead and Harris, 1990) and has since become widespread. It has also become 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 and squat. Infested buds usually dry up or rot without opening. Flower buds that develop between late May and the first week in July are liable to be galled.
No garden pesticides currently on sale in the UK carry a label recommendation for use against this pest. As with many host-specific pests of ornamental plants, it is unlikely that a company marketing pesticides would consider hemerocallis gall midge to be a sufficiently important problem to justify the expense of trialing their products against it. Some of the garden pesticides may give protection against this pest, but there is no published evidence to support their use.
The other approach to hemerocallis gall midge control is to remove and destroy galled flower buds as they develop. This prevents the larvae from completing their feeding and going down into the soil where they pupate and overwinter. Removal of infested buds is time-consuming if large numbers of daylilies are being grown. There may be little benefit from this if there are infested plants in nearby gardens that are not having the galled buds removed.
Hemerocallis 'Cynthia Mary' which has its main flowering period during late May-early July has been planted in four, four × four randomised blocks. The plants within these blocks are sprayed when the flower spikes are emerging with either deltamethrin, imidacloprid, acetamiprid, or water (control). Deltamethrin (e.g. Bayer Sprayday Greenfly Killer Plus) is a pyrethroid insecticide with contact action; thiacloprid (Bayer Provado Ultimate Bug Killer) and acetamiprid (Scotts Bug Clear Ultra) are neonicotinoid systemic insecticides that may control the larvae inside the buds. These three insecticides are approved for spraying on outdoor ornamental garden plants in the UK, but have no specific recommendations for use on Hemerocallis or against gall midge pests.
During the flowering period, the plants will be inspected at a minimum of one-week intervals and the numbers of galled and healthy flower buds counted. The trial will be conducted in the experimental plots at Deers Farm in Wisley Village.
In the first year of the trial (2009) the plants establised and flowered. Unfortunately adult gall midges did not manage to find the plants at Deers Farm so it was not possible to tell whether the treatments were having any effects. Infested flower buds were collected from RHS Garden Wisley in June 2009 and these were 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 still not adequate to provide statistically significant results. The treatments will be repeated in 2011 when it is hoped that infestation levels will have built up further.
- Further information
American Hemerocallis Society
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
- Advisory information
Advice on Hemerocallis
Hemerocallis gall midge