Hemerocallis gall midge (Contarinia quinquenotata) prevents the normal development of flower buds of daylilies and has been causing problems for gardeners in the UK since the late 1980s.
Description and life cycle
Hemerocallis gall midge is a tiny fly that lays its eggs in the developing flower buds of daylilies (Hemerocallis species and cultivars). The midge has one generation a year, with damage to the flower buds occurring between late May to early July. Cultivars that flower after that period escape damage.
Small white maggots develop inside the buds, causing them to become abnormally swollen and fail to open. When fully fed, the larvae are 2-3mm long and they drop down into the soil where they overwinter as pupae.
An infested bud can contain several hundred larvae, which may be the progeny of more than one midge.
From observations made on the extensive Hemerocallis collection at RHS Garden Wisley, a list has been compiled of late-flowering cultivars that partly or wholly miss the egg-laying period of the gall midge.
Download the list of Hemerocallis less prone to damage.
Distribution
The gall midge is widely distributed in Europe but was not found in Britain until 1989, when samples of galled flower buds were brought to the RHS Members’ Advisory Service at Wisley Garden from a private garden in Weybridge, Surrey. Since then the spread of this pest in Britain has been tracked primarily through this web survey and enquiries made to the RHS Advisory Service, this web survey and other sources. It is now widely distributed in England, and has become established in Scotland and Wales.
Control
- None of the pesticides available to amateur gardeners carries a label recommendation for use against gall midges.
- The larval stage is concealed within the buds and therefore difficult to reach with pesticide.
- The adult stage is more vulnerable but is active over a period of approximately six weeks during which egg laying can take place.
- Galled buds should be picked off and destroyed before the larvae are able to complete their feeding. This will reduce damage in the following year but the effectiveness depends on how thoroughly the galled bud-picking is done and whether nearby gardens also have infested plants.
Further research
The RHS is investigating the possibility of controlling Hemerocallis gall midge with pesticides that are available to amateur gardeners. Read more