Hemerocallis gall midge

Hemerocallis gall midge can affect the ability of daylilies to produce healthy flowers. New to Britain in 1989, the midge is now widespread in England and Wales and is established in parts of Scotland.

Galled buds on the centre and right flower stems, the left stem has normal buds.

Quick facts

Common name Hemerocallis gall midge, daylily gall midge
Latin name Contarinia quinquenotata
Plants affected Daylilies, Hemerocallis species and cultivars
Main symptoms Abnormally swollen flower buds that fail to open
Caused by Larvae of a small fly
Timing Late May-early July

What is hemerocallis gall midge?

Hemerocallis gall midge is a tiny fly that lays eggs on the developing flowers buds of day lilies. The feeding activities of the larvae inside the buds cause abnormal bud development and these buds fail to open. 

Survey

Seen the hemerocallis gall midge or its effects? We would like to know.

As part of RHS research we would like to know where the hemerocallis gall midge has been seen.

Please submit your records via our hemerocallis gall midge survey (expected time to complete survey = two minutes).

Submissions to our pest and disease surveys are stored permanently in an anonymised form in order to monitor the spread of the pest or disease. We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.

Thank you to everyone who has submitted records so far – read a blog about the surveys 

 

Symptoms

If the foliage of daylilies appears normal but the flowers abnormal in the ways described below, hemerocallis gall midge is almost certainly to blame;

  • Affected flower buds are shorter and much fatter than healthy daylily flower buds
  • Such buds fail to open and either dry up or rot
  • Numerous almost transparent maggots, up to 3mm long, may be found inside the buds, crawling around in a watery liquid
The gall midge affects flower bud from late May to early July, later flowering varieties are less likely to be affected. 

Control

Hemerocallis gall midge affects the flowers but not general health of host plants.

Non-pesticide control

Pick off and destroy galled buds as soon as they are seen. Encourage other gardeners who grow daylilies in nearby gardens to do the same. Damage by this insect comes to an end by mid-July.

Some hemerocallis species and cultivars (pdf document) have all or most of their flowering period after the gall midge’s egg-laying period (May-July) is over and so most of their flower production is unaffected.

Pesticide control

  • None of the pesticides currently available to home gardeners has a label recommendation for use against hemerocallis gall midge. However, RHS research has shown that systemic neonicotinoid insecticides applied according to manufacturer's instructions during June can reduce can reduce, but not eliminate, the amount of damage. One systemic product based on acetamiprid (e.g Bug clear ultra) is available
  • Note: these sprays are not suitable for use on plants where it is intended to use the flowers for culinary purposes
Follow label instructions when using pesticides.
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

 

Download

Pesticides for gardeners (pdf document)

Biology

Hemerocallis gall midge has one generation a year. Adult midges emerge in May-June and lay eggs on the developing flower buds of daylilies.

The larvae feed inside the buds causing them to develop in an abnormally. Instead of being long and slender, infested flower buds are shortened and have an enlarged conical shape. The larvae are up to 3mm long and almost transparent, which can make them difficult to see in the watery liquid that accumulates between the petals in the base of the bud. Nearly 400 larvae have been found in a single flower bud; this is likely to be the progeny of more than one female midge.

When fully fed, the larvae go into the soil where they overwinter inside silk cocoons. Galled flower buds either rot or dry up without opening.


Gardeners' calendar

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.