Research

Hemerocallis gall midge damage, left and centre, healthy bud on right. Image: RHS

Hemerocallis gall midge ( Contarinia quinquenotata)

Introduction

Hemerocallis gall midge prevents the normal development of flower buds and has been causing problems for gardeners in the UK since the late 1980s. The RHS entomologists have investigated the biology and host range of this pest, resulting in a list of Hemerocallis species and cultivars that are less likely to be damaged.

Biology

Observations have been made on the biology of the hemerocallis gall midge, Contarinia quinquenotata . This tiny fly lays its eggs in the developing flower buds of day lilies ( Hemerocallis species and cultivars). Small white maggots develop inside the buds, causing them to be abnormally swollen but failing to open (see picture above: damaged flower buds left and centre, healthy flower bud on right.) An infested bud can contain several hundred larvae, which may be the progeny of more than one midge. When fully fed, the larvae are 2-3mm (about 1/8in) long and they drop down into the soil where they overwinter as pupae.

Cultivars less susceptible to damage

The midge has one generation a year, with damage to the flower buds occurring between mid-May to early July. Cultivars that flower after that period escape damage. 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. These cultivars are listed below.

This is not an exhaustive list of late-flowering cultivars and there are likely to be others that are not grown at Wisley.

Cultivars with AGM after the name have received the RHS Award of Garden Merit

Use the online RHS Plant Finder to find suppliers

List 1: Late flowering day lilies less susceptible to hemerocallis gall midge

Apricot
Fairy Tale
La Peche
Ruffled Apricot
White Coral
Apricot/purple
Prairie Charmer

Cream
Joan Senior
Loving Memories
Luminous Jewell

Orange
Azur
Bibury
Blushing Belle
Burning Daylight AGM
Cinnamon Glow
Golden Peace
Golden Scroll
Heaven’s Trophy
H. fulva
H. fulva ‘Flore Pleno’
H. lilioasphodelus AGM
H. multiflora
Jane Graham
Michele Coe
Tetrina’s Daughter AGM
Torpoint
Washington Duke Memorial
Welcome Mat
Pink
Bowl of Roses
Magic Dawn
Neyron Rose AGM
Pink Damask AGM
Pink Prelude
Stoke Poges AGM

Purple
Barbary Corsair
Chicago Sugar Plum
Daring Reflection
Ed Murray
Little Grapette
Little Wine Cup
Mighty Mogul
Pardon Me
Peaks of Otter

Purple/red
Viva Shanti

Red
Amersham
Apple Tart
Chief Sarcoxie AGM
Cynthia Mary
Fiery Messenger
Helios
Missenden
Oriental Ruby
Red Precious AGM
Scarlet Flame
Scarlet Oak
Stafford

Red/yellow
Christmas Island
Yellow
Banbury Canary
Burford
Butterscotch Charm
Cartwheels AGM
Chartreuse Magic
Colour Me Mellow
Corky AGM
Frans Hals
George Cunningham
Gold Crest
Golden Gate
Green Flutter AGM
His Pastures Green
Jake Russell
Janet
Lady Fermor Hesketh
Lemon Bells AGM
Marion AGM
Marion Vaughn
Moroccan Summer
Nob Hill
Nova AGM
Optic Elegance
Stella de Oro
Veiled Organdy
Whichford AGM
Wind Song

Yellow/purple
Rumble Seat Romance

Distribution

The gall midge occurs commonly in Europe but was not found in Britain until 1989, when samples of galled flower buds were brought from a private garden at Weybridge, Surrey, to the RHS Members’ Advisory Service at Wisley Garden. Since then the spread of this pest has been tracked through enquiries made to the RHS advisory service and other sources. It is now widely distributed in England, particularly in southeast England and East Anglia.

Map of Hemerocallis gall midge distribution

Click here to submit a record of Hemerocallis gall midge

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 a 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 of this depends on how thoroughly the galled bud-picking is done and whether nearby gardens also have infested plants.

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Hemerocallis gall midge