Hemerocallis gall midge

(Contarinia quinquenotata)

Hemerocallis gall midge is one of the few pests that attack hemerocallis (daylilies). It causes large, swollen flower buds that fail to open – meaning no flowers.

1. Affected flower buds are swollen – shorter and fatter than normal
2. Affected flower buds fail to open – either rotting or drying up
3. Small, almost clear maggots inside flower buds

The adult hemerocallis gall midge is a small fly – or midge. The female flies lay their eggs in the developing flowers buds of daylilies in May and June. These hatch into larvae, which feed inside the buds, causing abnormal flower development. Hundreds can be found in each flower bud.

The larvae look like almost transparent, small maggots, up to 3mm (less than 1/8in) long. As they feed, a watery liquid develops inside the bud, often making it difficult to see the larvae.

Once fully fed, the larvae drop into the soil and overwinter inside silk cocoons. The adult midges emerge in May-June and the lifecycle repeats again. There is just one generation per year.

The first hemerocallis gall midges were recorded in the UK in 1989, and have since spread to many parts of the UK.

• Daylilies (Hemerocallis)

The larvae feed inside the flower buds causing them to develop abnormally. They become swollen, shorter and fatter rather than the normal long and slender shape.

The affected flower buds either rot on the plant or dry up without opening – resulting in no flowers. Damage is done by early to mid-July.

It is important to check hemerocallis plants regularly, looking for the abnormal flower buds, and deal with them as soon as you see any symptoms developing.

Carefully pick off and destroy affected flower buds.

A systemic insecticide applied during May and June can reduce infestations.

Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to the danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.

There is very little you can do to protect your daylilies or prevent hemerocallis gall midge attacking them.

Late-flowering varieties may escape attack.

• Insecticides
• Secateurs

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