HEMEROCALLIS GALL MIDGE : . . . . . Return to the PESTS page.

HEMEROCALLIS GALL MIDGE - Contarinia quinquenotata is a small fly which has been a pest of daylilies in Europe for several decades and was identified in British Columbia, Canada in the Summer of 2001. It is now reported to have crossed the border into the north-western United States. Damage in BC is evident between April and July depending on location. Maggots develop inside daylily flower buds causing them to become inflated, distorted and unable to open properly. Some buds may dry up. Reports indicate that in some cases clumps may be so badly affected that few buds open normally. Early flowering daylilies are typically the most heavily infested and egg-laying may have ceased by the time later flowering daylilies are forming buds, allowing them to escape much of the damage. Infested buds may contain from one or two up to a hundred or more small white legless larvae up to around 0.12" in length which, when sufficiently mature, fall to the ground where they overwinter. Thus far it appears this insect only has one generation each year. In spring they emerge as adults and fly to daylily buds to lay their eggs. Because they are inside the galled buds, larvae are protected from contact insecticides. Also, since the adults are flying for several weeks each season, it will be difficult to provide sufficiently continuous contact insecticide coverage to prevent egg-laying. There are currently no researched pesticide recommendations available for this pest. Treatment involves removing affected buds as soon as it is obvious that they have been attacked. These buds must then be destroyed so that the maggots within them cannot continue their life cycle. Some gardeners destroy the maggots by burning the infested buds, but other alternatives need to be determined where burning is not possible. Do not compost infested buds unless the larvae have already been killed by some means. (It is likely that collecting infested buds daily into a plastic bag and placing the bags of buds in a deep freezer for at least two days will kill the larvae, but this needs to be verified). Some gardeners use early flowering daylily cultivars particularly favored by the midges as "trap plants" to assist in collection of infested buds. Daylilies purchased in pots or with intact budded scapes are more likely to introduce the pest to a new area than daylilies acquired bare-root and without scapes.

Additional information from the Royal Horticultural Society available here.