The rhododendron gall midge (or tip midge), Clinodiplosis rhododendri (Felt), is a native pest of Rhododendroncatawbiense Michaux (R.) maximum and their many hybrids during the May to October growing season. The larval feeding damage from this fly can cause discoloration and distorted foliage. This damage can appear as in-rolled, twisted leaves that have turned a yellow color. This can be seen on young leaves that have separated from the bud scale. Leaves attacked in the bud stage may die if the injury is severe. Care must be taken to distinguish this pest damage from similarly manifested damage caused by leafhopper injury, chemical injury, leaf-roller activity and aphid feeding.
This insect over-winters in the soil as a prepupa, with complete pupal development taking place in the spring. The adults are very small (less than 1/16") and may be difficult to detect. Eggs are laid on the undersurfaces or rolled edges of the leaves as soon as they are free from the bud but before the leaves have fully separated from each other. Within three days the eggs hatch, and the larvae, which are small white maggots, start to eat leaf tissue within the moist, protected area of the inner surface of the leaf roll. The larvae mature in about seven days, drop to the ground and pupate in the top one inch of soil inside a flimsy, silken cocoon.
Work done in Connecticut showed that most midge populations will complete three generations, but depending on growing conditions, this could reach four to five generations per year.
Early season damage, if present, should be visible in early June. It appears that infestation of the first growth flush is considerably less (20% infestation) than the second and third growth flushes (95% infestation combined). This is an important fact to take into consideration in order to protect the crop. Early detection and treatment will greatly reduce the pest population and thus, the damage in later growth periods.
At this time there is still little information available on non-chemical alternatives for control. A cultural practice that may have some value as a control strategy is to disturb the soil around the plants so that the pupae are exposed to harsher environmental conditions. This may not be practical due to the time involved. Other cultural practices are to maintain healthy plants so that they can survive any damage caused by an infestation or to prune off and destroy newly infested foliage that contain larvae.
Prepared by:Tim Abbey Extension Educator, Nursery. Reviewed by UConn Home and Garden Education Center 2004
The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others that also may be available. All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law. Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations. The user of this information assumes all risks for personal injury or property damage. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, the University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.