Before we discuss control of damage from midge in the rose garden it is a good idea to fully understand this insect’s life cycle. Any system you may choose to limit midge impact will be linked to this reproductive rhythm. The insect completes one life cycle every 12-16 days. The warmer the season the more rapid this cycle is finished. In the spring the adult female emerges from the ground and mates laying eggs in the delicate new growth shoots of the rose bush under attack. Within 2 days the eggs hatch and the emerging larva (maggot) begins feeding on the internal structure of these leafy tips. This goes on for 5 to 7 days until the mature larvae drops to the soil and pupates by constructing a white silk cocoon beneath the ground surface. It is the damage to the new rose growth that results in the complete lose or distortion of the rose bud. Control of this midge damage requires interference with this insect’s life cycle. This can be done at the soil level or on the foliage itself. Applications of substances that linger in the soil for long periods are the most effective method of control because this kills the larvae as they begin to pupate into adult insects, remain active for relative long periods, and are ready to attack the pupating larvae whenever they may fall to the ground. Sprays that are applied to the bush kill on contact with the insect or larva and require more precise application timing. The most often recommended product in our geographic area is a granular formulation containing the chemicals imidaclorid (Merit) and cyfluthrin and sold as a Bayer Advanced “Complete Insect Killer”. This is also available in a concentrated liquid packaged in a hose-end sprayer applicator. One ground application is effective for up to three months and is best applied in early spring when the young foliage is emerging and again in mid-summer or early fall. There are other products but this formulation seems to be the most convenient and effective.
So far researchers have not been able to come up with a good biological control for rose midge. The only scientific study published in the horticultural literature on in subject of rose midge control appeared in 2006 authored by Dr. Janice Elmhirst, director of the Elmhirst Diagnostics & Research Corp. and was performed in selected test gardens located in British Columbia, Canada. This study compared two biological agents, two live predator insects, a chemical control, and an untreated control plot. The two biologicals tested are commercially available, one being AVID (with the active ingredient abamectin derived from the soil microorganism Streptomyces avermitilis and the other DOKTOR DOOM®, a ready to use permethrin formulation. The predators were a nematode (Steinernema feltiae) and a predatory mite in the form of an unidentified Hypoaspis species. The chemical control was Matador (lambdacyhalothrin), which is similar to the active ingredient in the Bayer chemical products mentioned earlier. The results of this study were interesting in that the predatory insect approach actually had a higher level of midge damage than the untreated controls. The best result came from the Doktor Doom product with less than 2% damaged rose growth. The next best was the chemical control with approximately 4% damaged tips. The Avid did better than the control but not by a significant amount.
Widely available permetherin products are most often sold as an aerosol spray. There are a few besides the Doktor Doom including Bonide’s one called “Spider and Ground Bee Killer.” All these products are expensive primarily because of the packaging and treat a very limited number of rose bushes. There are veterinary permetherin products used to against flees that are much cheaper but Dr. Elmhirst, when asked about these products, cautioned that they may contain other substances which could be toxic to plant material and should be used only with extreme caution. Also the permetherin substances are highly toxic to fish and aquatic life and are only EPA approved for limited use in horticultural production even if they are considered an organic substance.
So as of now the best approach still seems to be the application of the Bayer Complete Insect Control products. Please remember always follow the label instructions when applying any insect control, no matter how aggressively it may be advertised as “green or environmentally friendly.”
Currently there is only one control that is likely to rid the garden of rose midge. This is a product containing cyfluthrin. The Penn State University recommends the formulations of cyfluthrin and imidacloprid, deltamethrin, lambda-cyhalothrin (Battle GC, Demand CS, Scimitar CS, Scimitar GC, and Scimitar WP only), and pyrethrins and piperonyl butoxide. The most readily available formulation is from Bayer. They have two products that can be useful in the rose garden. The first is Bayer Advanced Power Force Multi-insect Killer (also available in packaging labeled Complete Insect Killer). This is a granular blend that should be applied in the spring when the bushes begin to leaf. The second product from Bayer is Bayer Advanced Garden Rose & Flower Insect Killer. This is applied as a spray. If you have an infestation of rose midge, multiple applications will be required every 10 days. This is necessary because of the insect’s rapid and varied reproduction pattern. Don’t forget to spray the ground around the bushes as well as the foliage.
Monthly applications of the granules are also effective if you are not spraying for other diseases.
The only reported effective non-chemical control for rose midge would be daily removal of affected new growth tips and destroying the debris. This prevents of larva from dropping to the ground and pupating into new insects. Do not compost the remove plant material for this will allow the life cycle to continue in and around your garden. This requires diligent daily inspection of the new growth to detect the infestation and remove the plant part before the larva (sometimes referred to as maggots) fall to the ground.
There is some anecdotal reports that removal of any mulch and loose soil around the plants in late fall will remove the embedded larva which burrows about 1-2" below the surface. Again this material must be removed from the garden or anywhere within 150 feet to prevent return of the insect.