Here's some information that may be useful to you. It's a long post, because I'm going to share just about everything I know.
Combatting Rose Midge Without Pesticides:
• Soil barriers: You can cover the ground beneath each rose with soil barriers such as cardboard, newspaper, or plastic sheets from tarps, trash bags, or painter's plastic. Do this during the growing season as long as needed to interrupt the life cycle – it could be needed for weeks or months (but leave a small opening near the base of each plant where you can insert a garden hose to keep the bush watered). This barrier prevents the midge larvae from burrowing into the soil to pupate, after falling off the rose bush onto the ground. It also prevents any midge that are already pupating in the soil from emerging from their cocoons and flying back up into the rose bush. Keep in mind, however, that new midges can still fly into your garden from outside your yard every single day, so you will still see midge damage, but not as much if you didn't use a soil barrier. This can help to prevent the midge population from exploding in your garden so that you can still get some blooms if you're fortunate.
• Repellant sprays: For small gardens you can get a handheld spray bottle, or for large gardens you can get a tank sprayer that is manually pumped or battery operated (I have a 4-gallon battery operated backpack sprayer). You can then get sprayable cedar oil concentrate or garlic extract concentrate (or both) and spray your roses every few days with a diluted formula. This may help to repel the midge the same way these products are used to repel mosquitos. Apply the spray in the very early morning or in the evening at dusk when most pollinators like honeybees and bumblebees are no longer foraging. If you spray them, it will irritate them. They won't attack you for it, but you'll make them unhappy, and potentially unwelcome by their fellow bees when they try to return to their hives.
• Note that the above approaches are focused on killing the larvae, not the adult midge flies. The adult's lifespan is short (a couple of days), and their presence is fleeting, and new midge flies are constantly entering the garden on a daily basis. Presumably you could spray your rose bushes with an insecticidal soap or horticultural oil to smother them when present, but they are hard to see. Also, as soon as the spray dries, new midge flies would arrive in the garden from outside the property so you'd have to be spraying your roses all the time, and killing other insects while doing it (including pollinators and beneficial predators like ladybugs). However, some folks have had success using sticky traps, or by coating bright yellow and red plastic cups with oil and hanging them upside down around their rose bushes atop sticks, plant stakes, or wooden dowel rods. If the midge happen to land on the cups, they get stuck to the oil. Of course, these approaches can also kill other small insects besides midge that come into contact with the sticky substances.
Combatting Rose Midge with Insecticides
• There are two kinds of insecticides: contact and systemic. Some insecticides work only as one or the other, while some insecticides work as both. Contact insecticides kill insects upon physical contact. Systemic insecticides work by being absorbed into a plant's tissue (either through the roots or leaves), where chewing insects are killed by eating and ingesting the plant's tissue.
• Chlorantraniliprole is an insecticide that comes in granular form (e.g., Scotts GrubEx) and in liquid form. It can be applied to the soil beneath the rose bush and watered in with a garden hose. It can kill midge larvae that have fallen to the soil and come into contact with it, especially if the soil is wet or moist. It does not kill earthworms. As a systemic insecticide it can be absorbed through the rose's roots and spread throughout the bush's canes and leaves. When midge larvae eat the plant's tissue, they ingest the insecticide and die. Note that Chlorantraniliprole is not effective as a contact insecticide spray for rose eggs and larva, because they are embedded within the plant's tissue and folds where the spray doesn't reach them directly.
• Imidacloprid (NOT recommended by me) is sold under the brand names of Merit, Premise, Pre-Empt, Maxforce, and others. Gardeners have successfully used it to combat midge, but I do not recommend or use it. It is both a contact insecticide and systemic insecticide, and comes in both liquid and granular form, and is sometimes combined with Cyfluthrin. As a liquid concentrate, it can be used as a soil drench beneath the rose bush. When midge larvae fall to the ground, they may die after coming into contact with the residue, especially when the ground is wet. Also, as the rose bush gradually absorbs Imidacloprid through its roots and systemically spreads it into new growth, midge larvae will die after eating contaminated plant tissue.
However, Imidacloprid is extremely toxic to ALL insects and also earthworms. If you apply it as a soil drench, or spread it on the soil surface as granules to be watered in, you'll see lots of earthworms come to the surface within 24 hours, where they will wriggle around and die (it's awful to see happen). When frogs, toads, lizards, etc., come along and eat those worms and other dead insects, they will also die, because it is highly toxic to them. When birds see the earthworms, they will eat them and ingest the poison. If you use Imidacloprid as a foliar spray above ground, beneficial insects, bees and butterflies will die if they come into direct contact with the spray while foraging, or can be harmed by picking it up on their bodies as dried residue in pollen and bringing it into their hives. Butterflies can also ingest it by drinking nectar from contaminated flowers. I do not use Imidacloprid for these reasons, even though it is less harmful than many traditional insecticides that are even more toxic.
This is not an exhaustive discussion of all approaches to controlling midge, but covers much of what I know from having combatted midge in two different gardens over many years.
