Rose midge

About

A tiny yellow-brown to reddish fly, about 0.05 inch long, first reported damaging roses in New Jersey in 1886 (PNW Handbook, Oregon State). Its tiny whitish maggots feed inside rose buds and shoot tips (Minnesota).

Spotting it

Damage

Buds and shoot tips become bent and misshapen, then turn brown or black and die; damaged buds give deformed flowers or none (PNW Handbook, Illinois). In an Oregon trial, 54% of buds on untreated roses were damaged.

How to find it early

Watch new shoot tips and buds for blackened, shriveled tissue. Pull a damaged bud apart and use a magnifier to look for tiny maggots near its base (Minnesota). In California, take suspect samples to your county agricultural commissioner, and don't confuse them with a helpful midge whose larvae eat aphids (UC IPM).

When

Late spring through fall. Oregon State saw damage peak in late June to early July and again in late August to early September; Illinois says damage often shows in July.

Life cycle

Females lay eggs under the sepals of flower buds or in new shoot tips, and the maggots feed, then drop to the soil to pupate (PNW Handbook, Illinois). It spends winter as a pupa in the top 1 to 2 inches of soil and has 2 to 4 generations a year (Oregon State, UC IPM).

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Start clean and refresh mulch Prevent

   Buy bare-root roses, or discard the soil and rinse the roots of plants that come from infested gardens. Removing old mulch in late fall and putting down fresh mulch may take away the overwintering pupae (Oregon State).

2. Cut out damaged tips By hand

   Prune off and destroy infested buds and shoot tips as soon as you see them (PNW Handbook, Illinois).

3. Fabric under the plants Barrier

   Illinois Extension suggests laying weed barrier fabric under roses to catch larvae as they drop, so they cannot reach the soil to pupate.

4. Pyrethroid sprays, as a last resort Conventional spray

   Mississippi State lists pyrethroids such as bifenthrin, cyfluthrin, cyhalothrin and permethrin for home gardens, sprayed on the soil, mulch and leaf litter under the roses every 14 days from leaf-out. In an Oregon State trial, cyfluthrin sprayed every two weeks all season (12 sprays) held bud damage to about 2%.

   That is a lot of spraying. Pyrethroids are highly toxic to bees, and cyfluthrin and bifenthrin residues can stay toxic for more than a day (PNW 591), so never spray open flowers. Mississippi State also lists an imidacloprid soil drench; it is a neonicotinoid that harms pollinators, so skip it. Read and follow the label, including its pre-harvest interval if you eat any part of the plant.

Plants it goes after

Apothecary rose, Rose (garden and landscape roses)

Pressure by region

Oregon State lists it in the Pacific Northwest, the Northeast, Colorado, Illinois, Ohio and Wisconsin and expects its range to grow. UC IPM says it was found in one California nursery in 1996 and has not been reported there since. All other ratings are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.