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Rose Midge

Insect keeps roses from blooming

By: Sandy Feather ©2011
Penn State Extension


Q: I planted three Knock Out® roses several years ago and was quite happy with their performance at first. Last year, they did not bloom at all. It seemed like they formed flower buds that never opened – they just turned brown and shriveled up. The plants look great – whatever it is doesn’t seem to hurt the plant. Do you have any idea what could have caused this and how I can get them to flower again?

A: Rose buds that turn brown and fail to produce flowers while the plant looks fine  are classic symptoms of attack by an insect called the rose midge (Dasineura rhodophaga). Rose midges can also damage vegetative buds and stems, and cause deformed flowers that do not open properly. This pest overwinters as a pupa in a white silken cocoon in the soil under infested plants. Adults emerge in late spring as soil temperatures warm. You may get to enjoy the first crop of roses if soil temperatures remain cool early on, but once the adults emerge and begin laying eggs, you would be lucky to see even one normal flower.  Many generations develop through the growing season.


Midge Eggs

Female rose midge adults lay their eggs in flowers buds or expanding leaf buds, or even the tender tissue of elongating shoots. Those eggs hatch quickly and the young larvae immediately begin to cut into tender buds and stem tissue to get to the sap that is their primary food source.

Double Knock Out Rose
Double Knock Out® Rose

The injured tissue dies, turning brown at first, then black. It is common to find as many as 10 - 15 rose midge larvae on a single bud. They are very tiny - less than 2 millimeters long - so they often go unnoticed until you miss the flowers or notice dead buds. You can see the creamy white to pale red larvae on close inspection, but they are very small. They mature in about a week. Some drop to the ground to pupate, while others pupate in the injured buds or stem tissue. It only takes about two weeks for them to complete their entire life cycle during warm summer weather. Adults are small, inconspicuous reddish-brown flies. They do not feed at all, and only live for a day or two.

 


Rose Midge Control

Controls targeted at the first generation can drastically reduce or even eliminate the need for treatment later in the season. The only organic control that seems at all effective is to cover the soil under infested plants with plastic or layers of dampened newspaper. The idea is that adults have a difficult time getting out of the soil and die. It seems likely this approach would be more effective with plastic mulch that heats the soil enough to kill the pupal or adult stage of this pest.


Insecticides

Bayer Advanced Power Force Multi-Insect Killer (cyfluthrin), Bayer Advanced Garden Rose & Flower Insect Killer (cyfluthrin and imidacloprid), and pyrethrins and piperonyl butoxide are labeled to control rose midge in Pennsylvania. Start making applications as roses begin to leaf out in the spring. Make two more applications at ten-day intervals to ensure good control. Although many organic gardeners prefer to use pyrethrins without piperonyl butoxide, pyrethrins alone may not provide significant control of rose midges.
  


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