By: Baldo Villegas, baldo[at]sactorose[dot]org, Consulting Rosarian & Entomologist
On Friday, August 23, 1996 I visited a rose nursery in Petaluma, Sonoma County, California that was heavily infested with the rose midge, Dasineura rhodophaga (Coquillett) [Diptera: Cecidomyiidae]. Nearly 100% of the new growth in a section of the field-grown roses was affected. The infestation was first detected in early August by the nursery caretaker and confirmed as rose midge by Dr. Bill Chaney, University of California Cooperative Extension Farm Advisor for Monterey County (Salinas) and an American Rose Society Consulting Rosarian.
While at the nursery, I also found scattered damage in the landscape roses and in the potted roses in the sales area of the nursery. Midge damage is very diagnostic. The tiny rose midge larvae feed on the tender new growth and immature buds and what they do not eat, turns black and withers. This type of damage can be confused very easily with foliar burn caused by some pesticides. In most affected areas of the nursery, I saw a complete lack of healthy rose buds and flowers.
The rose midge are mosquito-like in shape and they are 1-2 mm in length (this picture of a closely related species of midge illustrates the relative size of the adult female and adult male in millimeters). They emerge from pupae in the soil early in the spring in synchrony with the production of new plant growth and flower buds. There are several overlapping generations per year and a single generation, or life cycle, can be as short as two weeks. Populations of the midge build up until early fall and the last generation overwinters in the ground in cocoons. Adult midges emerge the following spring.
Females lay their eggs inside the sepals of flower buds or leafy tips. The larvae then hatch from the eggs and damage the buds and rose tips. The full-grown larvae may measure up to 1.8 mm long and are sometimes reddish in color. Pupation usually occurs in the soil but pupae have been observed in the damaged rose tips. They leave the damaged tips after which the buds wither, blacken, and die (this damage is illustrated in the picture shown here.
Rose midge appears to be a native insect to North America. It was first detected in 1886 in New Jersey by a greenhouse rose grower and since that time it has been recognized in many of the eastern and Midwestern states as well as in Oregon, Washington and Canada. It’s appearance in Oregon happened in the last 15 years. The present extent of the infestation in northern California is unknown. It is likely that the rose midge came into California from Oregon on its own. However, the infestation could have also been introduced into California via infested soil or plant materials either sent through the mail or carried from an infested area in North America.
Successful control measures require repeated soil and foliar insecticidal applications. According to the literature repeated applications of Diazinon® to infested soil as well as a foliar spray gave excellent control to field grown roses (Smith and Webb, 1976. The Rose Midge 1976 ARS Rose Annual pp 57-73). In Petaluma, the infested rose nursery has taken preventive control measures against rose midge by spraying the infested soil around the roses with Diazinon and treating the foliage with Mavrik® at a 10-day treatment schedule.
This type of control is definitely needed in a nursery situation in order to control of rose midge as well as prevent spread of rose midge in infested growing trips or in the soil of potted plants. Additionally, any blackened tips should be pruned off in potted roses in the sales area as an added precaution against possible movement of the midge in these roses.
Home gardeners as well as commercial landscapers will need to follow a similar preventive control program consisting of repeated soil treatments and foliar insecticidal sprays. We are lucky to have many insecticides still available to commercial applicators and home gardeners.
In order to get a handle on the distribution of rose midge within California, please check your roses for midge damage, especially if you grow roses in a greenhouse. Please check the 1976 American Rose Society Rose Annual for additional information and pictures of the damage.
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