Thursday, August 16, 2018
By David Campana
Ohio certified volunteer naturalist
Many people prize roses above all other flowers. The beauty, intoxicating aroma and infinite varieties of this “flower of love” are unsurpassed. With due diligence, its blossoms will grace our landscapes throughout the growing season.
Sorry to say that truth of the Chinese proverb, “A thorn defends the rose, harming only those who would steal the blossom,” only goes so far.
Invertebrates that attack roses include roseslugs, rose leafhopper, Japanese beetles, spider mites, thrips and cane borers. But over the past 10 years, the rose midge (Dasineura rhodophaga) has risen to the top of the list.
The larvae bury themselves in the crevices at the base of new shoots and buds, and feed upon the epidermal tissues. New growth begins to curl eventually, causing it to wilt, droop and fall off.
Eggs are but 0.3mm long, taking two days to hatch. The larvae are white to pinkish in color, up to 1.8 mm long, and take five to 10 days to mature.
They then fall to the ground, spin a cocoon and emerge in five to seven days as adults.
The adults are yellowish, 1-1.25mm long, with short antennae and long legs.
In Ohio, there are typically three to four generations per growing season.
This imported pest was first noticed in New Jersey in the late 19th century. Until 1950, nightly fuming with tobacco smoke in greenhouses and a half-inch of tobacco under the plants outdoors were the only way to control infestations.
Then organic and synthetic insecticides were developed. Foliar sprays and soil drenches containing “permethrin” followed by foliar applications of “lambda-cyhalothrin” worked best.
Applications have to start very early in the growing season and require numerous applications. In applying drenches or granules, it is necessary to expose the bare soil beneath the plant.
Biological controls involving parasitic nematodes and predatory mites proved ineffective. Ohio State University professor Dr. David Shetlar (The Bug Doc), on whose research this article is based, has more insecticide recommendation for those who choose to use chemicals.
For those who don’t, there are manual means of controlling midges. Putting plastic ground cover under rose plants will intercept the larvae before they can get to the ground and weave their cocoons. Without reaching the soil, they will die.
Another method is daily inspection of plants and removing buds showing midge damage.
Adults typically only fly 50-100 feet so infestations further away are not a threat.
While these beautiful plants may involve a significant amount of attention, they are well worth the effort. As Antoine de Saint-Exupery – I never heard of him either – wrote in “The Little Prince,” It is the time you have wasted for your rose that makes your rose so important.
Enjoy your roses, and if you have issues, check out this factsheet to help you find a solution: http://go.osu.edu/roseissues.