by Harlow Young
I read with interest Lydia Bates’ article, “River Edge Rose.” She was asking for help and guidance in ridding the species roses in Columbia Park of an unusually abundant crop of rose galls. I assume from her description that these galls are not root galls, but those created by a tiny insect called Rose (Rosa)
Gall Wasp. The wasps stimulate the growth of these galls and are only about ¼-inch long (2- to 3-mm), so it is unlikely for us to see them in their natural habitat earlier in the spring or summer.
Here’s what I have learned from some research into these galls. There are two species of rose wasp that create these galls: the Mossy Gall Wasp (Diplolepsis rosae) and the Spiny Gall Wasp (Diplolepsis bicolor). These tiny wasps actually overwinter inside the galls, emerging in April through June to start the cycle over each year.
The gall in which the larvae of the D. rosae overwinter is commonly called “Robin’s Pincushion Gall.” The gall has a hard center that contains the wasp larvae and is surrounded by a dense mass of sticky branched filaments. This structure gives the appearance of a ball of moss, and its filaments are often brightly colored. Starting off green, then turning pink, to crimson and finally to reddish-brown, they are most colorful around this time of year. A large gall can be up to 10-cm (almost 4-inches) in diameter. Most that I’ve seen, however, are about 2-inches in diameter.
The newly emerged adult wasps start to look for tender expanding plant tissue on which to lay eggs. The female will lay up to 60 eggs at each location. When the eggs hatch in about a week, the larvae will begin to chew on soft new growth, and at the point of “injury,” the rosebush will begin to form a layer of nutritive cells in that spot. As the larvae continue to feed, the plant continues to form concentric layers of tissue called bedeguar that eventually becomes the gall with its characteristic hard center and fibrous outgrowths. The larvae will inhabit the hard center of the gall and winter over inside it. There has been some research into the stimulation of the plant to manufacture these galls or growths, but I could not find a lot of specifics as to this phenomenon.
There is only one generation of wasps per year. This cycle appears to be a symbiotic relationship between the wasp and the rosebush. Some researchers believe that once a particular wasp species is accustomed to a particular species of rose, it will not seek other rose types or species to feed on. And, the gall wasps tend to only feed on species (wild) roses; our modern rose hybrids are not attractive to the wasps.
Some years, like this year in the Columbia Basin, the occurrence of these galls is greater than others. There could be a number of ecological and weather-related reasons for this. Though these galls may be unsightly, there is no known or significant lasting damage to the plant. In most years, the “bloom” of these rose galls also gives rise to a corresponding increase in parasites that like to eat the wasp larvae or prey on the adults that are responsible for the gall.
There are some who think that the appearance of the galls is unattractive, while others see beauty in them, as part of the natural life cycles of both the rose and these small wasps. There are reported medicinal uses for the galls, which we might question. Among them is a remedy against toothaches, a cure for baldness if the gall is mixed with honey and applied to the scalp and a tonic to induce sleep, if a gall is placed under a pillow.
In conclusion, I find no citation that indicates that these are harmful to the plant, or that they are the result of a plant disease. So, don’t lose sleep over these galls, just rub the gall honey on your bald spot before you don your night cap and put a couple others under your pillow and dream of an abundant bloom of your roses this fall, all the while growing a healthy head of hair.
For more info http://en.wikipedia.org/wiki/Diplolepis_rosae
Harlow Young (threegkids[at]frontier[dot]com), ‘Rose Whisperer’, September 2013. Rose Herald, Jo Angelos (angelosfolk[at]gmail[dot]com) & Norma Boswell, (rosybos[at]owt[dot]com), co-eds. Tri-City (Pasco‐Kennewick‐Richland) Rose Society.
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