THE GIANT CORPSE FLOWER, which takes a decade to bloom and stinks like rotting meat, makes a good morning newscast story. And while I agree that everyone should start their day knowing about Amorphophallus titanum, there are many other notable horticultural stories that get less press. Gypsy moths and emerald ash borers sometimes merit a feature as they destroy our woodlands, but such killers as verticillium wilt, Swede midge, and spotted-wing fruit flies remain unknown to the public. And even I, who strives to be in the know, learned some lessons this week when a landscape contractor sent me photos of dying spiraea.
If you can’t quite picture what exactly a spiraea is, you are forgiven, and to add to the confusion, the word is often also spelled “spirea.” The bridalwreath spiraea, a tall deciduous shrub with abundant but tiny white flowers in late spring, was popular in Victorian times and still grows in older neighborhoods. Most would say, however, that spiraeas in general were bit players and never the stars of a garden. Then, about 20 years ago, many new, smaller types of spiraea featuring colorful foliage or flowers, were developed. Prized for their site adaptability and low maintenance, they were installed by the millions in new housing developments, strip malls and roundabouts. I call them “gas station plants” and in such harsh environs they appear with other tough customers like Stella de Oro daylilies, barberries and arborvitae.
So when the contractor sent photos of spiraeas showing smaller than normal leaves and dead branches, I wasn’t immediately sure of the cause. A little digging revealed several scholarly papers concerning a disease called “spiraea stunt” caused by an organism called a phytoplasma. These bacteria-like creatures are transmitted by insects to plants, where they infest the phloem, causing yellowing foliage, stunted, dense growth and gradual decline. Sometimes called “yellows” diseases because of their foliar impact, the proliferation of compact shoot growth is often termed a “witches’-broom.” Normally a serious and sober lot, these colorful terms for a plant in distress clearly indicate that even plant pathologists have a playful side.
What are the chances that the local spiraeas in distress had this obscure malady? I contacted one of my favorite Cornell scientists, and a plant pathologist with an excellent sense of humor, Margery Daughtrey. Margery is the plant disease expert at the Long Island Horticultural Research Institute and keeps tabs on plant problems not just in New York State but across the country. She’s seeing similarly suffering spiraeas on Long Island and in the Hudson Valley, and has confirmed the presence of the phytoplasma using laboratory testing. The test is expensive—in the range of $100—and, as Margery says, most gardeners don’t want to spend money just to get bad news. Commercial nursery growers, however, will want to know if their plants are infected with stunt phytoplasma before they propagate or sell them. Plants suffering from the malady should be removed from the landscape, since they will not recover and there is no remedy.
To contact David Chinery, horticulture educator for Cornell Cooperative Extension of Rensselaer County, email