It is a most wonderful time of the year in the garden and landscapes. There was too much recent rain, but everything is lush and green for now. Many different hydrangeas are in flower. Pagoda dogwood fruits are starting to show their true blue colors. Calycanthus (sweetshrub) is flowering and the new huge-flowered types, such as ‘Aphrodite’, are a lovely deep red against the blue sky. Fernleaf beech leaves are glistening.
Dawnredwood foliage is soft and the overall tree form is magnificent. Katsuratree leaves (and fruits) are their lovely summer blue-green color. ‘Luscious Lavender’ redbuds are lustrous. Yellow jewelweed flowers are out, along with their orange-blossomed cousins. And the Echinacea (coneflower) trials are just in (as of Tuesday) at Secrest.
On the insect side of the ledger, Japanese beetles have arrived. Leafcutter bees are chewing their hole-punch crescents in numerous plants. Monarch butterflies are aflutter and their offspring caterpillars are out and about on their milkweed hosts. As for plant diseases, earlier infection periods by plant pathogenic fungi are now emerging from a latent period and plants are showing symptoms, from cedar rusts on crabapples and hawthorns to Guignardia leaf blotch on buckeyes. Let us expand on some of these topics.
Coneflower Trials at Secrest. Coneflower (Echinacea) popularity seems ever-increasing, and so are the different cultivars available. In fact there are hundreds. So, how to know which one is best for you? This is where Ohio State University comes in and where OSU’s Secrest Arboretum comes in. Secrest's Jason Veil, Paul Snyder, Matt Shultzman and those on their team are expanding Secrest’s program for plant evaluations.
The replicated coneflower trials, which will include 100 types, are now in, selected shrubs such as hydrangeas and crapemyrtles are coming soon, and Crablandia, our crabapple trials at Secrest are ongoing over the past 35 years. There are additional plant trials of OSU on the main campus in Columbus and in the OSU Extension, Clark County office.
Cedar Rusts. As an ornamental plant pathologist, studying plant diseases for the past 40 years, it seems that I should understand the cedar apple rust suite of diseases that go back and forth between junipers (Eastern red cedar) and plants in the rose family, including crabapple, hawthorn, and serviceberry. Something always puzzling, though, to moi and my compatriot Erik Draper of OSU Extension in Geauga County, is why we do not have more cedar rusts in "Crablandia."
The rust fungi that cause these diseases must cycle between their two widely different hosts so we would say they have a wide host range; junipers and crabapples are not close relatives. Yet these fungi also have a narrow host range; only junipers and plants in the rose family. At any rate, we have always had plenty of crabapples and plenty of junipers at Secrest. We always see the spectacular spore horns of the rust fungus on junipers at Secrest. Our wide range of crabapples in Crablandia include many known to be susceptible to these cedar rust fungi, which are quite evident elsewhere.
But, over the years, there has been very little cedar rust disease on crabapples at Secrest. It's heavy in southern Ohio and Kentucky and north in Wisconsin. Why not Secrest? We are still puzzled but interestingly this year, this spring and early summer at Secrest, we are finally seeing this disease occurring prominently on crabapple types that we have never seen so afflicted at Secrest. What is up?
We certainly do not have a definitive answer, but we suspect that the answer lies in the unusual environmental conditions this spring, namely near constant rain in May and June. This is when infections occur on crabapple, from spores arriving from junipers. Leaf wetness was so extended, and if it was not raining it was muggy. So, we suspect that we just had greater infection pressure. Much like the splitting of sweet cherries that occurred in Northeast Ohio this year due to extended fruit wetness.
Blotches in Buckeye (D)NAtion. As noted with cedar rust diseases, the environment conducive to each disease is one key component for incidence of disease. The other two components of the plant disease triangle are a virulent pathogen, and — plant host susceptibility. So, let us talk of the buckeyes and the beast; the beast being Guignardia leaf blotch disease.
The symptoms of this disease are beginning to show their brick-red to brown lesions on horsechestnut and buckeye foliage now. Again, infections were earlier, during our seemingly endless Ohio monsoons of 2019, and these latent infections are now fulfilling their symptomatic pathological destinies.
As the season progresses, we will see varying amounts of this disease on the different Aesculus types. For example, most horsechestnuts and their cultivars and hybrids are more susceptible than Ohio buckeye, which is more susceptible than yellow buckeye, which is more susceptible than red buckeye, with bottlebrush buckeye being the least susceptible.
This disease eventually becomes a serious aesthetic problem on the more susceptible types. Large, irregular, reddish-brown lesions with surrounding yellowed tissue occur on leaves, often badly disfiguring foliage by mid- to late-summer. Leaf blotches initially with a somewhat water-soaked, grayish appearance are now turning that reddish-brown. Leaves often curl and brown and, by August, the overall plant on highly susceptible types and moist springs often look as if blow-torched. Early leaf drop may also occur.
Those initial infections in spring came from spores of the fungus produced in infected leaves and twigs from the past year. Moist conditions during leaf emergence, such as occurred this year enhance the infections and subsequent cycles of infection occur if moist conditions continue. Black fruiting bodies of the fungus are often evident in lesions by late summer. The disease does not appear to be a serious health problem, as much of the annual growth of Aesculus has occurred by the time foliage is badly damaged.
Recently, during one of the OSU Extension Secrest Arboretum walks, the contrast between two Aesculus types was tell-tale for the importance of DNA. First was one of the Aesculus xcarnea hybrids between common horsechestnut (Aesculus hippocastanum) and red buckeye (Aesculus pavia), namely the soft pink-flowered clone known as ‘Ft. McNair’, selected in Washington. As Michael Dirr and Keith Warren note in “The Tree Book”: These and other A.xcarnea cultivars are “superb park, large area, campus, and golf course tree(s)…that any arboretum should include. Sun and moist, well-drained soils, low or high pH.” The buckeye blotch, though may be bestial.
The second tree for comparison was a cultivar from Minnesota known as ‘Autumn Splendor’. This clone is thought to be a tri-brid of yellow buckeye (Aesculus flava) and red buckeye, with some Ohio buckeye (Aesculus glabra) in the mix . The leaves are smaller than ‘Ft. McNair, the flowers are more yellow-green but spectacular as are all Aesculus types and pertinent to the genetics herein: the susceptibility to Guignardia leaf blotch disease is much less than for ‘Ft. McNair’. Genetics will out. A base pair here, a base pair there…
Von Humboldt Redux. After 250 years, Alexander von Humboldt shall again grace Nature’s stage. On Sept. 13 of this year, one day short of the sestercentennial of his birth, his spirit will grace the Secret Arboretum amphitheater stage, as we shall perform our version of “Humboldt Unbound.” The next day we will host at Secrest a free educational program highlighting the lasting legacy of his transformative views of nature, not to be feared or conquered, but to be embraced. As Charles Darwin said: “If not for Alexander von Humboldt, I would never have sailed on the Beagle.”
We will explore the science of this reality, from climate change realities to the effect of environmental factors on plant growth and development. But we shall also revel in the glorious mixture of all of our senses, the scientific data and artistic sensibilities combined. The philosophy and practice of our ever-broadening efforts to better describe and predict Nature, and also through the power of theater, music, art, and poetry,
Jim Chatfield is a horticultural educator with Ohio State University Extension. If you have questions about caring for your garden, write to email@example.com or call 330-466-0270. Please include your phone number if you write.