James A. Chatfield
Nancy J. Taylor
Stephen N. Nameth
Chris Carlson
Joseph F. Boggs
Jane C. Martin
Dan Balser
David Madison
This article is drawn from reports in the Buckeye Yard and Garden Line (BYGL) throughout the year, reports from the C. Wayne Ellett Plant and Pest Diagnostic Clinic (PPDC), reports from the Ohio Department of Natural Resources, and reports from the Ohio Department of Agriculture nursery inspectors.
Bulletin 614, Disease Control in the Landscape, is a key resource for the green industry and homeowners, complete with more than 100 color pictures. Included in this bulletin are general principles of plant health management, diagnosing plant health problems, recognizing and understanding infectious plant diseases, integrated management of ornamental diseases, and an extensive section on descriptions and management options of the common diseases found in the landscape. The cost is $5.25 plus tax.
Bulletin 614 is available at all Ohio State University Extension county offices. Individuals living outside Ohio can contact the Extension Media Distribution Office at 385 Kottman Hall, 2021 Coffey Road, Columbus, Ohio 43210-1044, call 614-292-1607, or fax 614-292-2270 to order. There will be a shipping charge.
The extended cool, wet conditions this spring as leaves of many trees were emerging and expanding resulted in greater incidence and severity than normal of the many different anthracnose diseases. With syca-more anthracnose, these conditions resulted in symptoms much more severe than the blotchy reddish discoloration along leaf veins that are commonly seen in periods of mild disease incidence. Severe infections resulted in the types of symptoms described in Bulletin 614:
"New leaves may be killed. Damage looks similar to frost injury. Older or mature leaves show small to large, irregular dead areas along the veins. In the spring, bud blight and twig cankers occur with some dieback. The lower portions of the tree are damaged more severely. Crooked branches and a witches-broom-like proliferation of twigs are also common symptoms. Defoliation occurs after leaf blight in the spring."
Fortunately, most of these sycamores recovered, with refoliation by late June, but early symptoms were severe.
Abnormally severe symptoms were also noted on white oaks throughout Ohio and the Midwest. There was an excellent description of this in the Purdue Educator Update, reprinted below:
"We recently received a sample of white oak with succulent growth from Warsaw, Indiana, that was confirmed to have anthrac-nose. Oak anthracnose usually shows up as a lighter tan discoloration on the margins and midribs of oak leaves, causing distortion of the leaves. The infected tissue on the oak leaves we just received was black, not tan! This could be due to the extended wet weather and the succulence of the young tissue. The use of chemicals is generally not warranted for managing anthracnose of shade trees in homeowner yards."
Anthracnose diseases were also common this year on ash, London plane (less severe than on sycamore), beech, maple, and dogwood. In most cases, plants recovered once warmer drier conditions prevailed, although major plant health problems did occur on flowering dogwoods affected by anthracnose caused by Discula destructiva.
Cool, wet weather in the spring of 1996 and 1997 was highly favorable for infection and development of diseases in Scot's pine Christmas tree plantations. Samples received in the Plant and Pest Diagnostic Clinic (PPDC) included Cenanagium canker, Diplodia (Sphaeropsis) tip blight, and Lophodermium and Cyclaneusma needlecasts. The most important was Diplodia (Sphaeropsis) tip blight (which is also a common problem on Austrian, red, and mugo pines in Ohio).
Cenangium canker (Cenangium sp.) was reported in Ohio on Scot's pine Christmas trees for the first time in 1996, and was again identified in Ohio in 1997.
Samples examined in 1997 exhibited dieback of branch ends and whole branches. Control recommendations include pruning to remove disease tissue, which unfortunately often results in an unsalable tree for a Christmas tree grower. Cenangium canker was observed on Tanyosho pine (Pinus densiflora cv. Umbraculifera) in Ohio for the first time in 1997. This disease typically affects weakened trees, so control strategies should focus on good overall tree health management practices.
Cyclaneusma and Lophodermium needlecasts of Scot's pine samples were commonly received in the PPDC. Samples sent to the Clinic should include branches with both intact needles on twigs (to check for brown spotting and tan-colored banding) and detached needles caught up in branch crotches (most likely to have identifiable fruiting bodies of the disease-causing fungus).
Needles collected from the ground are often colonized by so many fungi that identification of the disease involved is impossible. This is important because spray timing for Cyclaneusma control is in spring and into summer while for Lophodermium control, spray timing is for late summer and early fall. Other controls include planting in sites that are not shaded, promoting good air movement by thinning and pruning, and roguing out badly infected plants.
Diplodia (Sphaeropsis) tip blight of pine was again quite common and severe in landscapes and Christmas tree plantings and is described in this quote from Bulletin 614:
"Dieback of tips of Austrian, red, mugo, and Scot's pine. Disease often visible early in the season. Stem tips are killed before needles reach full size. Small, black fruiting bodies of the fungus develop at the base of needles and on the old cones. Resin may ooze from the diseased stem tips. Usually occurs on lower branches first." Management options: Where feasible, removal and disposal of diseased twigs may be helpful. If fungicides are used, spray just before new growth starts, followed by one or two more sprays at 14-day intervals. Use a properly labeled fungicide (such as thiophanate methyl in Cleary's 3336, Fungo and Domain). Fertilize and water trees when needed."
Additional diseases on pine included a confirmed case of Phytophthora root rot on white pine and branch dieback caused by Atropellis canker on Austrian pine.
On spruces, Rhizosphaera needlecast disease samples were sent in to the PPDC. The Rhizosphaera fungus infects new spruce needles during the growing season, but symptoms do not show up until needles exhibit yellowing late in the season. The following spring and summer, needles turn various shades of purple and brown and are noticeable as discolored second-year needles behind the green needles of the current season's growth. A characteristic of this disease is tiny black fruiting bodies of Rhizosphaera seen lined up on the otherwise whitish stomates on the needles, especially if the needles are put into a moist chamber for a few days (a plastic bag with wet paper towels will do). New infections can be prevented with applications of labeled fungicides (e.g., those containing chlorothalonil).
Cedar quince rust is caused by Gymnosporangium clavipes, a fungal species related to the fungi that cause more spectacular oozing galls associated with cedar apple rust and cedar hawthorn rust on junipers. As with the other cedar rusts, the fungus alternates living on Eastern red cedar (juniper) and a rosaceous host such as apple, crabapple, hawthorn, the occasional quince, and others.
Generally, little attention is paid to cedar quince rust on juniper. Instead, the orangish spore masses that later in the summer protrude from hawthorn fruits and swollen areas on stems are noticed. However, there are symptoms on juniper.
Quoting from Bulletin 614: "(There are) slight swellings on stems and twigs of susceptible junipers. The affected twigs are hardly noticed until yellow-orange, jelly-like spore masses form in late April and May. The twigs may die back."
In 1997, however, the PPDC received samples of certain junipers with dozens, if not hundreds, of cedar quince rust infections, including numerous swollen areas on stems from the disease. It was easily causing enough damage to make the plant ornamentally unsuitable with the considerable twig dieback present and was serious enough to significantly affect overall plant health in these cases. So, cedar quince rust can be a factor not only on the appearance of susceptible hawthorns, but also on the juniper host as well.
The two other common problems on junipers are Kabatina blight and Phomopsis blight. Both are covered extensively in Bulletin 614, with some details repeated here. Quoting from Bulletin 614 on Kabatina blight:
"Symptoms first appear in February and March and well before those of Phomopsis tip blight. The terminal 2-6 inches of diseased branches throughout the juniper first turn dull green, then red or yellow. Small ash gray to silver lesions dotted with tiny, black fruiting bodies of the fungus are visible at the base of the discolored tissue. The brown desiccated foliage eventually drops from the tree in late May or early June. Foliar blighting occurs only in early spring; it does not continue through the summer {while it does continue with Phomopsis blight}. Blighting is also restricted to the branch tips and does not cause extensive branch dieback or tree death. The primary infection period for Kabatina blight is thought to be in autumn, even though visible symptoms are not apparent until late winter or early spring. Infection often is associated with small wounds on branch tips caused by insect feeding and mechanical damage."
Control involves cultivar selection for disease resistance (extensive lists in Bulletin 614), spacing plants for good air ventilation, limiting plant wounds, avoiding overhead irrigation if possible, and pruning of affected twigs during dry weather. Unlike Phomopsis, blight fungicides are not labeled for this disease.
Quoting Bulletin 614 for Phomopsis tip blight:
"Phomopsis damages new growth on succulent branch tips of junipers from April to September. Older, mature foliage is resistant to infection; therefore, most blighting occurs on the terminal 4 to 6 inches of the branches. Affected foliage first turns dull red or brown and finally ash-gray. Small gray lesions often girdle branch tips and cause blighted foliage beyond the diseased tissue. Small, black, spore-containing fungal fruiting bodies develop near the base of dead tips."
New infections will occur with flushes of new growth for some time, especially if plants are sheared. Fungicides containing thiophanate-methyl, such as Cleary's 3336, are often used as preventive sprays.
Reports and samples of this problem con-tinued in 1997. Typically only a portion of the foliage is affected and numerous causes are suggested, though follow-up research and observations remain sketchy. The most likely range of causes appear to be:
The authors would appreciate receiving samples, descriptions, locations, and follow-up reports of recovery or non-recovery relative to this problem in the future so that better understanding of what causes this blackening can be achieved.
Powdery mildew diseases were predictably common on many woody and herbaceous hosts in 1997, but two seem noteworthy due to the symptoms observed. Powdery mildew on flowering dogwood was again quite prominent this year, causing not only the familiar powdery fungal growth on foliage, but also distortion and curling of new shoots, and reddish foliar discoloration in some cases. Foliar browning and purpling were also noted on magnolia in response to powdery mildew infections.
For most of Ohio and at the Crabapple Evaluation Plots in Wooster, apple scab was moderate in severity, slightly below normal. However, there were some localized reports of severe scab this year (such as in the Mahoning Valley), including some "sheet scab" in which the entire leaf becomes colonized by the fungus in late spring. See the article on crabapples in this Special Circular (page 83) for five-year summaries of scab incidence on many common crabapple selections.
It was another good year for this disease and thus a tough one for rosarians. Infections started during cool, wet spring weather as leaves emerged. An integrated plant-health management program for this disease in the landscape includes:
A few examples from each of the rose categories with good genetic rose black-spot resistance (thanks to Deborah C. Smith-Fiola's "Pest Resistant Ornamental Plants," published by Rutgers University,) include:
Hybrid Teas: Chrysler Imperial, Tropicana
Floribundas/Grandifloras: Betty Price, Sonia
Shrub Roses: All That Jazz, Carefree Wonder
Miniatures: Gourmet Popcorn, Rose Gilardi
Rugosa Hybrids: Polyantha, The Fairy
This vascular disease occurs on many different landscape plants, as well as a number of fruits and vegetables. It is perhapes best-known as an ornamental disease on various species of maple. Some other plants that were identified in the PPDC as having Verticillium wilt in 1997 included black-eyed susan, purple coneflower (first report for Ohio), smoketree (Cotinus), yellowwood (Cladrastis), and garden impatiens.
There are several sampling tips that help ensure a good diagnosis in a lab. First, when possible, send parts of the plant that appear to be actively declining, rather than parts that are completely dead or completely healthy-looking. Second, for herbaceous material, such as with impatiens, send the entire plant. Third, remember that on some species of plants, the characteristic vascular discoloration is often not present even when the plants are infected, such as on ash, Japanese maple, and yellowwood.
This blight of horsechestnuts and our beloved buckeyes (both in the genus Aesculus) was frequently reported again this year. Symptoms are best described by quoting from Bulletin 614:
"Small to large irregular, reddish-brown spots with yellowish edges occur on leaves in late June to July. Spots enlarge with browning and curling of leaflets. The disease is more prevalent on lower leaves."
At many sites, the blotching often is so bad that plants look as if they were blow-torched by August. Starting in 1998, Ohio State University plans on "aesculating" its efforts to help answer the questions of species and cultivar resistance to this disease, comparative incidence and symptomatology of Guignardia blotch and non-infectious physiological leaf scorch and other studies.
The Ohio forest health report is provided in toto in this disease article, although it in-cludes not only infectious and non-infectious disease observations, but also insect damage.
"An aerial survey of Ohio's unglaciated hill country (an area south of a line from Belmont and Guernsey Counties to Adams County) was accomplished during late June. The five-million-acre survey did reveal 16 damage locations, 14 of which accounted for approximately 1,000 affected acres. The cause of every damaged site could not be accurately determined; however, ground checks did confirm flooding damage, pine sawfly damage, grazing damage, declining white pine, and anthrac-nose/lace bug damage to sycamore trees along riparian corridors. In addition, the survey indicated moderate defoliation/discoloration (browning) in the upper crowns of oak trees scattered throughout 40,000 acres in Adams, Gallia, Lawrence, and Scioto Counties. Telephone reports from property owners in these areas confirmed observations. Laboratory samples identified scarlet oak sawfly larvae and hickory tussock moth larvae skeletonizing the oak foliage. Scarlet oak sawfly larvae were probably causing the majority of the damage as they fed on black, scarlet, pin, red, and white oaks. Hickory tussock moth larvae were found feeding on chestnut and red oaks. Similar observations were reported by the West Virginia Department of Agriculture.
"Reports of white pine mortality continue to decrease, but 2 cases were documented in Jackson and Vinton Counties. Mortality is still being attributed to a complex of over-crowding, environmental conditions, and secondary insects and diseases. Yellow-poplar mortality was scattered throughout SE Ohio. The cause for this mortality is not fully understood; however, declining yellow poplar trees at Zaleski State Forest stopped growing after 1991 indicating that drought damage in the early 90s, followed by yellow poplar weevil damage, could be contributing factors. A 13-acre salvage harvest was implemented to remove dead and dying yellow poplar trees from one Zaleski stand.
"Mortality of swamp white oak, pin oak, and red oak in NW Ohio woodlots was reported again this year. The cause of mortality has not been established; however, regional reduction in ground water levels is suspected. Some oak mortality occurred at Maumee State Forest, resulting in salvage harvests totaling about 90 acres.
"Cherry scallop shell moth defoliated black cherry trees on 565 acres in the following counties: Guernsey (225), Harrison (140), Jefferson (110), and Columbiana (90). Dogwood anthracnose was reported across Ohio, but was not verified in any new counties. Beech bark disease was not found in 1997. Frequent reports were received of anthracnose diseases (ash, maple, oak, dogwood, sycamore), Diplodia tip blight (Austrian and Scot's pine), fall webworm (cherry, apple, crabapple, walnut), and locust leaf miner (black locust). This is the second consecutive year to receive a few reports of bald cypress webworm feeding on bald cypress trees in western Ohio. Elm yellows (red elm and American elm) was also prevalent in at least 7 Ohio counties this year."
Each year the Ohio Department of Agriculture (ODA) compiles a list of the top diseases that are reported by ODA inspectors in their nursery inspections each year. The ODA list of the top 15 diseases appears here along with the number of times each disease was reported by inspectors.
Note: This list is not a rating of the most important or damaging ornamental diseases. It is, however, a list of common diseases, all of which you should be able to identify. If you cannot, 1998 is the year to learn.
A number of first reports of diseases in Ohio this past year were confirmed in the PPDC.
This disease causes a blighting and flagging of young shoots. Presumably the infections started in the flowers and moved back into young stems. The tell-tale signs of this disease are the development of hardened fungal sclerotia enmeshed in powdery white fungal growth inside the pith of the stems. This uncommon disease (for this host) should not be confused with the buckeye petiole borer that causes flagging of individual leaves of certain buckeyes.
This disease was positively identified using ELISA enzyme immunoassay on roots from a declining white pine in a landscaping in southwest Ohio. The arborist who sent the sample suspected a number of possible problems including deterioration simply due to heavy soil and/or poor drainage. While those factors probably predisposed the tree for infection, the Phytophthora fungus was functioning as a microscopic, soil-borne Dr. Tree-Vorkian and finished the job of killing the tree.
Three samples of Harry Lauder's walkingstick (Corylus avellana cv. 'Contorta') were received in the PPDC during 1997. Samples were exhibiting branch dieback. These were determined to be infected with eastern filbert blight, a fungal disease, which causes extensive cankering and dieback. Fruiting structures of this fungus occur in rows along the length of the affected branch.