Joseph F. Boggs
David J. Shetlar
Gary Yu Gao
Daniel Balser
Douglas C. Caldwell
Randall H. Zondag
James A. Chatfield
Joseph F. Boggs, Ohio State University Extension-Hamilton County; David J. Shetlar, Ohio State University Extension/Ohio Agricultural Research and Development Center/Entomology; Gary Yu Gao, Ohio State University-Clermont County; Daniel Balser, Ohio Department of Natural Resources Division of Forestry; Douglas C. Caldwell, Davey Tree Co.; Randall H. Zondag, Ohio State University Extension-Lake County; and James A. Chatfield, Ohio State University Extension-Northeast District/Horticulture and Crop Science
The following is a collection of notable plant insect pest problems observed in Ohio during the 1995 growing season. The information was based on reports made in the Ohio State University Extension's Buckeye Yard and Garden Line (BYGL), in David J. Shetlar's Pest Evaluation and Suppression Techniques (P.E.S.T.) Newsletter, and on other observations.
Weather conditions can have a significant effect on insect development, pest population levels, and pest/host relationships. From Dave Shetlar's P.E.S.T. summary for the year comes this observation:
"We came into the spring after a fairly mild winter but someone forgot to turn off the rain in May, June, and early July. Rain in the southern two-thirds of Ohio caused soils to become saturated and the roots of plants (whether trees, shrubs, or turf) were severely damaged. [Parts of] Northern Ohio got a drought.
"In mid-July, the faucet was abruptly turned off in some areas. However, hot humid conditions continued throughout August and early September. [Turf, trees, and shrubs] didn't have a very good root system in mid-July, and many plants couldn't survive the drought without roots. The result -- disease, borers, and grubs had their way with the plants."
Infestations of beetles which bore beneath bark or into wood were commonly reported this season. Such infestations have long been associated with plant stress. For example, the Columbian timber beetle (Corthylus columbianus) was found excavating oviposition tunnels in the limbs and main trunks of bigleaf magnolias in southern Ohio. This bark beetle was considered a secondary problem -- the magnolias were suspected of having Verticillium wilt disease.
Honeylocust trees came under heavy attack this season from honeylocust plant bug (Diaphnocoris chlorionis), potato leafhopper (Empoasca fabae), mimosa webworm (Homadaula anisocentra), and the honeylocust spider mite (Eotetranychus multidigituli). The onslaught caused concern regarding increased risk of infestation by the honeylocust borer (Agrilis difficilis). Dave Shetlar noted in BYGL 95-11:
"Trees subjected to stress-causing factors, such as heavy [insect] feeding, are more susceptible to attack by borers. Therefore, to protect damaged honeylocusts from borers, arborists may consider making an application of an EC formulation of chlorpyrifos (e.g., Dursban). Applications should be made to trunks and special attention should be given to recently planted honeylocusts."
This form of preventive application was also recommended for control of twolined chestnut borer (Agrilis bilineatus) in recently planted oaks. From BYGL 95-8: "This application should be done the first two years after planting and is more critical on trees that are in high profile areas and are suffering from planting-induced stress."
Bark beetles did not spare conifers this season. Dave Shetlar noted in his P.E.S.T. summary: "Conifer bark beetles also continued to make use of stressed pines, spruces, and white cedar. Of course, again, the real problem was root rots and poor growth due to excessively wet and dry soils as well as fungal diseases. When these agents weaken the tree, it becomes defenseless because it can not muster enough sap to gum up a borer trying to enter through the bark. Unfortunately, when these bark beetles attack, the plant is probably history. Surrounding conifers should be evaluated for their health -- color and amount of growth. If they are also showing signs of stress, protectant bark sprays may be warranted in mid-May and again in mid-July, the time that most conifer bark beetle adults are searching for stressed trees. Use lindane or chlorpyrifos (=Dursban)."
Gregarious-feeding caterpillars, such as the yellownecked caterpillar (Datana ministra), walnut caterpillar (D. integerrima), and the hickory tussock moth (Lophocampa caryae) were common throughout Ohio. However, no serious outbreaks were reported.
Large solitary-feeding caterpillars were also common, and some provided exciting human encounters. One of the most impressive looking (and named) is the hickory horned devil (= regal moth) (Citheronia regalis). Measuring 4-6 inches in length, this aggressive, hairless, blue-green caterpillar has long, curved, orange spines (with black tips) on the first two thoracic segments and three to four shorter black spines on the top of each additional segment.
Its common name comes from its preferred host -- hickory -- and from its behavior. When disturbed, the devil whips its head and thorax around, giving the convincing impression that it is trying to impale the offending irritant. The caterpillar also feeds on sumac, sweet gum, and walnut.
Populations of yellow jackets (Vespula sp.) were unusually high in several areas of the state this year. It was noted that caterpillars such as the yellownecked caterpillar and fall webworm (Hyphantria cunea) seemed to be vanishing in areas where yellow jackets were most numerous. Yellow jackets were observed "picking off" these caterpillars and thus appeared to be orchestrating the caterpillar disappearing act. Where yellow jacket populations were low, caterpillars remained quite noticeable.
The locust leafminer (Odontota dorsalis) ravaged black locust leaves throughout Ohio. The digitate mines produced by the larvae, coupled with the skeletonized leaves produced by the adults, caused many trees to become completely brown. Birch leafminer (Fenusa pusilla) was common, but populations appeared to be lower than last year.
Lacebug populations developed slowly this year due to heavy rains in the spring and early summer. However, once rains subsided in July, populations expanded rapidly. Damage was noted on azalea, rhododendron, cotoneaster, and amelanchier with the heaviest injury occurring on hawthorn and oak.
By mid-August, the oak lacebug (Corythuca arcuata) had stippled leaves on bur and chestnut oaks in southwest Ohio almost to the point of transparency. At about the same time, similar damage produced by the hawthorn lacebug (C. cydoniae) was observed on hawthorns in northeast Ohio.
European pine sawfly (Neodiprion sertifer) made an unusually early spring appearance on hard pines in southern Ohio. Eggs hatched in early April. Last year, egg hatch did not occur until late April for central and southern Ohio. The early appearance was attributed to the uncommonly mild winter.
Redheaded pine sawfly (N. lecontei) made its usual appearance in mid to late summer and white pine sawfly (N. pinetum) came on the scene in early to mid-fall. Although all three sawflies were common, populations appeared to be lower this year.
After being frozen out during the winter of 1993-1994, bagworm (Thyridopteryx ephemeraeformis) made a comeback this season. From Columbus south, this pest was common on junipers, white pine, spruces, and a variety of broadleaf trees.
Although the last brood of the periodical cicada, or 17-year cicada (Magicicada septendecum), emerged several years ago in Ohio, branches are still succumbing to the old slit-like oviposition scars produced by females of this insect. Leaves were observed wilting and turning brown this season on heavily scarred branches of several deciduous trees including birch, oak, and hickory. Expression of symptoms so long after the injury has occurred can present a serious diagnostic challenge.
Dan Balser of the Ohio Department of Natural Resources (ODNR) Division of Forestry summarized a number of reports from ODNR foresters throughout Ohio. These included defoliation of 30 acres of trees by the cherry scallop shell moth (Hydria prunivorata) in Columbiana County, reports of beech scale (Cryptococcus fagisuga) on American beech in northeast and eastern Ohio, heavy cottony maple scale (Pulvinaria innumerabilis) infestations at several urban sites on silver maple, lighter pear thrips (Taeniothrips inconsequens) damage on maples than in recent years, and heavier pine bark adelgid (Pineus strobi) infestations than usual reported from northern Ohio.
Doug Caldwell of Davey Tree notes that several lecanium scale species (such as Parthenolecanium corni) developed very heavy populations in northeastern Ohio on a number of hosts, including oak, sweetgum, and maple. Doug waxed poetic, describing the massive overlapping infestations thusly: "Like barnacles on the hull of a ship, complete with ghost rain and sooty mold."
Grub reports were made in nine of the 27 BYGLs this year -- it was an interesting grub season. The BYGL season led off with a report in BYGL 95-1 concerning the efficacy (or lack thereof) of spring grub applications:
"Dave Shetlar indicated that spring applications are generally not recommended for Ohio: Overwintered Japanese beetle (Popillia japonica) and northern masked chafer (Cyclocephala borealis) grubs move up and down in the soil profile making exposure to insecticides inconsistent; grubs are large (Chuck Behnke, Lorain County calls them "Bubba Grubs") making them more difficult to kill; overwintered grubs cause little damage -- most damage occurs in the fall. Dave noted that spring applications seldom have more than a 50 percent efficacy rate."
Japanese beetle adult emergence proceeded slowly this year due to delayed larval and pupal development this spring. Developmental rates were prolonged because of the extended cool weather conditions. Consequently, adult feeding activity -- and the accompanying damage -- occurred over an extended period of time. For example, Dan Balser (Ohio Department of Natural Resources) reported in the August 24, 1995, BYGL (BYGL 95-21) that skeletonized basswood leaves in northwest Ohio were just beginning to turn brown.
Although adult emergence was prolonged, the timing for white grub control applications was not radically affected. The grub control application window opened around mid-August. Dave Shetlar reported in BYGL 95-19 (August 10, 1995): "Japanese beetle larvae (grubs) are in the late first instar stage, and northern masked chafer larvae have reached the early second instar stage in central Ohio. Although adults of both beetles are still being seen, the majority of the eggs for this season have been laid. This means that NOW is an ideal time to make grub applications in southern and central Ohio. Next week will be ideal for northern Ohio."
Challenges associated with differentiating white grubs from other root-feeding insects, such as black vine weevil (Otiorhyncus sulcatus), in nurseries and landscaping was of particular concern this season. For example, the following is from a BYGL-25 report titled, "Grubs or Black Vine Weevil Larvae?"
"Randy Zondag reported serious grub problems in landscaping and containerized nursery stock. Although grubs are often only considered in relation to turf, Dave Shetlar pointed out that Asiatic garden beetle (Maladera castanea), Oriental beetle (Anomala orientalis), and European chafer (Rhizotrogus majalis) grubs can do very well on the roots of woody ornamentals. Currently, these beetles are found only in Northeast Ohio.
"Root feeding by these grubs produces damage which is very similar to that caused by black vine weevil (BVW) larvae. Also, BVW larvae are 'grub-like' and can currently be found feeding on roots. However, control strategies for BVW and the grub-producing beetles differ (see OSU Extension Fact Sheet 1026-88, 'Black Vine Weevil and Its Control.' Thus, grub identification is very important. BVW larvae do not have a discernible raster pattern on the underside of the tip of the abdomen. The Asiatic garden beetle, Oriental beetle, and European chafer beetle grubs do have raster patterns and this feature is used to identify the grubs. Refer to OSU Extension Fact Sheet HYG 2510-94, 'Identification of White Grubs in Turfgrass' for diagrams of the raster patterns."