BYGL Weekly News for September 3, 2018
The following articles were compiled during the last 7 days by members of the Extension, Nursery, Landscape, Turf (ENLT) team to benefit those who are managing a commercial nursery, garden center, or landscape business or someone who just wants to keep their yard looking good all summer. Access the BYGL website for additional information on other seasonal topics at: http://bygl.osu.edu
For more pictures and information, click on the article titles. To contact the authors, click on their names.
Authors Joe Boggs
Published on August 31, 2018
The long-term outlook for eastern black walnuts (Juglans nigra) seemed dire when the Thousand Cankers Disease (TCD) complex was confirmed in Butler County, OH, in 2013. Thankfully, TCD has not followed the devastating trajectory we originally feared. It is not rolling through our native black walnuts à la emerald ash borer (Agrilus planipennis) rolling through our native ash. The two situations are like apples-to-oranges.
However, there have been some recent reports of Ohio landowners being approached by misinformed timber buyers and loggers citing TCD as a reason to cut and sell walnut trees. There is no support for the pre-salvage harvesting of walnut trees.
Rather than following unsolicited advice, landowners should talk with a professional forester of their choosing before planning any timber harvest including the possible harvest of high-value black walnut trees. The “Ohio Call Before You Cut” is a great resource ((877) 424-8288). See “More Information” below for the website.
The TCD complex involves a phytopathogenic fungus, Geosmithia morbida (Gm), carried from tree-to-tree by the Walnut Twig Beetle (WTB), Pityophthorus juglandis, which is a type of bark beetle. Both are found naturally in walnuts native to the southwest U.S. such as Southern California black walnut (J. californica) and Arizona walnut (J. major). However, since the trees, beetles, and fungus co-evolved, TCD does not kill these trees.
Such is not the case with eastern black walnut since it did not co-evolve with the TCD complex. It is generally accepted that unprocessed wood from eastern black walnuts planted in the southwestern U.S. served as vehicles for the TCD complex to hitchhike to other locations in the U.S. Although the exact route is unknown, it eventually arrived in Ohio.
As is common with bark beetles, WTB attacks its host’s stems in multiple locations with the females boring through the bark and tunneling through the phloem. The Gm fungus carried by the beetles infects the surrounding phloem tissue producing small circular to oblong shaped dark brown cankers in the phloem tissue. TCD is so-named because of the collective impact of multiple cankers: “death by a thousand cuts” becomes death by a thousand cankers.
Despite its common name, WTB actually targets branches that are greater than 1/2″ in diameter. They will also tunnel into the main stems. The adult and larval tunneling and feeding activity produce symptoms typical of bark beetles with frass-filled galleries meandering through the phloem.
Traps baited with an aggregation pheromone that attracts both male and female WTBs have been available for a number of years. They have been successfully used to detect new WTB infestations in the U.S. as well as evaluating the population densities and the spread of known infestations.
WTB was first detected by traps in Ohio late in 2012. Thanks to a report from an alert landowner, infested and infected trees were found in August 2013. Trap counts were impressively large within the TCD site. For example, the beetle catch shown in the image below was over 1,000 beetles caught in one week. This caused us all to believe TCD was a clear and present danger to our native black walnut trees.
However, in 2014, beetle trap catches dropped off dramatically and have remained low ever since. Only 1 beetle was caught last year in multiple traps deployed to evaluate beetle populations in Ohio. A similar dramatic drop in trap catches was observed that same year in eastern Tennessee where a much larger WTB infestation had been found some years before. In fact, many heavily infested trees in Tennessee that were expected to die have recovered.
The reason for the sharp decline in beetles as well as the intensity of infections is not entirely known. However, research conducted by University of Minnesota graduate student Andrea Hefty for her Ph.D. thesis revealed that WTB has low-temperature survival thresholds for both the adults and larvae. Some have speculated that the southward shift in the North Polar Vortex during the 2013-14 winter season may have produced temperatures that crossed those thresholds.
Of course, black walnuts trees aren’t out of the woods yet. Even though beetle trap catches are low, they aren’t zero. There is always a chance beetle populations could rebound which is why Butler County, OH, remains quarantined. Movement of walnut trees as well as wood products such as logs cannot be moved outside of the county within Ohio, or outside of the state, without conforming to quarantine restrictions. For details, contact the Ohio Department of Agriculture (ODA).
Observe and Report
The possibility that TCD could rise again is why we must remain vigilant not just in Butler County, but elsewhere in Ohio. Symptoms of TCD include yellowing foliage (chlorosis) that progresses rapidly to brown wilted foliage, and finally branch dieback. Infected trees develop thinning canopies and top dieback with epicormic growth sometimes sprouting from lower portions of main stems.
Unfortunately, walnut anthracnose produced by the fungus, Ophiognomonia leptostyla, may be mistaken for symptoms of TCD and vice versa. This is particularly important to keep in mind since the annual dropping of walnut leaflets and leaves due to anthracnose is well underway in southwest Ohio. The fungus is specific to black walnut. Unlike some of the other anthracnose diseases, walnut anthracnose is characterized by small dark brown spots rather than the larger irregularly shaped necrotic lesions seen with ash or oak anthracnose. The spots are responsible for the alternate common name for the disease of walnut black spot.
However, don’t rely entirely on the images I’ve provided in this report to eliminate TCD from a diagnosis. If you suspect TCD is affecting a walnut tree, you should contact our ODA. It’s always better to report a suspected occurrence of TCD even if it turns out not to be rather than to ignore an actual TCD site out of fear of being wrong. Remember that TCD in Ohio was originally discovered thanks to an alert landowner contacting our ODA!
Call Before You Cut
Authors Joe Boggs
Published on August 28, 2018
When you read or hear about “Asian hornets,” you need to keep two things in mind. First, the “Asian” moniker has been commonly applied to at least three hornet species native to various Asian regions. These include the Yellow-Legged Hornet, which is sometimes called the Yellow-Legged Asian Hornet (Vespa velutina); the Asian Giant Hornet (V. mandarinia) which is the world’s largest hornet; and the Japanese Hornet which is a subspecies (V. mandarinia japonica).
The second thing to remember is that none of these hornets have been found living in the U.S. in spite of what you may find posted online. However, this does not mean we shouldn’t be vigilant. The yellow-legged hornet was discovered in France in 2004 and has spread into a number of other European countries. It was found in Great Britain’s Channel Islands in 2016.
It’s a significant accidental introduction because this species, as well as the two other Asian species, behave as predators; they kill other insects and can wreak havoc on honey bee hives. If you suspect that you’ve run across one of the Asian species, contact your state’s agricultural regulatory agency for instructions. Official positive identification requires preserved specimens. Frozen specimens are ideal if you can safely collect and freeze the suspects.
Cases of Mistaken Identity
Photographs cannot provide official positive identifications of a non-native Asian hornet; however, they can still be very useful. I always recommend snapping some pictures and sending them to the appropriate entomology experts in your state. I’d be happy to take a look at them if you’re in Ohio.
The two insects most commonly mistaken for Asian hornets are European hornets (V. crabro) and our native cicada killer wasps (Sphecius speciosus). Cicada killers are the largest native wasp found in Ohio. Their activity usually starts winding down at this point in the season; however, both the wasps and their robust namesake food item, dog-day cicadas (Tibicen spp.; family Cicadidae), remain in full-swing in southwest Ohio.
European hornets were first found in the U.S. in New York State around 1840. Since that time, the hornets have spread to most states east of the Mississippi and a few states to the west. European hornets are impressively large, measuring 1 – 1 1/4″ in length. Their black and yellow markings on their abdomen make them look like yellowjackets on steroids; however, their head and thorax have distinct chestnut-colored markings. Yellowjackets have black and yellow markings on the head and thorax.
Technically, this non-native is the only “true hornet” found in Ohio. Taxonomically, our native bald-faced hornets (Dolichovespula maculata) are not hornets; they are grouped with yellowjackets which is why they are in the same genus as native Aerial Yellowjackets (D. arenaria).
Unlike our native yellowjackets and wasps, European hornets can cause noticeable girdling damage to twigs and branches of trees and shrubs by stripping bark to the white wood. It is speculated that the hornets are extracting sugar from the phloem tissue. Although the damage may be noticeable, it’s seldom significant enough to cause concern.
European hornets construct paper nests that may look similar to the bald-faced hornet nests. However, they are most often found in hollow trees and sometimes in the walls of homes.
Normally, European hornets overwinter just like our native bald-faced hornets, paper wasps, and yellowjackets with only the queens that are produced this season surviving the winter. The new queens leave the nests to seek protected overwintering sites; old nests are not re-used. However, occasionally the entire European hornet nest will survive the winter if they are sufficiently protected. Indeed, although it is rare, nests in Ohio have been observed surviving through three winters.
European hornets are reputed to be highly aggressive and their large size does make them look pretty scary. However, during past encounters with this hornet, I was able to take close-up images and move branches with hornets on them without being stung or even charged. Still, landscapers should be cautious around these large stinging insects. Like wasps and yellowjackets, they are capable of stinging repeatedly.
The hornets may also fly at night and are attracted to porch lights or lights shining through windows. They have been known to repeatedly charge windows at night inducing panic in homeowners.
Beware of the Web
Unfortunately, there are numerous spurious web reports of giant Asian hornets swarming through multiple U.S. states. I do not believe these are intentional “fake news” reports; I believe most are cases of misidentifications or misunderstandings.
For example, you can find several online reports of the Asian stingers being found in Jersey. That’s not New Jersey but one of the Channel Islands, officially the Bailiwick of Jersey in the English Channel. It’s easy to miss such nuances while scanning web headlines.
Authors Cindy Meyer
Published on August 28, 2018
Japanese stiltgrass was not on my radar until a recent visit to a local park. It had piqued my interest because of the lushness of the plants beneath a full canopy of trees. My first thought was, what is this grass that could be a recommendation for shady sights? My excitement quickly waned because our hosts explained that the annual grass unfortunately, is considered an invasive species. In fact, this non-native species from Asia, which was first found in Tennessee in 1919, can produce up to a 1000 seeds per plant and crowds out native plants. The seeds from this plant are dispersed by a number of mechanisms including foot traffic, water movement, equipment, and wildlife.
Japanese stiltgrass (Microstegium vimineum) can be found in disturbed areas such as; edges of fields, forests, ditches, recreational trails, etc. It grows in low-light environments with sufficient soil nutrients and moisture but it can also adapt to low-nutrient and low-moisture areas with adequate light.
Japanese stiltgrass leaves are flat, pale green, asymmetrically lance-shaped, and about 1–3 inches in length. Leaves are sparsely hairy on both sides and along the margins. A shiny, off-center, mid-rib is conspicuous on the upper surface, which is sometimes described as a silver stripe, and is a distinctive identification feature. Leaves are arranged alternately along the branched stem and project outward. Spikelike flowers up to 3 inches long develop in late summer or early fall in the axils of the leaves at the tip of the stem. A shallow and fibrous root system is a distinguishing characteristic that sets it apart from the native white grass (Leersia virginica), which has a stout rhizome.
Managing for Japanese stiltgrass is not unlike managing for other invasive plant species. It requires diligent, hard work! Inspection of equipment such as mowers, road maintenance equipment, and timber harvesting is important. Cleaning and sanitizing equipment with known stiltgrass infestations helps to prevent spreading of this grass. Hand-pulling is effective late in the season before plants flower. Pulled plants should be bagged. Mowing and/or weed eating is also effective if done before the plants mature and go to seed. Chemical control with non-selective herbicides, non-selective pre-emergent herbicides and selective grass-specific herbicides can be effective but may require more than one application over the course of a few years. When using any chemical always read and follow label instructions.
Ohio State University Extension – Ohioline Factsheet
Rutgers – Japanese Stiltgrass Control in the Home Lawn and Landscape
University of Maryland Extension – Home & Garden Information Center
Published on August 27, 2018
A baldcypress broom: no not a description of my hairstyle. Secrest Arboretum Curator Jason Veil and moi were at the Harper’s Collection of Dwarf Conifers at Hidden Lake Gardens of Michigan State University this past weekend. We of course looked at the Taxodium distichum ‘Secrest’ cultivar, but Jason also called me over to a lovely ‘Cody’s Feathers’ specimen, and pointed out what I certainly did not know – that it was originally spotted outside the Wayne County Hospital in Wooster.
Who ya gonna call? Well, how about he who found it there, lo a decade and a half ago: Bill Bargar of Wadsworth, a longtime member and website and newsletter writer for the American Conifer Society. We called Bill for background and a few wonderful pictures.
“Witch’s brooms” are strange, condensed, short-internode proliferation of shoots within the more typical growth of the plant, in this case a baldypress. Many factors can cause broom-like growth but if caused by stable factors (such as a stable genetic mutation), then horticulturists see if they can usher a new version of the plant into the plant-lover world.
Bill who collected this broom, propagated it, and had it registered as a unique variant, the cultivar ‘Cody’s Feathers’, the cultivar name arising from his son’s description of the appearance of the feathery growth. Bill then grafted the cuttings to a compatible baldcypress rootstock.
This cultivar differs from other baldcypress brooms in its habit: as Jason describes it ‘Cody’s Feathers’ has a dense, shrub-like rounded habit that is unique. You can see this in Jason’s pictures from Hidden Lake. Bill’s images include a mature specimen at J.C. Raulston Arbortum at North Carolina State University, and the deep bronze-red color of foliage, highlighted in contrast to the blue-green cones.