BYGL Weekly News for September 2, 2019
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
To receive immediate email notifications when articles are published by the BYGL writers. Send an email to bygl-alert@lists.osu.edu using the phrase “Subscribe to BYGL ALERTS” in the subject line.
For more pictures and information, click on the article titles. To contact the authors, click on their names.
Authors Amy Stone
Published on August 30, 2019
Check out the most recent Turfgrass Times recorded August 30, 2019. This session includes updates from Dr. David Gardner; Dr. Ed Nangle; Joe Rimelspach; Dr. Dave Shetlar (aka the Bug Doc); and Dr. Pam Sherratt.
There will be bi-weekly updates in September and a final update for the year in mid-October before Turfgrass Times for 2019.
White Masses on Stems of Redbud
Authors Joe Boggs
Published on August 27, 2019
Small, sticky, snowy-white masses are appearing on the stems of redbuds (Cercis canadensis) in southern Ohio. They could easily be mistaken for soft scales, mealybugs, or insect egg masses. However, they are the “egg plugs” of a treehopper originally named the Two-Marked Treehopper (Enchenopa binotata, family Membracidae).
The treehopper females use their sharp, saw-like ovipositors to cut slits in the bark of their host trees and insert eggs into the stems. They cover the bark wounds with the white, sticky egg plugs presumably to protect the eggs. The plugs also contain a chemical attractant that draws other females to lay their eggs in close proximity to one another. Eggs are laid in late summer and there is one generation per season.
The treehopper lays eggs on a wide range of hosts beyond redbuds. In fact, their egg plugs may be found on the stems of 15 plant species across 8 plant orders. This includes American bittersweet (Celastrus scandens), black locust (Robinia pseudoacacia), hickory (Carya spp.), tuliptree (Liriodendron tulipifera), viburnums (Viburnum spp.), wafer-ash (Ptelea trifoliata), and walnuts (Juglans spp.)
A Complex Story
Oviposition on a wide range of hosts is not unusual. However, it was eventually discovered that the exact “version” of the two-marked treehopper depended on the host. In other words, each of the hosts boasts its own two-marked treehopper. For example, the two-marked treehopper on redbud is specific to redbud; it does not occur on any of the other hosts. The treehopper on wafer-ash is confined to wafer-ash; the one found on black walnut is only found on black walnut, and so on.
The treehoppers are now collectively referred to as the “two-marked treehopper species complex,” or the “Enchenopa binotata complex,” or simply the “Enchenopa complex.” When referring to hoppers found on a specific host, authors will sometimes assign the plant genus to the scientific name. For example, the two-marked treehopper found on redbud is sometimes written as Enchenopa binotata ‘Cercis ‘.
A Song and Dance Man
Male two-marked treehoppers entice females by vibrating on plant stems and leaves to produce a “come hither” vibration detected by the females using specialized structures on their legs. Using sophisticated voyeur equipment, researchers have listened-in and discovered the males on one plant host produce entirely different vibration patterns compared to males on other hosts; they sing a different tune.
Regardless of the host, all of the treehopper variants look the same and practice the same egg-laying behavior. However, their life-cycles vary based on the host. Researchers have found that egg hatch in the spring is tied to sap flow. The eggs laid on one host species may hatch at a different time compared to those on laid on another host species depending on when the sap begins to flow for the two species. This out-of-sync development may have helped drive the divergence, but other factors may also have played an important role.
In fact, the driving forces behind the development of multiple variants of the two-marked treehopper have been the subject of a number of scientific papers. One of my favorite titles, “You stay, but I Hop: Host shifting near and far co-dominated the evolution of Enchenopa treehoppers.” I’ve included links to this and a few other papers under “More Information” below.
No Control Needed
Oviposition by the two-marked treehoppers appears to cause no appreciable harm to the tree hosts; stem dieback has not been observed with this insect. While the strikingly white egg plugs are often very evident, particularly on wet stems, the foamy exudate doesn’t last long.
Although both the adults and nymphs suck juices from leaf veins and petioles, their feeding damage is also considered inconsequential even when high populations occur. So, control of these treehoppers is not generally required.
More Information
2010 Host shifts and signal divergence: mating signals covary with host use in …
https://cocroft.biology.missouri.edu/wp-content/uploads/2014/07/2010-Cocroft-et…
2015 Variation in signal–preference genetic correlations in Enchenopa treehoppe…
https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.1567
2017 You stay, but I Hop: Host shifting near and far co-dominated the evolution…
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ece3.3815
Authors Joe Boggs
Published on August 26, 2019
This is the third BYGL Alert! this season that focuses on Fall Webworm (Hyphantria cunea). This Alert is in response to the numerous e-mail reports I’ve received of spectacularly large silk nests occurring in southwest Ohio. They are most likely the work of the red-headed fall webworm biotype.
You can read the past postings including the Alert on the rise of second-generation caterpillars by clicking on these hotlinks:
https://bygl.osu.edu/node/1292
https://bygl.osu.edu/node/1372
Our native fall webworms have two biotypes named for the color of their head capsules. The black-headed biotype has black head capsules. Nest produced by the caterpillars of this biotype appear to include caterpillars from only a few egg masses. The nests tend to be small and compact usually enveloping only a dozen or so leaves. However, several of these small communal nests may be found on the same branch.
Red-headed fall caterpillars are far more cooperative; their communal nests may include caterpillars from a large number of egg masses. Thus, they can produce some truly spectacular multilayered nests enveloping the leaves on entire branches. This biotype is the more damaging of the two.
Historically, red-headed fall webworms were confined to the northeast and eastern parts of Ohio and black-headed webworms were found elsewhere in the state. However, in 2016, I found the red-headed biotype in a Hamilton County park near the Ohio-Indiana border. Since then, this biotype has expanded its local geographical range to include several counties in the southwest part of the state.
Fall webworms have a very wide plant host range with their silk nests recorded on over 400 species of trees and shrubs. However, penetrating the webworm’s dense silk nests with topical insecticides, particularly second-generation nests, is problematic.
The insecticide option is seldom justified for managing fall webworms. First, there are over 50 species of parasitoids and 36 species of predators known to make a living on fall webworms. They are the primary reason year-to-year fall webworm populations can rise and fall dramatically. Indeed, insecticides may kill these bio-allies preventing them from positively influencing the population dynamics of their webworm prey.
Second, fall webworms seldom cause significant injury to the overall health of established host trees. Most of the damage is done by the second generation. Their late-season defoliation occurs after trees have acquired enough carbohydrate to support next season’s leaf expansion. This includes the potential damage caused by the large nests produced by red-headed webworms.
2-Step Digital Management Demonstration
Given the limited impact of fall webworm on overall tree health coupled with the high impact of bio-allies, a perfectly valid management option for established trees is to do nothing. Recently planted trees are a different matter. Thankfully, silk nests on small trees are usually within easy reach.
Julie Molleran (Horticulturist, Spring Grove Cemetery and Arboretum) demonstrates the 2-Step Fall Webworm Digital Management Technique. This approach is in keeping with Spring Grove’s dedication to using all facets of Integrated Pest Management (IPM).
Julie is taking advantage of several fall webworm behavioral characteristics to maximize impact. First, both red-headed and black-headed fall webworms only eat leaves that are enveloped by their silk; they never leave their nests. In fact, the caterpillars are well-equipped for life on the web. Their long hairs aid the caterpillars in remaining positioned within the webbing with their hairs folding backward making them look like they’re “swimming” through their webs.
Second, webworm caterpillars are often found grouped together in dense clusters making it handy to remove the whole colony with a single swipe. The entire silk nest does not need to be removed other than for aesthetic reasons.
Using pruners to cut out nests is not needed unless nest removal fits with overall pruning plans. Of course, setting fire to the silk nests is highly discouraged unless there is a desire to deal with the severe bark injury produced by 1,000+ F. temperatures.
As Julie demonstrates, physically removing webworm caterpillars coupled with the “caterpillar stomp” is a highly effective management option. Thus far, no populations have become resistant to this IPM tactic.
Authors Amy Stone
Published on August 26, 2019
Source of Information for this Alert – USDA APHIS, Rhonda Santos
August is the height of summer, and it is also the best time to spot the Asian longhorned beetle (ALB) as it starts to emerge from trees. The U.S. Department of Agriculture (USDA) is asking the public to take five minutes to step outside and report any signs of this invasive pest. Checking trees for the beetle will help residents protect their own trees and better direct USDA’s efforts to eradicate this beetle from the United States.
“It’s important to look for signs of the beetle now, because it’s slow to spread during the early stages of an infestation,” said Josie Ryan, APHIS’ National Operations Manager for the ALB Eradication Program. “With the public’s help, we can target new areas where it has spread and provide a better chance of quickly containing it.”
The Asian longhorned beetle feeds on a wide variety of popular hardwood trees, including maple, birch, elm, willow, ash and poplar. It has already led to the loss of more than 180,000 trees. Active infestations are being fought in three areas of the country: Worcester County, MA, Long Island, NY (Nassau and Suffolk Counties), and Clermont County, Ohio.
“Homeowners need to know that infested trees do not recover and will eventually die, becoming safety hazards,” warned Ryan. “USDA removes infested trees as soon as possible because they can drop branches and even fall, especially during storms, and this keeps the pest from spreading to nearby healthy trees.”
The Asian longhorned beetle has distinctive markings that are easy to recognize:
- Antennae that are longer than the insect’s body with black and white bands.
- A shiny, jet-black body with white spots, about 1” to 1 ½” long.
- Six legs and feet, possibly bluish-colored.
Signs of infestation include:
- Round exit holes in tree trunks and branches about the size of a dime or smaller.
- Shallow oval or round scars in the bark where the adult beetle chewed an egg site.
- Sawdust-like material called frass, laying on the ground around the tree or in the branches.
- Dead branches or limbs falling from an otherwise healthy-looking tree.
After seeing signs of the beetle:
- Make note of what was found and where. Take a photo, if possible.
- Try to capture the insect, place in a container, and freeze it. This will preserve it for easier identification.
- Report findings by calling 1-866-702-9938 or completing an online form at www.AsianLonghornedBeetle.com.
It is possible to eliminate this pest and USDA has been successfully doing so in several areas. Most recently, the agency declared Stonelick and Batavia Townships in Ohio to be free of the Asian longhorned beetle. We also eradicated the beetle from Illinois, New Jersey, Boston, MA, and parts of New York. The New York City boroughs of Brooklyn and Queens are in the final stages of eradication.
For more information about the Asian longhorned beetle, other ways to keep it from spreading—such as not moving firewood—and eradication program activities, visit www.AsianLonghornedBeetle.com.
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