Archives For Pest Alert

What’s black and white and spread all over? Zebra mussels—but they’re no joke.

If you noticed more aquatic “weeds” and algae growing in the Garden Lakes this year—or that our beloved Smith Fountain was MIA after mid-summer—read on to find out why.

Invasive plants and the problems they pose have been the topic of frequent postings here on the Chicago Botanic Garden’s blog. Now we have another invasive species to tell you about—and this time, it’s an animal: zebra mussels.

PHOTO: Adult zebra mussel (Dreissena polymorpha).

Adult zebra mussels (Dreissena polymorpha) are about the size of your thumbnail.

Like many invasive plants and animals, zebra mussels’ native range is a faraway place; in this case, eastern Europe and western Russia. In the past 200 years, they have spread throughout all of Europe and Asia. Here in North America, the first account of an established population was in 1988 in Lake St. Clair (located between Lakes Huron and Erie), likely arriving here as tiny hitchhikers in the ballast water of a single commercial cargo ship traveling from the north shore of the Black Sea.

Somewhat remarkably, over the next two years they had spread throughout the entire Great Lakes. Just a year later in 1991, zebra mussels had escaped the Great Lakes and begun their march across North America’s inland waters. (Watch an animation of their spread). Today they are found in at least 29 states.

A zebra mussel may live up to five years and produce up to one million eggs each year—that’s five million eggs over their lifetime. A freshwater species of mollusk, they prefer to live in lakes and rivers with relatively warm, calcium-rich water (to help support their shell development). They feed by filtering microscopic algae from the surrounding water, with each adult zebra mussel filtering up to one liter of water per day.

Though tiny in size (adults are typically ½ to 2 inches long), their ecological and economic impacts can be enormous. Adult zebra mussels prefer to attach to hard surfaces such as submerged rocks, boat hulls, and pier posts—but they also cling to water intake structures as well as the interior of most any pipe that has flowing water in it (such as drinking water supply and irrigation system piping). From an ecological perspective, zebra mussels’ removal of microscopic algae often causes the afflicted waterway to become much more “clear.” While this clearer water may otherwise seem like a good thing, the now-removed microscopic algae is an important food source for many native aquatic animals. The clearer water also allows sunlight to penetrate deeper into the water, thereby stimulating much more rooted aquatic plant growth.

Nearby, zebra mussels were first identified in 2000 at the Skokie Lagoons, just south of the Garden. In 2013 and again in 2014, just a few zebra mussel shells were found at the Garden on the intake screens for our irrigation system’s South Pumphouse. Since so few mussels were found, we were hoping that the Garden’s lakes were simply not a hospitable place for the zebra mussels to flourish. Unfortunately, that thinking all changed in 2015….

PHOTO: Waterfall Garden label covered in zebra mussels.

These zebra mussels, only a few months old at the time, completely covered this plant label that had inadvertently fallen to the bottom of the Waterfall Garden’s upper pool.

At our Waterfall Garden, 1,000 gallons per minute of lake water are pumped to the top of the garden, after which the water flows down through the garden’s channels and then back into the lake. When Garden staff drained the Waterfall Garden for cleaning in June 2015, there were no apparent zebra mussels present—but by September 2015, the entire bottom of the Waterfall Garden’s upper pool was completely encrusted with attached zebra mussels. Needless to say, we were more than a little alarmed.

Realizing that the Garden’s lakes could indeed support massive growth of zebra mussels, the Garden’s science, horticulture, and maintenance staff quickly came together to devise a remediation strategy that would protect two critical components of the Garden’s infrastructure from “clogging” by zebra mussels: our irrigation system (which utilizes lake water to irrigate nearly all of our outdoor plant collections) and our building cooling systems (three of our public buildings extract lake water to support their air conditioning systems).

PHOTO: One of the Garden's lake water filtration systems.

Automatic backwash filters like the ones pictured here will be added to each of the Garden’s three pumping stations that withdraw lake water to irrigate nearly all of our outdoor plant collections.

The Garden’s zebra mussel remediation team drew upon the best scientific expertise available in North America, which confirmed that there is no scientifically proven approach for removing all zebra mussels from a body of water. The team explored all potential options for eliminating zebra mussel impacts on our infrastructure, and ultimately settled on two approaches: first, the installation of automatic backwash filters to keep even the tiniest of zebra mussels from getting into our irrigation system (the youngest zebra mussels are about 70 microns in size, or about the width of a human hair), and second, the installation of conventional closed-loop “cooling towers” on the three Garden buildings that currently use lake water for air conditioning (thereby discontinuing all withdrawals of the lake water for building cooling). Final design of the backwash filtration systems and the cooling towers is currently underway, and our intent is to have everything installed and operational by spring 2017.

PHOTO: The Garden’s aquatic plant harvester cuts and removes excessive aquatic vegetation and algae from the Garden lakes.

The Garden’s aquatic plant harvester cuts and removes excessive aquatic vegetation and algae from the Garden lakes.

If you visited the Garden in 2016, you probably witnessed some of the zebra mussels’ ecological impacts to our lakes. Mid-summer lake water transparency in our lakes typically is about 3 to 4 feet—but in 2016, this increased dramatically to about 6 feet (likely due to the zebra mussels’ filtering abilities described earlier). This clearer water resulted in much great submerged aquatic plant growth in our lakes, and our aquatic plant harvester struggled to keep up. Many visitors commented that there was much more aquatic “weed” growth in the lakes this year—and they were correct.

In fact, there was so much aquatic plant growth in our lakes this summer that the water intake for Smith Fountain in the North Lake became clogged and the pump burned out. Look for a repaired Smith Fountain (with a more clog-resistant intake) to reappear next spring.

PHOTO: The Smith Fountain (which is illuminated at night) is an acclaimed feature in the North Lake.

The Smith Fountain (which is illuminated at night) is an acclaimed feature in the North Lake.

While there currently is no known way to eliminate zebra mussels from freshwater lakes and streams, Garden researchers intend to utilize the new aquatic research facilities in the emerging Kris Jarantoski Campus to explore experimental approaches, such as biological control agents, to potentially lessen the zebra mussels’ ecological impacts to our 60-acre system of lakes. Stay tuned.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

Last year we discovered Viburnum leaf beetle (VLB) here at the Chicago Botanic Garden for the very first time. As I said then, “I strongly suggest you begin monitoring your viburnums for this critter” as once they move in, they become a perennial pest, just like Japanese beetles.

In early March, we monitored many of the Garden’s viburnums for signs of VLB egg laying and focused on areas where we observed VLB activity last summer. I had read recommendations for pruning out these twigs (with eggs) in the winter as a management technique and wanted to give it a go. To assist with this project, I called in our Plant Health Care Volunteer Monitoring Team; the more eyes the better. The six of us (all armed with hand pruners, sample bags, and motivation) began a close inspection with a focus on last season’s new twig growth for the signs of the distinctive straight line egg-laying sites. In less than five minutes, we found our first infested twig, pruned it out, and put it in a sample bag. After about three hours, we had collected about 20 twigs with eggs.

Truly, I was expecting to find a lot more. This was somewhat disappointing, as I had created a challenge to see which volunteer would fill his or her sample bag and collect the most. This turned out to be more like a needle in a haystack search, as it was a lot more difficult than I had thought. I also feel that the egg-laying sites would have been easier to see if we had done this in early winter, as the egg-laying locations had darkened with time.

Viburnum leaf beetle

Viburnum leaf beetle

Back at our lab, I dissected some of our samples under the microscope. When I removed the cover cap (created by the female after egg laying) material of a few of the egg-laying locations, I found about six orange, gelatinous balls (the overwintering eggs). These eggs were about a month or two from hatching.

For background on this new, exotic insect pest, please see my June 5, 2015, blog on the Viburnum leaf beetle.

American cranberrybush viburnum

American cranberrybush viburnum

  • The favored viburnums are the following:
  • Arrowwood viburnum (V. dentatum)
  • European and American cranberrybush viburnum (V. opulus, formerly V. trilobum)
  • Wayfaringtree viburnum (V. lantana)
  • Sargent viburnum (V. sargentii)
  • When to monitor and for what:
  • In early summer, you would look for the distinctive larva and signs of leaf damage from the larva feeding.
  • In mid- to late summer, you would look for the adult beetle and leaf damage from the beetle feeding.
  • In the winter, you would look for signs of overwintering egg-laying sites on small twigs.
  • Life cycle, quick review:
  • In early May, eggs hatch and larva feed on viburnum leaves.
  • In mid-June, the larva migrate to the ground and pupate in the soil.
  • In early July, the adult beetles emerge and begin to feed on viburnum leaves again, and mate.
  • In late summer, the adult female beetle lays eggs on current season twig growth in a visually distinctive straight line.

viburnum leaf beetle egg laying sites

Hopefully our efforts will lessen the VLB numbers for this coming season. We will see when we monitor the shrubs for leaf damage and larva activity in late May. If nothing else, it was a great learning experience with this very new, exotic insect.

Special thanks to the Plant Health Care Volunteer Monitoring Team: Beth, Fred, Tom (x3), and Chris.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

Emerald Ash Borer has a new host: White fringetree (Update)

Emerald Ash Borer: Sad But True, Part 4

Tom Tiddens —  February 29, 2016 — 2 Comments

Emerald ash borer appears to have spread to a different host, and has now been found and confirmed at the Chicago Botanic Garden. But there’s no need for us to panic—it’s just an interesting find to document. 

As I blogged in late 2014, a college biology professor in Ohio (Don Cipollini, Ph.D., of Wright State University) discovered emerald ash (EAB) borer attacking white fringetrees (Chionanthus virginicus). Soon after his discovery in 2014, the Garden monitored its fringetree collection and found no signs of EAB activity on our fringetree collection (around 40 trees).

PHOTO: Dr. Cipollini holds the limb on which we found emerald ash borer activity.

Dr. Cipollini holds the limb on which we found emerald ash borer activity.

Two weeks ago I had the privilege of meeting Dr. Cipollini here at the Garden and scouting our fringetrees with him. Cipollini and a Ph.D. student are studying EAB on fringetrees and are scouting known populations of fringetrees in areas of EAB activity. Where better than a Garden like ours with a documented collection of fringetrees? 

We scouted nearly all of our fringetree collection very closely. Cipollini knew exactly where to look (way beyond the obvious) and carefully reviewed each of the Garden’s fringetrees. About halfway through the scouting process, a suspicious sunken area was found on one tree. With a sharp chisel, a small section of bark was scraped, revealing a borer gallery. We later removed the limb and found a D-shaped EAB exit hole not far from the gallery. Cipollini indicated that he felt the damage was about 2 years old, and this coincides with time that EAB was at its highest level at the Garden. Of all the trees we very closely monitored, we found only one that had been very slightly damaged by EAB.

PHOTO: The gallery left under the fringetree’s bark by emerald ash borer activity.

The gallery left under the fringetree’s bark by emerald ash borer activity.

We do not need to start treating our fringetrees for EAB or recommend it. The damage is old, and took place when EAB was hitting the Garden the hardest a couple of years ago; so at very high population pressure, it makes sense that they may feed on another closely related tree or shrub. Ash (Fraxinus) is in the olive family (Oleaceae), as is fringetree (Chionanthus), lilac (Syringa), Forsythia, privet (Ligustrum) and swamp privet (Forestiera). These other shrubs are being monitored as well, but it is thought that they may not be an attractive alternative host, as the EAB does not seem to go after small-diameter branches that are prominent on these other olive family shrubs.

As I mentioned in my earlier blog post, I do suggest if you have a fringetree that you look it over for signs of EAB activity.

The Garden is a member of the Sentinel Plant Network, a group that unites botanic gardens in monitoring and providing education on exotic plant pests and pathogens, and works in partnership with the National Plant Diagnostic Network (NPDN).

If you are a plant and bug person like me, please consider becoming a NPDN First Detector and help be on the lookout for these exotic plant pests and pathogens. The NPDN offers an online training course to become a First Detector at firstdetector.org. It’s free, and upon completion, you even get a printable certificate!

©2016 Chicago Botanic Garden and my.chicagobotanic.org

Unwanted wiggler discovered!

About a month ago, one of our horticulturists called me out to look at a groundcover planting that was being heavily disturbed by worms. At first look, I thought nothing of it—maybe it was increased surface worm activity from all the rain. A couple of weeks later, they were still very active, and the groundcover was actually floating on worm castings! We rolled it up to expose many worms. When I picked up a worm, it flipped out of my hand and wriggled away quickly, snake-like—not like a typical worm.

Since this activity seemed strange, I asked our senior ecologist to have a look at the crazy-acting worms. Coincidentally, he identified them as “crazy worms” (Amynthas agrestis), an invasive worm on his watch-for list that has never been found in Illinois. Samples were sent to the University of Illinois for confirmation, and the Illinois Department of Agriculture and Illinois Department of Natural Resources were informed. Our find has been confirmed—along with another find in DuPage County—and a potential find in Wilmette is being investigated. The crazy worm has been in the United States for many years in many of the southeastern states (and in the Smoky Mountains). In 2013, it was found in Wisconsin. DuPage and our find are the first confirmed for Illinois.

PHOTO: Crazy Worm (Amynthas agrestis).

Crazy worm (Amynthas agrestis)

Why is this worm bad?

  • They out-compete and push out our common European earthworms.
  • They multiply very quickly.
  • They devour soil organic matter and drastically change soil structure. This has a huge impact on forest ecosystems as well as on residential and urban ornamental plantings.

How do I identify the crazy worm?

  • They are found near the soil surface.
  • When touched, they respond immediately with a crazy flipping and jumping reaction.
  • They have a fast, snake-like movement.
  • Unlike a common European worm, they have a milky white flat band (clitellum).
  • They are 4 to 8 inches long.
  • A worm may lose its tail when handled.

What should I do if I think I have found the crazy worm?

  • Report the find to the Illinois Department of Natural Resources or Illinois Department of Agriculture.
  • To learn more about the crazy worm, just do a Google search on Amynthas agrestis (crazy worm or jumping worm).

Currently there are no treatments recommended for management of the crazy worm. Education and slowing the spread is the current course of action. The crazy worm’s primary means of spread is through the movement of plants with soil.


The Garden is a member of the Sentinel Plant Network, a group that unites botanic gardens in monitoring and providing education on exotic, invasive plant pests and pathogens, and works in partnership with the National Plant Diagnostic Network (NPDN).

If you are a plant and bug person like me, please consider becoming a NPDN First Detector and help be on the lookout for these exotic, invasive plant pests and pathogens. The NPDN offers an online training course to become a First Detector at firstdetector.org. It’s free, and upon completion, you even get a printable certificate!


©2015 Chicago Botanic Garden and my.chicagobotanic.org

Viburnum leaf beetle is here, and he’s not a good neighbor!

Yesterday was an exciting (yet worrisome) day for me here at the Garden. We found viburnum leaf beetle here for the first time ever—although his arrival was not unexpected. Two separate discoveries were reported to me within just a couple of hours. One of our horticulturists made a discovery in one location, and one of our trained plant healthcare volunteer scouts found the beetle in another location. Both finds were on arrowwood viburnum (Viburnum dentatum), the beetle’s preferred host (and high on our watch list).

Click here to download the viburnum leaf beetle fact sheet with tips on managing the beetle.

If you live in the area, I suggest you monitor your viburnums for our new foreign friend. The sad thing about this critter is that once he moves in, he will become a perennial pest, just like Japanese beetles.

In ornamental horticulture (your home landscape plants), the viburnum leaf beetle seems to be on the verge of having a great impact in our area, as nearly everyone’s home landscape has viburnum. I’d like to take a moment to review this new critter.

Viburnum leaf beetle (Pyrrhalta viburni)

The viburnum leaf beetle (VLB) is native to Europe and was first found in the United States (in Maine) in 1994. It was first found in Illinois (Cook County) in 2009. In 2012 and 2013, the number of reports increased from Cook County and also from DuPage County. In late summer 2014, there were numerous reports from Cook County and some specifically from neighboring Winnetka, where complete defoliation was reported—only five miles from the Garden!

PHOTO: Leaf damage to Viburnum dentatum at the Chicago Botanic Garden by viburnum leaf beetle larvae.

Leaf damage to Viburnum dentatum at the Chicago Botanic Garden by viburnum leaf beetle larvae.

PHOTO: Viburnum leaf beetle (Pyrrhalta viburni) larva.

Viburnum leaf beetle (Pyrrhalta viburni) larva

PHOTO: Viburnum leaf beetle (Pyrrhalta viburni)

Viburnum leaf beetle (Pyrrhalta viburni) by Siga (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons

The VLB larva and adult both feed on foliage and can cause defoliation, and several years of defoliation can kill a viburnum. If you live in the area, I strongly suggest you begin monitoring your viburnums for this critter. There are many great university-created fact sheets for VLB that can be found online, or contact the Garden’s Plant Information Service for additional information. Please report new finds to the Illinois Natural History Survey, Illinois Department of Agriculture, or University of Illinois Extension Service.   

PHOTO: Plugged cavities on a viburnum twig containing egg masses of the viburnum leaf beetle (Pyrrhalta viburni).

Plugged cavities on a viburnum twig containing egg masses of the viburnum leaf beetle (Pyrrhalta viburni). Photograph by Paul Weston, Cornell University, Bugwood.org

Many people ask us: is it true that some viburnums will not be affected by the viburnum leaf beetle?

Viburnum leaf beetles prefer viburnums with little to no hair on the foliage. Plants grown in the shade also exhibit more feeding damage. The University of Illinois Extension has placed viburnums into four feeding categories: highly susceptible, susceptible, moderately susceptible, and most resistant. Viburnum species such as arrowwood (V. dentatum), European and American cranberrybush viburnum (V. opulus, formerly V. trilobum), wayfaringtree viburnum (V. lantana), and Sargent viburnum (V. sargentii) are in the highly susceptible and susceptible categories and can easily be destroyed by repeated infestations of the viburnum leaf beetle. Moderately susceptible species such as burkwood viburnum (V. burkwoodii), blackhaw viburnum (V. prunifolium), and nannyberry viburnum (V. lentago) may exhibit varying amounts of susceptibility, but are usually not killed, depending on the species. Other viburnums, such as Koreanspice viburnum (V. carlesii), Judd viburnum (V. x juddii), and doublefile viburnum (V. plicatum), are resistant to viburnum leaf beetle, will show little or no feeding damage, and are capable of surviving slight infestations. Please contact Plant Information Service at (847) 835-0972 or plantinfo@chicagobotanic.org for susceptibility questions on specific species.

The Garden is a member of the Sentinel Plant Network, a group that unites botanic gardens in monitoring and providing education on exotic plant pests and pathogens, and works in partnership with the National Plant Diagnostic Network (NPDN).

If you are a plant and bug person like me, please consider becoming a NPDN First Detector and help be on the lookout for these exotic invasive plant pests and pathogens. The NPDN offers an online training course to become a First Detector at firstdetector.org. It’s free, and upon completion, you even get a printable certificate!

©2015 Chicago Botanic Garden and my.chicagobotanic.org