emerald ash borer – My Chicago Botanic Garden

Viburnum Leaf Beetle Update – Winter Scouting

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.

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.

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.

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.

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

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!

Pest Alert: Viburnum Leaf Beetle

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) — 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!

Emerald Ash Borer: Sad But True, Part 3

Last week, a college biology professor in Ohio announced he had found evidence that the emerald ash borer (EAB), an invasive insect decimating the continent’s ash trees, is also attacking white fringetrees (Chionanthus virginicus).

PHOTO: White fringetree in bloom. — White fringetree (*Chionanthus virginicus*) in bloom

In August he found the telltale D-shaped exit holes on a fringetree near his home. When he investigated further by peeling back the bark, he found feeding galleries and live borers. He had the borers positively identified morphologically as well as with DNA tests conducted by the USDA’s Animal and Plant Health Inspection Service (APHIS). He also found evidence of EAB activity on fringetrees in three other locations in Ohio.

The recent discovery marks the first time EAB has been found completing its life cycle on anything other than ash in the United States.

The finding adds an alarming new element to the EAB story:

Researchers have been wondering whether the host range for EAB could be wider than just ash. That theory had seemed unlikely up to now but is proven with the fringetree discovery. There has already been a lot of research investigating other possible hosts, and with the new discovery, there will likely to be more.
Is the insect adapting? This is a scary thought!
Will EAB kill fringetrees as it does ash, or just cause damage? So far the invasive insect appears to only be damaging—not killing—fringetrees.
Has EAB moved to fringetrees because EAB populations are locally so high? If the buffet is crowded at the “prime rib station,” it seems logical that “meatloaf station” may get some visits.
What will happen when ash tree populations dwindle? Will the EAB population die back, or just move to a secondary host (the meatloaf, as the prime rib is gone) and/or develop a completely new palate?

PHOTO: A D-shaped exit hole left by EAB. — This D-shaped exit hole was left by a mature emerald ash borer as it exited this host tree.

The Ohio professor’s find was not all by luck; he had reason to focus on the white fringetree. Laboratory studies have shown that the adult EAB will feed on the foliage of other tree species in the same family as ash—the olive family, or Oleaceae. Members include ash (Fraxinus), fringe tree (Chionanthus), lilac (Syringa), forsythia, privet (Ligustrum) and swamp privet (Forestiera). Literature from Asia, the homeland of the EAB, indicates other secondary EAB hosts.

The Chicago Botanic Garden has 42 fringetrees; all have been inspected and show no signs of EAB activity. Even a fringetree that is 25 feet from an ash tree that was heavily infested with EAB shows no signs. If you have a fringetree, you should inspect it for signs of EAB. These include dieback starting at the upper limbs of the tree, new growth on the lower trunk, and small, D-shaped holes where the larvae have exited through the bark. Emerald ash borer larvae can kill a mature ash tree in two to three years by destroying the tree’s vascular system.

Find more information on identifying and dealing with EAB on our website, and in our previous posts, Signs of Emerald Ash Borer, and Emerald Ash Borer: Sad But True, Part 2.

As the world has become less fragmented by ease of transportation, more exotic, high-consequence plant pests and pathogens like EAB have entered—and will continue to enter—the country. Other exotic plant pests and pathogens we are watching for at the Garden include the following: viburnum leaf beetle, Lymantria dispar asiatica moth, brown marmorated stink bug, Asian longhorned beetle, thousand cankers disease, plum pox virus, chrysanthemum white rust, sudden oak death, and so on; most are already in the country. Vigilance and education are the key to managing and slowing the spread of these foreign invaders.

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!

Emerald Ash Borer: Sad But True, Part 2

In the past few months, the number one question I have been asked is “Will the cold winter have an effect on the emerald ash borer?” It’s sad but true that our cold winter will have very little effect on the emerald ash borer.

PHOTO: Emerald ash borer larva closeup. — An emerald ash borer larva lurks just under the bark of one of the Garden’s ash trees.

As we know, the emerald ash borer overwinters as larva under the bark, and that alone gives it some winter protection. More importantly, the emerald ash borer has another very interesting overwintering strategy: “supercooling.” In the fall, as the borer senses the cooler temperatures, it begins to produce a natural antifreeze that allows it to survive well below 32 degrees without freezing. The borer can also purge its stomach of materials that could freeze, flattening out and folding over. They are often found in this folded-in position under the bark in spring—I have seen this firsthand when I scraped the bark off an ash in January. Researchers in Minnesota have determined that it takes a prolonged period of about minus 25 degrees Fahrenheit or more to kill the borer. Our lows this past winter only reached about minus 16 degrees Fahrenheit (twice), as recorded by the Chicago Botanic Garden’s weather station. So, in our area, the march of the emerald ash borer continues undisturbed by our nasty winter.

PHOTO: A neighborhood ash tree with huge gaps in foliage, caused by dieoff from borer damage. — Crown die-off, due to emerald ash borer damage. Photo by Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org

If you have ash on your property, I recommend monitoring closely for signs of emerald ash borer; if you don’t see signs, it is only a matter of time. When you do discover the borer, begin treatments as soon as possible. Treatments are best made proactively—before you see signs of damage on the tree! You may wish to simply plan/budget to have your trees removed. Be aware that dead ash trees are hazardous, not just for their spread of the beetle. They become brittle quickly and become a hazard as limbs fail and fall.

The Garden is a great resource if you have questions or just want to learn more about the emerald ash borer. If you have recently removed ash trees, or have already scheduled removal and are looking for replacement trees, consider our list of ash tree alternatives. Drop by our Plant Information Service with your questions! Our new location is outside the Lenhardt Library.

Click here to register online for one of two informational sessions, Emerald Ash Borer: What You Need to Know, from 10 a.m. to noon on Friday, May 16, and Saturday, May 17. This is a free seminar, but advance registration is required.