Archives For Pest Alert

A gall, tumor, or burl is an abnormal growth on the leaves, stems, roots, buds, twigs, or crown of a plant. In most cases, the gall is unsightly but not damaging. In small plants, the vascular flow of water and food can be restricted, causing poor growth and making the plant more susceptible to other stresses. A large tree can be weakened by an infection over many years. Nematodes, mites, and insects cause 95 percent of galls. Bacteria and fungi cause the remaining five percent. In most cases, the gall-making organism can be identified by observing the structure of the gall and the species of the host plant.

Galls on a Flower

Galls on Rudbeckia laciniata ‘Herbstsonne’

Fungal galls are spread by ascospores in wind and water and can be found on many common trees including oak, maple, and common privet. Black knot affects many species of the genus Prunus—particularly cherries and plums.

Crown gall is a common problem caused by bacteria. The disease is spread by infested soil, transplants, or contaminated tools. The bacteria enters the plant through wounds caused by cultivation, pruning, or insects. Easy prevention methods are to plant only healthy stock (no suspicious bumps), to clean pruners between use on each plant with alcohol or a 10 percent bleach/water solution, and to take care not to injure plant stems. The bacteria stays active in the soil even after removal of infected plants, so place new, healthy stock elsewhere. Remove and destroy all infected plants. Galls caused by bacterial and fungus are more prevalent during wet years.

A gall can form in response to toxins injected during insect feeding or egg laying, or around a feeding larva. The hackberry leaf gall is caused by psyllids, which are tiny winged insects. Galls formed by insects usually do not affect the overall health of the tree unless they experience early defoliation over the course of many years. Parasites are an important control of this pest. Many oak galls are caused by gall flies and generally are not detrimental. A severe twig infection can, however, cause severe injury and even death. Spruce galls are often caused by several species of an aphid-like insect. If only a few galls are present, they can be cut off and destroyed before the insects emerge in midsummer.

Galls on a Flower
Galls on a Flower

 

Leaf galls on maple trees form because of feeding mites. Eriophyid mites produce a gall that resembles a felt patch and may occur on the upper or lower side of the leaf. The overall health of the tree should not be seriously affected.

Nematode feeding activity can injure roots and allow gall-forming bacteria into the plant. Nematodes can also form galls on carrots, camellia, fig, gardenia, okra, potato, roses, sweet potato, and tomato. Plants can be stunted, yellow, and wilted due to restrictions on the uptake of water and nutrients. Individual nematodes are invisible to the naked eye, but egg masses can be seen as pearly objects.  Roots can appear scabby, pimpled, rough, and have knots. Two important prevention methods are to rotate with nematode-resistant crops and to maintain rich organic soil.

Please contact Plant Information Service at (847) 835-0972 or at plantinfo@chicagobotanic.org for additional information.


©2017 Chicago Botanic Garden and my.chicagobotanic.org

Update 4/13/2017: The University of Illinois Extension Program has created a fact sheet for identification of boxwood blight. Download the factsheet here.


Late last year, a colleague asked me to have a look at a boxwood planting at a residence in Winnetka. He indicated that it was looking poor and dropping some leaves. I have seen boxwood with various problems, so I was already guessing what it could be.

Upon arrival, I noted bare sections that had dropped leaves, but also noted strange black streaks on the stems. I ran a moisture chamber test that revealed pink-colored mycelial growth on the leaves, an indication of Volutella blight (a common disease on boxwood that I have seen many times before). More alarmingly, I saw white mycelial growth on the stems that could be signs of boxwood blight—a serious disease of boxwood that has never been found in Illinois. With this in mind, I expressed a sample to the University of Illinois Plant Clinic for diagnosis. About two weeks later, I received a call from the Illinois Department of Agriculture (IDOA) regarding the sample, and yes…it was positive for boxwood blight.

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Since then, boxwood blight has been found in two other locations in Illinois. All have been traced to nursery stock that came from a source that was not in Illinois; this is good. The IDOA is hopeful that these are isolated incidents that can be contained. Later this month, the IDOA will likely issue a “nuisance declaration” for boxwood blight; this will allow them the authority to mandate proper removal of infected boxwood in an effort to stop any spread.

Boxwood blight photo by David L. Clement, University of Maryland, bugwood.org

Boxwood blight photo by David L. Clement, University of Maryland, Bugwood.org

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Boxwood blight was first discovered in the United States in 2011. Currently, it has been identified in 18 states, primarily in the east. It is being managed at a state level, with various states having different regulations. Some states require nurseries to practice boxwood blight cleanliness programs to ensure the plants they sell are disease free. Here at the Chicago Botanic Garden, we are developing protocol to monitor incoming plants and to monitor our existing collection.

Now that boxwood blight has been found in Illinois, and because boxwood is such a common landscape planting, I feel we should all have a good understanding of this new pathogen. There is no need to panic, but if you have boxwoods, you should monitor them this growing season. I will briefly review boxwood blight for you, but you can find many great fact sheets online by searching for “boxwood blight.” One fact sheet that I found very comprehensive was titled, “Best Management Practices for Boxwood Blight,” from the Virginia Cooperative Extension. Also, the Garden’s Plant Information Service can help you with questions about boxwood blight, but we ask that you do not bring in samples. Call (847) 835-0972, or email plantinfo@chicagobotanic.org.

Photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Boxwood blight (Calonectria pseudonaviculata) is a serious fungal disease that primarily affects boxwood (Buxus spp.), but can also hit Japanese pachysandra (Pachysandra terminalis), and sweetbox (Sarcococca spp.). Boxwood blight causes leaf spots, stem cankers, and defoliation. The pathogen itself does not kill the plant, but weakens it to a poor state of health, allowing secondary pathogens to kill the plant. The primary means of spread is by movement of contaminated plants, but it can also be spread via pruning tools, clothing, equipment, and contaminated soil/organic matter. The pathogen can survive in soil and organic matter for years and is easily disseminated by water movement.

Management suggestions:

  • Monitor your boxwood (at least one a month). Look for the following:
    • Leaf spots—light or dark brown circular lesions, often with a yellow halo.
    • Stem cankers—dark brown to black cankers on the stem, diamond shaped or as vertical streaks.
    • Defoliation—sections of the plant dropping leaves.
    • If you feel you have found boxwood blight, you should contact the IDA or send a sample to the University of Illinois Plant Clinic for diagnosis. Please do not bring suspect samples to the Garden.
  • Inspect purchased plants carefully before bringing them home.
  • Home care:
    • Plant in locations with good air circulation.
    • Prune to increase air circulation.
    • Sanitize pruning equipment before going from one plant to another. Lysol disinfectant works well.
    • Water at a time of day that the plants will dry quickly.
    • Avoid overhead watering if possible.
    • If desired for a hedge or mass planting, it is best to plant loosely and allow them to grow into each other; do not plant tightly.

If we learn of anything new with boxwood blight in Illinois, we will do a follow-up blog. For now don’t panic; just monitor, monitor, monitor.


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!


©2017 Chicago Botanic Garden and my.chicagobotanic.org

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