Purdue Landscape Report: The elm zigzag sawfly (EZS), Aproceros leucopoda, is a non-native insect recently detected in several midwestern states. Originally from eastern Asia, this insect is rarely considered a problem in its native range, having several natural enemies and environmental factors able to keep it in check.
Figure 1. Elm zigzag sawfly adult, Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
However, when in new landscapes, aspects of this insect’s life cycle enhance its ability to spread across new habitats and do significant damage to its host plant, the elm tree. EZS was first detected outside of its native range in Europe in 2003. Then, in 2020, it was found in North America for the first time in Quebec. It has since been detected in several states in the US, spreading first through the Northeast before entering the Midwest. It has not yet been detected in Indiana, but has been in the surrounding area.
Elm zigzag sawfly is a member of the insect order Hymenoptera, which includes bees, ants, and wasps. More specifically, sawflies belong to a suborder known as Symphyta, whose members are noted for a broad-waisted appearance and a saw-shaped ovipositor. Sawflies are a fairly common group of insects, though observers will often overlook them or confuse them for other insects. Adult EZS are generally small, darkly-colored insects that are easy to write off as ‘just another black bug’ you see around the garden or yard (Fig. 1).
Figure 2. Elm zigzag sawfly larva feeding, Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
They resemble wasps, but possess a broad waist with no narrowing of space between the thorax and abdomen, and they lack a stinger. EZS larvae closely resemble caterpillars in both form and feeding habits, with pale green coloration, a black stripe that runs down the length of the body, and dark T-shaped markings on the legs (Fig. 2). The larvae, like moth and butterfly caterpillars, will also possess six pairs of fleshy prolegs that are lost upon reaching maturity. While the larvae bear chewing mouthparts to consume the leaf material of many kinds of plants, the adults are nectar and pollen-feeding. It should be noted that EZS larvae chew zigzag patterns into elm leaves, thus the common name of the insect. Like bees and wasps, sawflies also possess wings, but are typically lazy fliers, choosing to fly only during warm, sunnier periods of the day.
Purdue Agriculture News: As autumn settles in, we eagerly await the transformation of leaves into vibrant hues of red, orange and yellow. However, this year might tell a different story due to prolonged periods of hot weather. Ben McCallister, urban forestry specialist in Purdue University’s Department of Forestry and Natural Resources, sheds light on what to expect this fall.
The Impact of Weather on Fall Foliage Timing
“Right now, we’re seeing a mix of fall coming in and shifting temperatures, which is causing trees to respond. This back-and-forth hot weather is creating some color changes related to drought and stress. This can be expressed as brown color where leaves are starting to wilt and look a little crunchy from exposure to heat and drought stress,” McCallister explains.
While the typical color change occurs from mid-September to early November, it’s not unusual for leaves to remain green at this point in the season. McCallister suggests that while the hot weather “most likely won’t affect anything visually, it could influence fall foliage over time as climate change progresses.”
He anticipates a more pronounced display of fall colors extending through October, with some species showing their colors into November. Ultimately, the vibrancy and timing of these changes will depend on daily temperature fluctuations and the amount of sunlight trees receive.
The environment also plays a significant role in how trees respond. For instance, urban areas with more concrete and buildings create a “urban heat island” effect, which can delay color changes compared to more rural settings.
The Science Behind Color Transformation
The science of fall foliage is both fascinating and complex. McCallister explains that different tree species respond to autumn at varying times, with chlorophyll being a key player in this process.
“Changes in chlorophyll production leads to the color changes in leaves. Chlorophyll allows leaves to take up sunlight and convert it into energy, creating carbohydrates in the form of sugars – really anything that gives energy to the tree to help it grow, sustain itself and compartmentalize,” McCallister notes.
As temperatures cool and the sunlight diminishes, chlorophyll production declines, allowing the green hues of leaves to fade. This decline reveals carotenoids and anthocyanins – two chemicals essential to fall foliage. Carotenoids contribute to the yellow and orange shades, while anthocyanins produce reds and purples. As chlorophyll wanes, these vibrant colors emerge.
“It’s a very cool process,” McCallister adds. “Each color absorbs different spectrums of light, altering energy uptake and preparing trees for leaf drop and dormancy. As leaves in deciduous trees transition, trees store energy in their roots and wood so they can brave the winter.”
Viewing Fall Foliage
When it comes to enjoying fall foliage, McCallister emphasizes that Indiana offers many great viewing locations not far from Purdue’s campus.
Locally, Martell Forest, which is open to the public, is a great spot to check out the fall foliage and immerse yourself in the woods,” says McCallister.
What’s Next?
Leaf drop is likely to occur anytime from mid-October into December, although this process may take longer than usual due to the milder winters we’ve been experiencing. Similar to color changing, the timing of leaf drop varies by tree species and their growth patterns, as well as the overall weather conditions.
“For instance, ginkgo trees turn this brilliant yellow and have a cool reaction to leaf drop. Typically, all their leaves fall within a day or so, creating a carpet of yellow. In contrast, trees like maples and oaks, which have a mix of yellow, orange and red leaves, tend to hold onto their foliage a bit longer,” McCallister recalls.
It’s also important to note that while coniferous trees, like pines, spruces and furs, retain their needles year-round, some conifers like bald-cypress trees drop theirs. This sometimes causes confusion for homeowners who mistake these deciduous conifers for dying trees.
To provide the best care for your trees during these changing weather patterns, McCallister advises familiarizing yourself with different tree species. Resources like Google and dichotomous keys in forestry books can help with species identification and lead to tips for care. Regularly checking your trees’ health is essential year-round. Specialists in your local county Extension offices and ISA Certified Arborists can be valuable resources for proper tree management.
Question: We have a large 60+ foot mulberry tree in our backyard that is located by our pond. This is the first year I have seen these dark streaks on the bark of the tree. Should I have concerns?
Answer: From the photos, it looks like wet wood/slime flux is affecting your tree. It is a bacterial infection on trees and in most cases is not a serious issue, but unfortunately, there is nothing to be done about it. Many years ago they used to drill holes to try and allow gases and liquids drain from an area with the slime flux but through research and experience this practice is not recommended.
The Purdue Landscape Report titled Slime Flux of Trees shares more about this disease:
Slime flux (also known as wet wood) is a dark, foul-smelling and unsightly seepage of sap from tree trunks. The disease is not usually a serious problem but the appearance can be alarming. Slime flux is caused by common surface-inhabiting bacteria or yeast fungi that enter the trunk through wounds associated with improper pruning, stem breakage, injections, cracks from freeze injury or weak limb crotches. The bacteria and yeast may live on sap nutrients within injured trees for many years without any outward evidence.
Symptoms
The main symptom is the appearance of the dark sap oozing on the trunk exterior which happens when gasses produced by growth of the bacteria and yeast cause the internal pressure of the sap to become high enough to force the sap out through cracks in the bark. The dark streaks usually turn light gray or white upon drying. Oozing sap may be frothy and white at the point of exit. Airborne bacteria, yeasts, and fungi often colonize the wet oozing material, which ferments and releases a foul odor. Slime flux may delay wound healing (callus formation).
Lenny Farlee, sustaining hardwood Extension specialist for Purdue’s Department of Forestry and Natural Resources (FNR), has been named a 2024 Fellow of the Society of American Foresters (SAF). The SAF Fellow Award, one of the highest honors bestowed on an SAF member by their peers, recognizes long-standing service to forestry at the local, state, regional and national levels.
Farlee was honored with the award during the 2024 SAF National Convention, which took place in Loveland, Colorado from Sept. 17-20.
Zhao Ma accepts the 2024 Family Forests Education Award on behalf of Lenny Farlee and the other project team members.
“Being named a Fellow of the Society of American Foresters is particularly meaningful to me since it originates from a nomination by my peers at the state level,” Farlee said. “I am very grateful that my colleagues in forestry here in Indiana considered my service worthy of recognition, and I owe much of the credit to them for their support of me through my career. It has been my privilege to serve the people and the profession as an Extension forester here at Purdue.”
Farlee educates people about forestry in many ways, including through the popular Extension YouTube series “ID That Tree,” which has over 100,000 views.
Farlee, Ronald Rathfon, Don Carlson, Jonathan Ferris,Dave Osborne and Phil Woolery worked together to develop the course. The course introduces forest landowners to the biology and management of forests and what resources and professional assistance are available. According to survey results from 2021 participants, “94.4% stated that the information was useful to help them make future decisions and 92.5% stated that the information was useful to help act to manage their property objectives.”
“We in FNR, along with forestry professionals in Indiana and the landowners who have communicated with Lenny and his colleagues through the ‘Forest Management for the Private Woodland Owner’ course, know how valuable this program has been to sustainable forest management in Indiana,” said Zhao Ma, interim department head and professor of forestry and natural resources. “So it is absolutely wonderful when others outside of our FNR community and beyond Indiana also recognize the excellent work that Lenny and his colleagues have been doing…, I would also like to share one more note about Lenny – not only has Lenny been a highly valued and respected member of FNR and the forestry profession for many years, but he is also one of the nicest people I have met. He is knowledgeable yet humble, effective yet gentle, serious about his work yet able to have fun, very busy yet always willing to help others and try to be present. We are lucky to have Lenny as our colleague in FNR.”
Purdue Landscape Report: August was National Check Your Tree Month, but this is something that every tree owner/manager should be doing year-round. As the last hot days of summer are finishing up and we look forward to cooler fall days, we can look to our trees for different signs of trouble.
Most people tend to look up at the canopy before anything else in trees. Check leaves for dieback, discoloration, stickiness or signs of chewing. Check branches and the main stem for damage like splits and breaks, peeling bark, tunneling patterns under the bark, oozing wet spots, or sawdust around the tree. These could be signs of issues in the root system, pathogens like bacteria or fungal organisms, insect problems, or structural damage.
This is not an exhaustive list and if you notice these or anything else that seems off, it could be time for a deeper dive into what might be wrong. If you know the species of your tree the Purdue Plant Doctor is a great tool to narrow down a diagnosis. You can also contact your local Extension office or an ISA Certified Arborist.
On a more positive side, you don’t have to be on the lookout for damage, decline, or signs of pathogens and pests. It is also a matter of enjoying the trees in your landscape. Take some time out of your day to sit in the shade especially as we transition from hot summer temperatures into the cooling of autumn. Revel in the color changes as chlorophyll production slows revealing the carotenoids (that give us yellows, oranges, and browns) and anthocyanin (that produces reds and purples). In winter, not only can you better see damage in the canopy hidden by leaves in the growing seasons, but also the structure and architecture of the canopies in different tree species and the differences in bark textures. And in Spring, new growth of leaves and flowers shows us Winter is nearing its end, bringing warmer days.
So check your trees throughout the year. But not only for potential issues and risk management but also for enjoyment. Trees offer us no many benefits and sometimes it takes a little reminder. If you do see any signs of decline or damage, again, be sure to contact your local Extension office or an ISA Certified Arborist.
Purdue Landscape Report: As summer comes to a close, plants are rapidly releasing seeds and the most noticeable are the flying fluffy type. Thistles, asters and milkweed are just a few of the summer-flowering plants that depend on the wind to disperse their seeds, sometimes carrying them miles away to potentially suitable locations, though seeds typically land within a few meters of the mother plant. This may not be a concern if it’s a desirable plant, but can become extremely problematic when that seed comes from Canada Thistle (Cirsium arvense) (Fig. 1).
Figure 1. Canada thistle (Cirsium arvense), growing amongst common ivy (Hedera helix), produces a fluffy seed that is dispersed by wind.
Canada thistle is found on the list of Indiana Noxious Weeds (IC 15-16-7-2), which mandates that landowners take necessary steps to control and contain the spread of this highly invasive species. Formal enforcement of this Indiana Code falls to Township Trustees, though weed control is a responsibility that is often overlooked. Landowners and homeowners shouldn’t wait for a notice, or knock at the door, from a Township Trustee to begin controlling Canada thistle. It’s listed as a noxious weed for good reason.
Canada thistle is a perennial plant that can reproduce from seed or rhizomes making it difficult to control and contain. Each plant can produce thousands of wind-blown seeds that may remain viable for up to 20 years in the soil. Rhizomes are horizontal underground stems that can grow several feet and put out new shoots (Fig. 2). To add insult to injury, if a rhizome is cut or tilled, a separate plant may grow from each piece of rhizome.
Mechanical and cultural control options for Canada thistle are limited and may reduce plant density, but are not effective at eradicating large, established populations in a landscape. A new population, without an established root system, may be controlled with frequent mowing to deplete food reserves and prevent seed production.Small, isolated populations may be controlled with hand-pulling, but this will need to be repeated every few weeks.
Figure 2. Canada thistle (Cirsium arvense) reproduces by growing horizontal underground stems called rhizomes. Rhizomes can send up new shoots several feet from the mother plant.
Chemical control options include pre- and post-emergent herbicides and, in many cases, applications of both types are needed for complete eradication. A pre-emergent herbicide, with an active ingredient of dichlobenil, is effective at preventing seed from germinating, but will not control established plants. A post-emergent herbicide with the active ingredient of clopyralid is the most effective option for home gardeners. Clopyralid is a selective herbicide for broadleaf weeds, but most vegetable and ornamental plants are susceptible. Precautions should be taken to avoid off-target damage. Read and understand the herbicide label before use. The label is the law.
Regardless of the method used, complete control of an established Canada thistle population will take persistence over multiple seasons. If the fluffy seed is beginning to fly from your thistle patch, it will likely take many more seasons to rid the garden of this pest, but it is possible. To win the battle against Canada thistle, it takes serious grit and an effective herbicide, or a good realtor.
Purdue Landscape Report: Early June, we received a white pine sample at the Purdue University Plant and Pest Diagnostic Lab that showed early season needle loss lower in the tree canopy (Figure 1, 2). The majority of conifers hold onto their needles for multiple years, so loss of needles, even in the fall, can come as a shock to homeowners. In this particular case, we found multiple fungi that could be contributing to needle blight or needlecast.
Figure 1: Eastern white pine trees with early season needle loss.
Figure 2: Closeup images of white pine with needlecast. Multiple fungi were present: Lophodermium, Lecanosticta, and, Septorioides. Note, primarily the older needles have been affected. New needles appear green and healthy.
The first two fungi were determined to be relatively common pathogens for Indiana: Lophodermium and Lecanosticta (brown spot). Symptoms appeared relatively typical for these pathogens where the needles turned brown over-time. However, there were other needles in the canopy and on the sample that had a lighter coloration. We found small black fungal structures dotted along the length of these needles producing light colored cirrhi (also called spore horns) (Figure 3). After examining the fungal spores, isolating the fungus, and performing DNA testing, we determined this third fungus to be Septorioides strobi, the causal agent of Septorioides needle blight of pines. This fungus has been determined to be a contributor to white pine needle damage/defoliation.
Figure 3: Black fungal structures developing on dead needles with white sporulation exuding from the top.
White pine needle damage/defoliation (WPND) was first observed in the state of Maine in 2010 and was attributed to three needle blight diseases, including Lecanosticta, and has since been observed throughout the Northeast US. However, researchers eventually determined that a new fungus, Septorioides strobi, was also found consistently in blighted needles and could be contributing to WPND.
This is the first time we have found this fungus in the state of Indiana, though it has been present for longer than a single season. We do not know how it will react to our climate nor if it will cause significant damage to affected trees. Like other needle blight pathogens, Septorioides has been observed to sporulate around the same time during humid, wet weather, but symptoms may not develop until the following year. White pines are the primary host for this needle cast disease, but it can also develop on 2, 3, and 5 needle pines. While we see white pine decline is a major problem, Septorioides will not likely be the final nail in the coffin for white pines in Indiana, though it certainly will not help us keep them healthy.
MyDNR,Indiana’s Outdoor Newsletter: As a result of Indiana’s positive detection of chronic wasting disease (CWD) in LaGrange County in April, Indiana DNR has restricted moving deer from any CWD Positive Area for rehabilitation purposes.
With the change, an individual who finds an orphaned, sick, or injured deer in a CWD Positive Area may only surrender the deer to a DNR-permitted wild animal rehabilitator that is located within a CWD Positive Area. This restriction is to help minimize the spread of CWD to new parts of the state, as deer can carry this disease without appearing sick.
Currently, there is one CWD Positive Area in Indiana. It includes LaGrange, Steuben, Noble, and DeKalb counties. While no CWD positive deer have been documented in Steuben, Noble, or DeKalb counties, those counties are considered part of the CWD Positive Area because of their proximity to where the state’s first CWD-positive deer was found in LaGrange County.
During their first few weeks of life, fawns often hide by themselves and stay motionless to avoid predators while the mother is looking for food. If you find a fawn alone, you can help it by letting it be, giving it space, and leaving the area. Its mother is likely nearby.
How does forest management affect wildlife, specifically birds? Which birds prefer which types of forest habitat? How can you help birds thrive on your property?
The Forestry for the Birds Virtual Tour is a new tool developed by Purdue Forestry and Natural Resources and Purdue Extension, which offers answers to those questions and more in an easily digestible and visual format. The virtual tour is based on The Nature Conservancy’s Forestry for the Birds program.
The virtual tour is an interactive guide to forest management techniques and birds in the forest that features 360-degree images, including several taken on eight Purdue FNR properties across the state. Bird identification resources from Cornell Lab of Ornithology’s Macaulay Library, forest management resources from Purdue Extension and more make the tour come to life and allow landowners to improve their identification and management skillsets.
Young conducted breeding bird surveys and made recordings of all the species she encountered whether audibly or visually last summer. She utilized a GoPro Max to capture 360-degree images of the properties she surveyed. Song Meter Mini acoustic monitors allowed her to capture various bird songs, which are incorporated into the background of some of the virtual scenes of the tour. Still camera images also provide stunning visuals of each property and bird type.
“I think my favorite thing about the tour is that when you are exploring each scene, it really feels like you are there,” Young explains. “I want folks who may not be able to visit our properties to feel like they are right there, inside the scene, while learning a thing or two about bird conservation and managing our forests for our rapidly declining feathery friends.”
Young is quick to note, however, that it is much easier to spot the birds she added to each scene of the tour than when trying to look for them during surveys, when they are often hiding behind the leaves in the canopy.
Forestry for the Birds is a project developed by the Indiana Chapter of The Nature Conservancy, which provides foresters and private landowners with the information and tools needed to enhance their forests in a way that fosters thriving bird communities. Many resources, including the Forestry for the Birds pocket guides, focus on the “Birders’ Dozen,” or 12 bird species which nest in the Central Hardwood ecoregion of Indiana that are easy to identify by sight and/or sound, and need conservation action to assist with range-wide or local population declines. The Birders’ Dozen species were selected by The Nature Conservancy and an independent group of birders, ornithologists and conservationists.
The virtual tour focuses on how different forest stewardship practices and forest types can benefit a variety of bird species, including the Birders’ Dozen. In each scene, there are three or more bird species to look for, recorded bird songs which are representative of what you could hear in that scene, interactive icons that link to images and videos and an audio description of the scene.
“I’m excited to see this virtual tour come to fruition – it provides some depth of information to complement the Forestry for the Birds Pocket Guide and Silvicultural Guide,” said Jessica Outcalt, Purdue Extension Educator, who helped develop the Forestry for the Birds materials for TNC. “I especially appreciate the visuals and audio that can’t be communicated via printed materials, and how this tour captures the sense of being in a forest that will make the material accessible to a wider audience.”
The properties shown illustrate a variety of forest stewardship techniques ranging from single tree selection to group tree selection, shelterwood, clearcut, oak woodland restoration and prescribed fire. The tour also highlights both young forests and mature closed-canopy forests.
*Bird species listed above with links will take you to the Indiana Woodland Steward website as they share highlights with this information in “The Birders’ Dozen Profile” written by Jessica Outcalt.
The American Woodcock, Wood Thrush and Cerulean Warbler are listed on the National Audubon Society watchlist, while the Cerulean warbler is state endangered in Indiana. The Eastern Whip-poor-will, American Woodcock, Worm-eating Warbler and Hooded Warbler have been noted as species of special concern by the Indiana Department of Natural Resources Division of Fish and Wildlife.
Figure 1: Drought stress can cause decline and, in some cases, death in trees.
Purdue Landscape Report: With recent rain storms across the state, watering may not be at the forefront of everyone’s minds. But as we head deeper into summer it is food to remember most of Indiana is in a state of abnormal dryness to moderate drought, continuing similar conditions from previous years. With that in mind, we should be thinking about the health of our trees (Fig. 1).
Understanding what drought is and its effects on trees can help to bolster care plans. Drought is an extended time with little to no precipitation and can slow growth, reducing photosynthesis, and depleting energy reserves trees need to survive dormancy in winter. Drought conditions can stress trees, making them susceptible to pests and diseases, reducing their ability to produce defensive chemicals, and in severe situations resulting in death (Fig. 2).
One simple task to protect your trees is watering. This is especially important in young and newly transplanted trees. A good industry guideline is the 5-plus-5 rule.
Figure 2a: Wilting in leaves and dieback in parts of the tree can indicate drought stress.
Figure 2b: Wilting in leaves and dieback in parts of the tree can indicate drought stress.
Apply 5 gallons of water plus 5 gallons for every diameter inch of the trunk. For example, a 4-inch tree would require about 25 gallons of water as needed. A good tactic to reduce water runoff from the hose is to take a large bucket and drill enough small holes to create a slow drip watering system. Also check moisture levels in your soil to see if conditions are dry, moist, or saturated.
Another way to maintain soil moisture is to mulch around the tree. Mulch rings should be at least 3 feet in diameter and 2-3 inches deep with a 2–3-inch space between the base of the trunk and the inner mulch ring. Mulching up to the trunk is called volcano mulching and causes issues like stem girdling root production and decay. Mulching reduces evaporation from the soil and helps maintain moderate soil temperatures. It also reduces competition with surrounding lawn and landscaping plants while protecting the trunk from mechanical damage caused by mowing and lawn care practices.
These little steps can go a long way to protect your trees, extending their life spans and your enjoyment with a healthy canopy. For a more detailed look at drought and trees, please have a look at the Purdue extension store here.
