Ironweeds inhabit a broad swath of the United States, from the Mid-Atlantic to the Midwest and from Minnesota south to Texas. While many are tall, even towering in height, all ironweeds offer an abundance of purple-hued flowers in late summer and early fall. Their value as a food source for pollinators is irrefutable — scores of bees, butterflies and numerous other insects feverishly work the flowers throughout the late bloom season. Ironweeds are extraordinary ecological plants, due to their indigenousness and importance as powerhouse pollinator plants, but they are great garden plants, too. At a glance, some ironweeds may seem too tall for many gardens, but recent breeding has resulted in a number of compact hybrid selections. The shorter ironweeds may have given up some size but have lost none of their ornamental appeal or draw for pollinators. Vernonia spp. are in the aster or daisy family (Asteraceae), but lack the showier petal-like ray florets common to the composite inflorescences of coneflowers (Echinacea spp.), asters (Symphyotrichum spp.) and sunflowers (Helianthus spp.). For several weeks beginning in mid- to late summer, purple to magenta capitula bloom in many-flowered inflorescences measuring up to a foot or more across. Leaves are typically dark green and tend toward lance-shaped but can be willow-like to filiform. Conversely, silver ironweed sports bright silvery white linear leaves. Leaf size enhances the robustness of some ironweeds; for example, giant ironweed (V. gigantea) reaches 8 feet tall, but the 10-inch long leaves make it seem even larger. On the other hand, at 3 inches long and barely wider than a sliver, the linear leaves of narrowleaf ironweed (V. lettermannii) look more like Arkansas blue star (Amsonia hubrichtii) than any of its kin.

Most of the commonly cultivated species have woody, fibrous root crowns and stiff stems ranging from several feet to 10 or more feet in height. Ironweeds are generally easy to grow in full sun and moist, well-drained soils but are often adaptable to light shade and drier soils, and some species are drought-tolerant once established. Silver ironweed, for example, is best grown in lean, gravelly soil or decomposed granite, in full or half-day sun. Ironweeds tend to grow taller in moist conditions.

Many ironweeds are hardy to at least USDA Zone 5 or colder, while others are native to warmer places in the Southeast and westward to Texas. Ironweeds are typically long-lived, growing into large clumps over time, but rarely need division. Deadheading reduces unwanted seedlings, which can be prolifically produced, especially in moist areas; however, deadheading removes a food source for late-season songbirds. Powdery mildew and rust can infect foliage in late summer or fall — some species are more susceptible than others. Disease levels can be severe, thus deleteriously affecting plant health. The bitter-tasting leaves are usually not palatable to most grazing mammals including deer. Ironweeds are both a boon and a challenge to gardeners — their size can be daunting for average gardens, but their late-blooming purple flowers attract a host of pollinators. Ironweeds put on an impressive show in native and naturalistic landscapes, meadows and formal gardens.

In early summer, the dark green foliage provides a handsome backdrop for a variety of earlier -blooming perennials; whereas, late-season bloomers such as sunflowers (Helianthus spp.), goldenrods (Solidago spp.), and big bluestems (Andropogon gerardii cultivars) make stellar floral companions. A shorter stature and feathery foliage sets narrowleaf ironweed (V. lettermannii) apart from other species, and provides a pleasing textural contrast with bolder plants. Despite the large number of species — upward of 1,000 herbaceous and woody plants from the Americas, Asia, Africa, and Australia — ironweeds are not widely cultivated and still are uncommon in home gardens.

The evaluation study

The Chicago Botanic Garden (USDA Hardiness Zone 5b, AHS Plant Heat-Zone 5) undertook a comparative trial of Vernonia species and cultivars from 2012 through 2018. The goal of the trial was to determine the garden-worthiness of a variety of cold-hardy ironweeds. The trial group consisted of 17 taxa in all—representing ten species with eight associated subspecies, cultivars, or hybrid selections. Plants were acquired commercially or were grown from wild-collected seeds; seed-grown species exhibited variable traits within a taxon and included V. arkansana, V. baldwinii, V. fasciculata, V. gigantea, V. gigantea ssp. gigantea, V. glauca, V. missurica and V. noveboracensis. The ironweed trial was originally initiated in 2009 but was interrupted in 2010 by a renovation project in the evaluation garden. Due to significant changes in bed design, all plants were transplanted to pots and moved to the production nursery in June 2010. The original 11 taxa were replanted in the trial garden in September 2011; the official restart of the trial began with data collection the following spring. Several new taxa were added to the trial between 2012 and 2015 including V. angustifolia ‘Plum Peachy’, V. gigantea ssp. gigantea ‘Jonesboro Giant’, V. noveboracensis ‘White Lightning’, V. ‘Southern Cross’, V. ‘Summer’s Surrender’ and V. ‘Summer’s Swan Song’.

Five plants of each taxon were grown in side-by-side plots for easy comparison of ornamental traits and landscape performance. The evaluation garden was openly exposed to wind in all directions and potentially received up to 10 hours of full sun daily during the growing season, which averaged 175 days per year for the 2012-2018 trial period. The clay-loam soil had a pH of 7.4 during this period, and although typically well-drained, the site occasionally retained excess moisture for short periods in all seasons. Maintenance practices were kept to a minimum, thereby allowing the plants to thrive or fail under natural conditions. Trial beds were irrigated via overhead sprinklers as needed, mulched with composted leaves once each summer, and regularly weeded. Moreover, plants were not deadheaded, fertilized, winter mulched, or chemically treated for insects or diseases. Plants were cut back to near the base in late winter before new growth began.

In the trial, the ironweeds were regularly observed for their cultural adaptability to the soil and environmental conditions of the full sun evaluation garden; diseases and pests; winter hardiness and survivability; and ornamental qualities associated with foliage, floral display, and plant habits. All taxa were evaluated for a minimum of four years, except for ‘Plum Peachy’, which died during the second winter in two different trials, and ‘White Lightning’, which had been in the garden for only three years when the trial was terminated in autumn 2018.

Top-rated ironweeds

Four ironweeds received five-star excellent ratings, including V. gigantea ssp. gigantea ‘Jonesboro Giant’, V. lettermannii ‘Iron Butterfly’, V. ‘Summer’s Surrender’ and V. ‘Summer’s Swan Song’. These top-rated ironweeds featured superior ornamental traits such as strong vigorous habits, handsome foliage, heavy flower production, winter hardiness, and disease resistance.

‘Jonesboro Giant’ was the largest ironweed in the trial, reaching 144 inches tall and 60 inches wide. ‘Jonesboro Giant’ differed from the subspecies in being significantly taller and narrower in habit, and flowering seven to 10 days earlier. The rigid stems were upright at all times, although the plants relaxed a bit in October during peak bloom. The fine-textured inflorescences and upper stems were dark burgundy. Flower production was consistently heavy, with smallish, ¾-inch-wide purple flower heads; the inflorescences were commonly more than 12 inches wide. The large, dark green leaves were generally healthy, with only minor powdery mildew observed. The late bloom period of ‘Jonesboro Giant’ — late September to early November — was occasionally truncated by early frosts in October; the historical frost date at the Chicago Botanic Garden is October 15. In addition, the large leaves were sometimes tattered by strong winds, especially on the upper half of the stems.

The soft, needle-shaped leaves of ‘Iron Butterfly’ had a similar feathery appearance to another Arkansas native — spring-blooming blue star (Amsonia hubrichtii) — rather than to any of the other ironweeds. ‘Iron Butterfly’ originated in the University of Georgia’s trial garden, and was selected for its vigorous growth, compact habit, and floriferous nature. At 33 inches tall, ‘Iron Butterfly’ was 10 inches shorter than the species and had a tighter habit. Otherwise, the purple flowers were the same color and size as the species, and both taxa were equally floriferous. ‘Iron Butterfly’ was less prone to opening up in the center in heavy rainfall but was not untouched by this issue; damage was always more significant on the species, which was also less likely to rebound than ‘Iron Butterfly’. Powdery mildew and rust were never observed on ‘Iron Butterfly’ or the species. These taxa were the latest of the ironweeds to emerge in the spring. ‘Summer’s Surrender’ is a hybrid cross of V. lettermannii and V. arkansana made by Jim Ault at the Chicago Botanic Garden in 2010. It inherited the bushy habit of V. lettermannii and the larger plant size and capitula of V. arkansana; the olive-green linear leaves — 5 inches long and ½ inch wide — were intermediate between the two species. ‘Summer’s Surrender’ was 48 inches tall and 74 inches wide with a densely broad habit after five years, and it had a passing resemblance to ‘Southern Cross’. From early September to early October, dark purple florets, packed into 1-inch-wide flower heads, were generously produced in airy inflorescences. ‘Summer’s Surrender’ was resistant to powdery mildew and rust.

‘Summer’s Swan Song’ is a hybrid created by Dr. Ault’s crossing of V. lettermannii and V. angustifolia ‘Plum Peachy’. Similar in bushiness and fine texture to ‘Iron Butterfly’, ‘Summer’s Swan Song’ is a slightly larger plant that resists lodging because of its elongated floral branches; the interlocking of the floral branches is a unique trait that helps hold stems upright on rainy days. Deep purple florets in 1-inch -wide heads were plentiful from early September to mid-October. The feathery foliage was moderate to dark olive-green with red petioles, up to 5 inches long and less than a quarter inch wide, and disease-free. After five years in the trial, ‘Summer’s Swan Song’ measured 36 inches tall and 40 inches wide. ‘Summer’s Swan Song’ is hardy in Zone 4, despite the marginal cold-hardiness of ‘Plum Peachy’.

Worthy of more consideration

Ironweeds may be uncommon garden plants but are obvious choices for ecological and naturalistic landscapes, especially for pollinator gardens. The sheer number and variety of insects drawn to their profuse display of late-season purple flowers is astonishing. The only plant group with greater insect visitation in the Chicago Botanic Garden’s trials were mountain mints (Pycnanthemum spp.), and in particular, silvery-leaved P. muticum.

Ironweeds are often overlooked as garden plants due in part to their large size, and perhaps, being native plants, they are not readily available in average garden centers. Furthermore, the dearth of innovation in breeding and selecting new cultivars has until recently exacerbated the matter. Fortunately, the introduction of new compact hybrid cultivars, such as ‘Southern Cross’, ‘Summer’s Surrender’, and ‘Summer’s Swan Song’, has created excitement in the gardening world. Beyond the strong ornamental attributes, easy culture and adaptability to a variety of cultural conditions are merits of ironweeds.

Read the report in full at chicagobotanic.org/sites/default/files/pdf/ plantevaluation/no45_vernonia.pdf.

About the author: Richard G. Hawke is the plant evaluation manager and associate scientist at the Chicago Botanic Garden.

workstation is an area where an employee does a series of repetitive tasks; for example, transplanting, potting, patching or preparing cuttings. The layout of this area can have a large influence on the efficiency of the work that is accomplished.

Basic principles of workstation design and layout have been developed based on time and motion studies, and these have been applied to many industrial operations and tasks. These same principles can be used to improve many of the tasks associated with growing plants and often results in a 20-30% reduction in time.

Design considerations

Include these in any workstation design:

• Worktable
• Incoming materials (prefilled containers, transplants, tags, cuttings to be graded, etc.)
• Location of transplanted container (cart, conveyor)
• Space for the worker
• Container for waste material
• Tools (dibble, pruning knife)

A drawing should be made on graph paper to scale to develop the best layout. It should include the location of the worker, materials and tools.

The following basic principles should be followed:

Workstation height

The best table height is elbow height. Adjustment should be provided for different-sized workers. It is best to provide for both standing and sitting positions as greater efficiency is achieved when workers change positions.

Elbow height should be measured in the standing position. Height adjustment in the chair or stool can bring the worker up to the standing height level. Comfortable chairs with back support and footrests will create less fatigue.

Hand and arm motion

Where possible, both hands should operate as mirror images and both be working at all times. Holding something in one had while the other hand is performing a task is not very productive. If reaching for plants or other things, the distance should be the same for both hands.

Continuous or curved motions are the most natural and productive. Start-and-stop motions require more energy and time. Try to avoid lifting and instead, slide the flats.

The reach from the normal arm rest position should be limited to a 24-inch radius to the side and front for women and a 27-inch for men. Assembly area is best within 16 inches to 18 inches of the resting elbow position.

Workspace

A space of 3 feet by 3 feet is normal for the worker unless a wider work area is needed. Space to the rear should be left for movement of carts.

Adequate lighting over the work area will increase efficiency and reduce eye strain. It should be located above the workstation so as not to create shadows. A level of 40 to 60 foot-candles is necessary. Glare from lights and windows should be avoided.

Location of materials

Locate materials as close to the work area as possible. The farther you have to reach for something, the more time it takes. Walking 10 feet to get, pick up, or set down a flat will add two to three cents to the production cost of the flat.

Tipping the flat toward the transplanter can reduce the distance by as much as 10 inches. Plugs should be dislodged to effect easier removal. Locating a dibble board in a permanent holder so the worker does not have to look to retrieve it.

Prefilled containers from the flat or pot filler are best conveyed to the work area. A belt conveyor with an accumulating station works best. Gravity should be used wherever possible.

A conveyor located to the back of the workstation is best for sending a transplanted container on its way to the greenhouse. The flat or pot is just pushed onto the conveyor. Alternate locations are underneath the workstation bench or behind the worker. This involves moving or turning which takes more time. If carts are used, they should be located as close as possible to each worker.

Inexpensive fixtures or brackets can be installed to hold materials in position while they are being worked on. This frees up one hand that would normally be required for support.

Putting the above principles into practice in your operation can reduce worker fatigue and increase production output.

About the author: John is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to sister publication Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. jbartok@rcn.com

Bark and wood: reunited at last. For decades we have relied on pine bark (or fir bark on the West Coast) substrates to produce most of our container-grown outdoor nursery crops. For a variety of reasons, the use of wood materials as components in bark and peat substrates has increased over the past 15 years. As we discuss more about bark and wood as substrate materials, let’s first discuss some terms associated with different materials regarding substrates. Bark, the outside protective layer of trees, is different structurally and chemically than sapwood (functioning wood closest to the bark) and heartwood (nonfunctioning wood in the center of trees) as illustrated in Figure 1. Bark, a by-product of the forestry industry, has been the backbone of nursery substrates for decades and it remains as the primary material of choice. The inner portion of a tree, the wood, is often referred to even more specifically as “white wood” when describing the brightly colored pieces that can be seen in substrates. Many folks have gone to great efforts to limit the amount of white wood present in bark mixes as a result of growers refusing bark shipments upon delivery or not being pleased when some wood can be seen in bark inventories (Fig. 2A-C). Bark processors/producers across the U.S. work tirelessly to get as much of the white wood as possible out during the processing, aging and handling of the bark substrates, but to remove it all is close to impossible. Some processors have invested in specialized extraction devices to remove strips of inner bark (cambium), limbs, larger chunks of wood or other foreign debris (Fig. 2D) while other processors even have hand-picking stations where larger pieces of white wood are removed.

White wood and fertility

We have been taught to believe that fresh wood, even in small quantities, can cause fertility issues and rapidly decompose in containers leading to poor crop growth. The basis for this caution stems from decades of evidence that when incorporated into mineral/field soils, wood will rob nitrogen from the surrounding soil as it is being decomposed. One big difference in field production and container production with soilless substrates is the amount, type and frequency of fertility that is applied to container crops and the ability growers have to compensate additional nitrogen if/when needed. There is little scientific evidence to suggest that a small percent of white wood in bark substrates will do anything to negatively affect fertility and crop growth. What we have learned over the course of many years of research on bark and wood substrates is that perception is not always reality (maybe rarely so) regarding white wood in bark being bad. Bottom line, the presence of white particles in bark should not be concerning to growers as it relates to substrate fertility, toxicity or decomposition. If anything, the white wood found in bark may have an effect on the physical properties of the overall mix which could present some issues. If, for example, large pieces of white wood are present in bark substrates (Fig. 2C) this could cause water to channel through the container and greatly reduce the container water holding capacity.

In 2013, researchers at North Carolina State University conducted a survey of pine bark substrates from suppliers across North Carolina. A total of 24 products were analyzed for physical, chemical and hydrological properties and of those 12 were identified as the most common products used by nursery growers. After analyzing the physical properties of those 12 samples, the white wood was removed (handpicked with tweezers) and the volume and mass of wood from each sample was determined (Fig. 3A). The physical properties of those 12 wood-free bark samples were analyzed again to determine if any changes had occurred in the physical properties. What we discovered is that the percent (volume) of white wood found in those 12 commercial bark substrates ranged from 22% to 2.5%. We concluded that the main effect seen on physical properties (air and water) was not correlated to the percent wood in the bark but instead it was the size and shape of the wood particles that made the biggest difference in substrate properties. Figure 3B shows the difference in wood particle sizes that were extracted from some of the bark samples. A closer look at six of those bark samples we analyzed can be seen in Figure 4. Sample 1, which had 22% white wood, showed a significant change in air space and water holding when the wood was removed. Sample 3, which had 14% wood, showed very little change in air and water properties when the wood was removed compared to Sample 4, which had half as much wood (7.5%) yet showed significantly higher reduction in air space (-8.0%) and increase in water holding. Bottom line, the presence of white wood in bark only affects air, water, and drainage properties if the size of the wood is very different than the bark.

Bark:wood mixes

All of the white wood discussed so far is wood that is unintentionally added to pine bark substrates. Now, let’s focus on the practice of adding an engineered wood component to bark mixes as a means of stretching bark supplies, lowering costs or other potential benefits. Researchers in Mississippi first tested the idea of growing nursery crops in bark and fresh wood combinations in the early 1980s, but the research never changed industry practice. Fast forward to 2004 and the concept was brought back to life as researchers began an aggressive campaign to investigate the potential of incorporating hammer-milled pine wood in bark and peat-based substrates. Since then, we have a better understanding of how to properly use wood substrates with bark, with peat, or even alone at 100%. There are several commercial wood products on the market produced in a variety of ways. The greenhouse industry has been more aggressive in adopting new mixes that contain wood products due to the significant cost savings when substituting substrate components like perlite. For the nursery industry, aged pine bark remains abundant and cheap so the switch to wood has not been as advantageous. But that has not stopped some growers from wanting to adopt bark:wood mixes nor have researchers stopped investigating how best wood can be used in nursery production now and even more so in the future.

Understanding pH

Recent trials have evaluated bark:wood blends as it relates to crafting specific substrates to have unique air and water properties suitable for large containers or potential for fruit crop production in containers. We have also been working to better understand and predict how the pH of bark and wood blends can be adjusted and maintained. We conducted pH trials in the summer of 2019 at the NCSU Horticultural Substrates Laboratory. Our objective was to evaluate the pre-plant substrate pH modification of aged pine bark when blended with hammer-milled pine tree substrate (PTS) at varying percentages and at increasing rates of dolomitic limestone additions. To produce the PTS, logs of freshly harvested 12-year-old de-limbed loblolly pine (Pinus taeda L.) trees were shredded in a wood shredder before being further processed in a hammer mill. Two commercial wood fiber products, one disc-refined and one extruded material were also evaluated in this trial. All three wood products were blended with aged pine bark at ratios of 20%, 40%, 60%, 80%, and 100% for a total of 15 substrate blends. Each blend was wetted to 60% moisture content and subsamples were amended with 100 mesh dolomitic limestone at rates of 0, 4, 8 and 12 pounds/yard3. Samples were incubated in a controlled climate chamber and sampled for pH determination on 0, 1, 3, 5, 7, 10, 14, 21 and 28 days after lime addition. In this article we will only present and discuss data from the PTS blends (Fig. 5).

The pH of 100% pine bark was the lowest, while the pH of 100% PTS with no lime addition started at 5.8 and increased over the four-week study to 6.2 (Fig. 6). What is not shown are all lime rates in the 100% pine bark. The PTS treatment with 12 pounds of lime had its pH rise to almost 8.0 by the end of the incubated study. Overall, the pH trends were as expected in that the pH increased as the percent PTS increased (and conversely the percent pine bark decreased). The addition of PTS to pine bark even without lime may establish a pre-plant substrate pH range suitable for some crops. The high pH of fresh pine wood can be attributed to several factors including tree species, age of the tree, location of wood within the tree, site location and soil type trees are grown on and season of tree harvest. The pH comes from the acidic nature of the tree components, in particular the organic acids (acetic, formic, oxalic) and polyphenols present in the wood. Over the past 16 years the pH of fresh PTS has been reported to range from 4.4 to 6.0, a range mostly attributed to the season of tree harvest and age of the tree. It should be noted that the PTS used in this trial was fresh. If the PTS was aged, the pH may change and therefore would change the bark mix pH as well once amended. It is also unknown how different bark sources or supplies may alter the initial pH prior to or immediately after potting or the effect of that fertilizer, irrigation water or plants have on pH shift during crop production.

As a side note, the addition of wood products (PTS or commercial materials) has been noted many times to have an effect on rooting and rootball development of numerous woody and herbaceous crop species (Fig. 7). Research trials aimed at studying and quantifying root growth and development in Horhizotrons have shown that as wood percentage increases, so does the speed of root growth of some propagation material (cuttings) and larger plant material being stepped up to larger containers (Fig. 7B). Much is left to learn about this phenomenon but it appears to be linked to the humidity of the substrate environment that wood fiber materials create as well as the physical nature of the thin wood fibers providing ease-of-passage of roots through the substrate to the container wall.

Remember that some percent of unintentional white wood in pine bark substrates does not pose negative production challenges. And the intentional addition of engineered/processed pine wood to bark offers a range of physical properties that could be crafted to certain crops or container sizes. Keep in mind that substrate pH is naturally higher with wood than bark, so if mixes are made using ratios of bark and wood do not assume that “normal or traditional” lime rates are needed or acceptable.

Brian Jackson is an Associate Professor and Director of the Horticultural Substrates Laboratory at NC State University. Brian can be reached at Brian_Jackson@ncsu.edu.

The ever increasing and seemingly unstoppable population of the spotted lanternfly (SLF) (Lycorma delicatula) is significantly embedded in Delaware, Maryland, New York, New Jersey, Pennsylvania and Virginia. While many authorities make an almost continual reference to tree of heaven (Ailanthus altissima) as the preferred food plant for this insect, I would submit an adjustment to the word “preferred.” Field observations in Southeast Pennsylvania shows Ailanthus is common and is a frequent host to the SLF, but the plant is not necessarily plentiful in some areas and population densities can vary from nearly nothing (Bucks County) to extensive (Montgomery, Chester and Delaware counties). However, the spotted lanternfly is quite adaptable in finding new horizons on which to feed. Adaptation has led them to silver maple (Acer saccharinum), which in many quarters is more plentiful than Ailanthus. Oddly, the spotted lanternfly does not rely on other maples and generally leave red maple (Acer rubrum), sugar maple (Acer saccharum) and Japanese maple (Acer palmatum) alone. They do seem to like Acer platanoides, an invasive exotic. SLF has no interest in anything in the Fabaceae family (Cercis, Gleditsia, Gymnocladus and Cladrastis). They have no interest in the Asian flowering cherries nor the Northeast native Prunus serotina. However, the pest does have a strong affinity for things in the Vitaceae family and in lower Southeast Pennsylvania there is a cornucopia of things to go after in that family. It seems almost negligent to discuss Ailanthus and the spotted lanternfly and leave out the members of the grape family. Muscadine grapes (Vitis rotundifolia) reach a northern limit in Virginia but then parade all the way down into central Florida. Vineyard owners tell me that SLF is a major pest in their operations going after wine grapes. American porcelain vine (Ampelopsis cordata), a North American native, is an SLF favorite. But its cousin, the invasive Chinese porcelain vine, (Ampelopsis brevipedunculata) covers extensive areas in the Northeast, Southeast and portions of the Midwest and is the mother lode when it comes to feeding SLF. Casual observation would suggest that porcelain vine is an entrenched, significant component of almost any natural area with varying levels of disturbance. For agricultural authorities to suggest wholesale war on tree of heaven and leave out porcelain vine is woefully insufficient.

Another plant keen on the SLF’s want list is Aralia spinosa, as SLF will flock to the new shoots in the spring while in the instar stage. This native plant occupies a vast area of the Northeast, Southeast and Midwest and is common in the Philadelphia metro area. It is easily spread by seed and is stoloniferous, which forms large colonies, much like tree of heaven. Spotted lanternfly was once dependent on Asian species of plants but has significantly altered its feeding habits to take advantage of some native plants and introduced ornamentals. They like cultivated roses, especially Knock Out Rose, but leave native roses alone, including Rosa virginiana, R.caroliniana and R. nitida. Perhaps this is because those roses have distinct foliar odors that the cultivated roses do not have. SLF instars also have an affinity for the mulberry family (Morus sp). Another clear host is Salix alba ‘Sericea’. It is my observation that aside from porcelain vine, the silver willow is by far the most frequented plant for the instar stage of the SLF. It is not clear if other willows are also on the menu. A rather surprising find is that SLF has preferences for our native black walnuts (Juglans nigra) but not butternut (Juglans cinerea). It is clear however that the insect is adapting fast to what's at hand.

Photos by Bill Barnes

What is abundantly evident is that the SLF instars are looking for plant tissue that is in soft new growth. They prefer new, green, smooth bark and generally have no interest in rough bark or bark that is formidable in any way. They avoid many plants that harbor toxins, except for Styrax japonicus which has considerable amounts of saponins in their tissues. Perhaps this is not by chance. The instars change color from black with white spots to bright red with white spots. As adults they are very colorful with mixtures of red, blue, white, black and gray. Vivid coloration in insects often is a clue to an inherent toxicity. Perhaps what is driving them to certain plants is the acquisition of the plant poisons that they can ingest and incorporate to protect them from predators. This seems more than anecdotal as assassin bugs will readily approach them only to be repelled after reaching a close encounter. Cicada killer wasps have an interest in SLF adults, and they do kill some of them but not on a grand scale. This indicates that potential predators might be limited possibly because they are so vastly outnumbered.

Spotted lanternfly is a hitchhiker with considerable evidence of its egg laying abilities on smooth metal equipment such as the under carriages of trucks, buses, automobiles and, more than likely, railroad equipment. The extent of this is probably greatly underestimated. Amtrak regularly travels from Philadelphia to points west. While waiting for an Amtrak train, one such volunteer traveler flew into my wife's purse as she was headed to Pittsburgh. Had I not spotted it and killed it; this hitchhiker would have easily taken a ride to Pittsburgh. This was in the fall and it could have easily laid eggs and set up shop in Pittsburgh. This capability of the insect to utilize rapid transit of all kinds makes it virtually unstoppable.

The case for control

Are insecticides a possible solution? Maybe for a localized occurrence, but as a practical matter they are largely ineffective — except in agricultural situations. There are too many insects in too many areas not reachable by pesticides, nor is there money available to go after the insect in such a wholesale fashion. There are limits to modeling as a tool considering how widespread the insect is. Areas that are not cultivated nor accessible by any control measures such as egg laying on the underside of roof overhangs, natural areas, hedgerows and state and local parks act as reservoirs for continual repopulation. Killing Ailanthus is a reasonable proposal, but not practical because it will be an almost impossible task and will have almost no effect on the eventual spread of the insect. Killing off Ailanthus for SLF control will only increase the propensity to find new plant species to utilize. If the other plant hosts, such as Ampelopsis, Morus and Salix, are not controlled as well, there is little hope of success in controlling the SLF.

Where is the money to combat this pest and who is going to pay for it? Along the I-476 corridor between the Mid County interchange (I-276) and I-95 are thousands of Ailanthus along a distance of 15 miles through Montgomery, Chester and Delaware counties. Moving south to Delaware and east to New Jersey there are more likely tens of thousands to hundreds of thousands of these trees, along with tens of thousands of acres of porcelain vine which often occur in conjunction to the tree of heaven. The extent of control by any means is a small percentage of what is really out there. Due to propensity for the egg laying on smooth metal surfaces it is impossible to monitor all the railroad cars, trucks, buses, private trailers and other vehicles.

Money spent on non-effective measures should be redirected. The only recourse is to hit this insect with a disease, be it viral or bacterial. Perhaps Bacillus thuringiensisis a possibility. An introduced predator could well cause collateral damage on native insects. Emerald ash borer (Agrilus planipennis) will eventually burn itself out because its food supply of native ash will disappear, and it has not adapted to anything else. But spotted lanternfly does not hesitate to alter its feeding habits and it is here to stay. Germ warfare is the preferred option for control. All the other measures are essentially wasting time and money and will not be effective now or ever.

About the author: Bill Barnes is a horticultural consultant and has been in the nursery business for 45 years. He’s an active member of the International Plant Propagators Society, an IPPS Fellow and received the IPPS Award of Merit. Bill also teaches at the Barnes Arboretum at St. Joseph University in Philadelphia. He introduced Cercidiphyllum japonicum Tidal Wave and Morus alba Green Wave. bill@barnhortservices.com

Opinions expressed are those of the author and do not necessarily represent the views of GIE Media, Inc.