The following articles were compiled during the last 7 days by members of the Extension, Nursery, Landscape, Turf (ENLT) team to benefit those who are managing a commercial nursery, garden center, or landscape business or someone who just wants to keep their yard looking good all summer. Access the BYGL website for additional information on other seasonal topics at: http://bygl.osu.edu
For more pictures and information, click on the article titles. To contact the authors, click on their names.
Poison Hemlock and Wild Parsnip are going to Seed in Southern Ohio (https://bygl.osu.edu/node/1321)
Authors Joe Boggs and Erik Draper
Published on June 21, 2019
Poison hemlock produces white flowers on stalks that create a more rounded look; perhaps a bit more like an umbrella. Wild parsnip has intense yellow flowers with the stalks producing a more flat-topped appearance.
Both are biennial weeds meaning that it takes two years for plants to produce seed. The seeds currently being produced will give rise to plants that spend their first year as low-growing basal rosettes. The plants produce a long, thick taproot while in this stage.
Why Should You Care?
Poison hemlock is one of the deadliest plants in North America. Plants contain highly toxic piperidine alkaloid compounds, including coniine and gamma-coniceine, which cause respiratory failure and death in mammals. The roots are more toxic than the leaves and stems; however, all parts of the plant including the seeds should be considered dangerous.
The toxins must be ingested or enter through the eyes or nasal passages to induce poisoning; they do not cause skin rashes or blistering. Regardless, this plant should not be handled because sap on the skin can be rubbed into the eyes or accidentally ingested while handling food.
Wild parsnip sap contains psoralens which are naturally occurring phytochemicals grouped in a family of organic compounds known as linear furanocoumarins. Psoralens kill epithelial skin cells by inserting themselves into the DNA in the cell’s nucleus. These are the cells responsible for protecting us from long-wave ultraviolet radiation (LWUVR) that bombards us in sunlight.
Severe blistering occurs when skin affected by the psoralens is exposed to LWUVR. The synergistic effect is called phytophotodermatitis (a.k.a. Berloque dermatitis) and the burn-like symptoms, as well as skin discoloration, may last for several months. However, connecting skin blistering to exposure to wild parsnip sap can be a challenge. The cause and effect are muddled by time because symptoms do not appear for around 24 hours after exposure to LWUVR and severe blistering doesn’t peak for another 48 to 72 hours.
Another challenge is that wild parsnip commonly grows in and around poison hemlock. Gardeners exposed to wild parsnip growing among poison hemlock may mistakenly blame the poison hemlock for their ultimate misery.
It is becoming too late to effectively manage either of these weeds in southern Ohio, but there may still be time to reduce infestations in the central or north parts of the states. However, it’s important to remember that once flowers mature, seeds will still be produced on plants that have been cut down.
While it may be too late for control, it’s not too late to suffer from the toxicity of both of these plants. They will remain a risk until collapsing later this season.
Don’t be Fooled
Apiaceae is a large family that includes many innocuous plants. The roots of wild carrot, or Queen Anne’s lace (Daucus carota), are sometimes eaten raw or cooked. Unfortunately, they bear a striking resemblance to poison hemlock roots and misidentifications have been responsible for a number of accidental poisonings.
During this week’s BYGL Zoom Inservice, Erik Draper showed pictures of garden angelica (Angelica archangelica) which is sometimes cultivated for its edible roots and stems as well as its perceived medicinal properties. The stems are a deep purple. As noted above, poison hemlock stems are commonly covered in reddish-purple blotches, but those blotches may occasionally merge to produce an almost solid color.
Crabs, Scab and then So Sad… Drab! (https://bygl.osu.edu/node/1320)
Authors Erik Draper and Joe Boggs
Published on June 20, 2019
On the BYGL conference call, I shared that I am amazed at how the foliage of the greatest landscape small tree, the breathtaking crabapple, has remained relatively clean here in NE Ohio. I was expecting with all of the rain this year, that we would quickly see what we Crabarians affectionately term “year of the scab dog”. This “scab dog” effect is due to the fungal pathogen (Venturia inaequalis) causing extensive apple scab lesions on susceptible crabapple tree leaves. Given our perfect environmental conditions for this fungal disease, I expected it to quickly overwhelm and wreak havoc on crabapples and the genus Malus, which includes eating apples. Infected leaves turn yellow or other fall-type colors, then begin dropping to the ground like rain, resulting in unmistakable tree nudity, thereby rudely creating the “scab dog” tree.
The Natural…and Unnatural History of Trees (https://bygl.osu.edu/index.php/node/1319)
Authors Jim ChatfieldPublished on Junes 20, 2019
Our Tuesday, July 9 program, from 10:00am to 4:00pm will largely be a Walking and Talking program as we explore Secrest Arboretum trees. Trees as you know them (in the 110 acres of the main part of the Arboretum) and the Secrets of Secrest that you may not know – in the part cut off by the highway decades ago. In fact you shall receive a prize if you know the year when this pruning of the Arboretum occurred.
We will explore a cultivated Arboretum and we will also explore forested areas in the older Arboretum section – and we shall see what happens when cultivated plots are abandoned over the years. Which plants invade, Arboretum plants and the run of invasives. We will even see, or at least speculate upon, which plant seeds arrived in the older sections in a hurry following the Secrest Tornado of 2010.
Pest and Disease ID and Management Strategies
Cultural Environmental Problems and Issues
The “Natural” and “Managed” Environments
Natural History Musings
The program is sponsored by Ohio State University Extension, Secrest Arboretum, and The Ohio Independent Arborist Association. The cost is $25. Registration is available at go.osu.edu/chatfield (mThe “c” in chatfield must be lower case for the site to work – I am very modest) and will be $25. You can contact Sarah Mays of OSU Extension at firstname.lastname@example.org or 330-263-3831, fax: 330-263-3667
There will be an assortment of professional horticultural and arboricultural certification credits available.
Other Upcoming OSU Extension Secrest Arboretum Schools to come include:
- Plant Families III: To be rescheduled from July 2.
- “Bugs”: The Good, The Bad, and the Bizarre, August 27.
- “Sustainable Landscaping”, September 3.
- “Ohio Plant Diagnostic Workshop”, September 6.
- “The Sestercentennial of Alexander von Humboldt’s Birth”, September 13-14.
- “Fall Fungal Fest”, October 10.
- “ArborEatUm”, October 22.
- “Fall ArboReadUm”, Date TBA.
- “Why Trees Matter Symposium”, October 31. At the College of Wooster.
“The clearest way into the Universe is through a forest wilderness.” – John Muir.
“The most dangerous worldview is the worldview of those have not viewed the word.” – Alexander von Humboldt.
Authors Erik Draper
Published on June 19, 2019
While on our BYGL conference call, I shared the glorious status of Kousa dogwoods (Cornus kousa var. chinensis) right now in NE Ohio. Only one word can describe them, “OUTSTANDING”!! Then Joe Boggs from the southern reaches of the state, asked me to repeat what I said about the Kousa’s here. I told him that they were just reaching their full glory and were unbelievable due to the cooler weather and moisture.
Joe then laughed and that he just wanted to make sure about what I had said, because their Kousa dogwood blooms were long gone! It is always a good reminder that from one end of the state to the other, the difference in weather conditions and plant material in bloom is often astounding!
So for Joey and all others who blew through the Kousa bloom this year, you can just enjoy them again in pictures, while I enjoy them in person!
Authors Joe Boggs
Published on June 18, 2019
Brood VIII (Eight) of the 17-year periodical cicadas (Magicicada spp.) have made their presence known in parts of northeastern Ohio, western Pennsylvania, and the northern panhandle of West Virginia. As with past brood emergences, the overall geographical distribution is spotty; however, there are localized pockets with heavy cicada activity.
The general impact of a periodical cicada emergence can be divided into two “rounds.” Round 1 starts with the emergence of huge numbers of males and females from the soil where they took 17 years, or 13 years for some broods, to develop. The males then “sing” to attract females for a love tryst. A behavior known as “chorusing” occurs when males synchronize their singing which tests the nerves of besieged homeowners. In short, a full-blown periodical cicada brood emergence is not subtle.
Mated females then use their spade-like ovipositors (ovi = egg, positor = deposit) to create slits and insert eggs into tree stems. This initiates Round 2 which is defined by the short-term and long-term damage caused by periodical cicadas. Although periodical cicadas have piercing-sucking mouthparts just like their aphid cousins, they cause no noticeable damage from their feeding activity.
The physical injury to the vascular and structural tissues of tree stems usually cause the affected stems to break-off and fall to the ground. This may happen immediately with attached leaves remaining green. Or, the stems may remain attached long enough for the leaves to dehydrated, wilt, and turn various shades of brown producing a symptom called “flagging” because it looks like small flags tied to the ends of the branches.
The cicada eggs hatch after a few weeks. The ultimate goal for the newly hatched first instar nymphs is to burrow into the soil to spend the next 17 years (13 yrs. for some broods) imbibing juices from tree roots. It is believed that twig detachment supports greater success and survival of the nymphs on their journey to the soil.
If heavy damage produced by the ovipositing females causes twigs to break-off and fall to the ground, the first instar nymphs just need to step-off into the soil. However, if twigs remain attached, the nymphs must drop from the tree canopy in a leap of faith aiming to land on soil that covers tree roots and not be blown off-course to drop onto a pasture, lake, parking lot, southbound freight train, etc.
The flagging may remain on the trees long after the cicadas are dead and gone. In fact, after Brood V emerged in 2016 which included a large part of eastern Ohio, I received e-mail messages well into August from Ohioans who had traveled I-70 asking why the oaks were looking so bad. It was cicada flagging damage that had never detached.
Cicada oviposition injury that was not severe enough to cause flagging may remain apparent for many years to produce diagnostic challenges. This is demonstrated by the images below.
Of course, the actual tree damage caused by periodical cicadas is considered minimal. It’s long been recognized that although the flagging is very apparent, it causes no real harm to the overall health of established trees. In fact, it could be considered “natural pruning.” Consider that periodical cicadas and their tree hosts have been living together for tens of thousands of years, and yet we still have trees.
Authors Joe Boggs
Published on June 18, 2019
Magnolia scale (Neolecanium cornuparvum) females are “puffing-up” and dripping copious quantities of honeydew in southwest Ohio. This native scale has a strong affinity for non-native magnolias and associated hybrids. Common hosts include star magnolia (Magnolia stellate), lily magnolia (M. liliiflora), and saucer magnolia (Magnolia × soulangeana). Native magnolias are more resistant perhaps because of natural defenses that developed through a shared evolutionary history with the scale.
Magnolia scale is a type of “soft scale” so named because of the helmet-like soft leathery covering that protects the females. Although it’s one of the largest soft scales in Ohio with mature females measuring as much as 1/2″ in diameter, the current pinkish-tan colored females are still somewhat flattened and may be obscured by a heavy coating of white, waxy, flocculent material.
Magnolia scale has one generation per season. Females and males spend the winter as first instar dark-colored nymphs attached to the stems of their host plant. Their resemblance to lenticels makes them inconspicuous. The nymphs mature in the spring with the males developing into small gnat-like insects that fly to females and mate.
The females remain immobile but rapidly expand in size as they mature through the spring and summer. Eggs are produced in late summer to early fall and held internally until they hatch creating the illusion that the females are giving birth to the first instar nymphs (= crawlers). The first instar crawlers are highly mobile but become immobile once they insert their piercing-sucking mouthparts into stems. This is the overwintering stage.
Magnolia scale adults and nymphs insert their piercing-sucking mouthparts into phloem vessels to tap plant sap. A substantial loss of sap from a heavy scale infestation represents a serious loss of energy resources to the trees. The associated physiological stress can produce leaf yellowing and loss, branch dieback and canopy thinning; even the death of entire trees. Stress can also indirectly make trees susceptible to other problems.
Magnolia scale sucks plant sap to withdraw carbohydrates which provide energy and to extract amino acids which are building blocks for proteins. However, the sap contains trace amounts of amino acids compared to huge amounts of dissolved carbohydrates. This means the scale must process a large amount of sap to extract the small amount of amino acids. They discharge the excess sugar-rich liquid from their anus in the form of a sticky, sugar fluid called “honeydew” which is actually a nice name for scale diarrhea.
Magnolia scale is a prolific honeydew producer. During normal years, the sticky honeydew drips onto the leaves and stems of the host plant as well as understory plants to eventually become colonized by black sooty molds. Although the molds do no harm, blackened leaves can seriously reduce the aesthetic appeal of heavily infested trees.
The honeydew also attracts a plethora of freeloading sugar-sippers including bees, wasps, ants, and flies. In fact, a high percentage of the flies are often members of the blowfly family, Calliphoridae. Their maggots may have a taste for decaying flesh, but adults like sweets.
Thus far, this season has not been normal in southwest Ohio. Recurring periods of heavy rainfall appear to be keeping pace with scale honeydew production. Several heavily infested rain-washed magnolias that I inspected recently had little evidence of honeydew on the leaves and no black sooty patina. In fact, given how often I use black sooty molds as a scale (or aphid) indicator, I may have missed the infestation had I not already known the trees were loaded with scale. Of course, the magnolia scale will continue to pump-out honeydew for the better part of the summer, so conditions can quickly change.
Magnolia scale infestations attract a wide range of natural enemies such as the notorious scale and aphid nemesis: the multicolored Asian lady beetle (Harmonia axyridis) with their alligator-like larvae. Sigil lady beetles (Hyperaspis spp.) and Australian mealybug destroyers (Cryptolaemus montrouzieri) may also show-up to chow down on magnolia scales. Both have wool-coated larvae that are actually wolves in sheep’s clothing.
This bio-allies can have a significant impact on maintaining magnolia scale infestations below noticeable levels on native magnolias. Unfortunately, they appear to have a limited effect on magnolia scale populations on non-native magnolias. It’s speculated that the lack of defenses by the non-native trees may support such a rapid scale proliferation, the large numbers simply overwhelm the ability for natural enemies to have a significant effect.
This means other management tactics may be necessary to support plant health. A direct approach is to use physical removal. If trees are small and scale populations are low, a dish scrubber or bathroom scrub brush can be used to physically remove the females before they produce eggs at the end of summer.
Topical insecticide applications targeting 1st crawlers later in the growing season can be effective. However, the extended period of egg hatch presents a serious challenge and requires multiple applications with thorough coverage of the stems. This is particularly true for “horticultural oils” (e.g. summer oils). Thorough coverage is critical because oils only kill on contact. Spring applications can also be effective; however, there is a risk for damaging flower buds.
Control can be achieved with single applications of the neonicotinoid systemic insecticides imidacloprid (e.g. Merit) and dinotefuran (e.g. Safari). There are two effective “treatment windows” in Ohio. They are late summer to early fall, before settled crawlers stop feeding for the season, or sometime in May after overwintered nymphs start feeding. However, spring applications should be delayed until after trees have finished flowering to avoid killing pollinators. Of course, as with all insecticide applications, it is critical to read and follow label directions.