BYGL Weekly News for June 5, 2023
The following articles were compiled during the last 7 days by members of the Buckeye Environmental Horticulture 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
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Authors Amy Stone
Published on June 5, 2023
Tyler Carr, Ph.D., Turfgrass Extension Specialist and Assistant Professor, recently shared some important information about turfgrass and drought stress. The information includes what you can do, and what’s ahead.
Check out this informative post: https://buckeyeturf.osu.edu/news/drought-stress-underway
Drought Stress Underway
Authors Joe Boggs
Published on June 3, 2023
2023 is shaping up to be “The Year of the Aphid.” At least, in southwest Ohio. I’ve already posted BYGL Alerts on aphids titled, Sticky, Dripping European Beech, and Sticky, Dripping Oaks. This Alert will be the third in the “Sticky, Dripping” series.
I visited tuliptrees (Liriodendron tulipifera (family Magnoliaceae)) earlier this week in a municipal park in southwest Ohio with leaves so sticky they were like fly paper. The trees had one of the highest populations that I’ve ever seen of our native Tuliptree Aphid (Illinoia liriodendri).
Why are there so many aphids this season? First, most species of aphids found on deciduous trees are “cool-season” insects. For several reasons, they do best in the spring and fall. We certainly had a long, cool spring.
Second, heavy, driving rains are the enemy of aphids. They get washed off and have a hard time climbing back up their woody Mt. Everest. Heavy rains may also wash away honeydew deposits. While we had relatively abundant rainfall this spring, we did not have many storms that packed high winds to produce driving rain.
Third, aphids have a very high “reproductive potential” meaning that aphids are very good at making more aphids. For example, tuliptree aphids that develop in the spring are parthenogenetic meaning the females don’t need to be fertilized by males. Also, the females give birth to live young. So, they don’t need to take time to mate, and no time is lost with eggs hatching.
Finally, a long, cool spring also slows the development of the “3-Ps”: Predators, Parasitoids, and Pathogens. These natural regulators help keep aphids in check. Of course, this is changing rapidly. It was easy to find predators on the hunt for the tuliptree aphids.
The handiwork of small wasps in the genus Aphidius (family Braconidae) was also on display. The wasps use their tiny ovipositors (ovi = egg) to insert a single egg inside aphids. The wasp larva consumes the aphid’s innards leaving behind a puffy, dry, husk referred to as an “aphid mummy.” A hole in the mummy indicates a new wasp has emerged. There were only a few mummies; however, this could soon change.
Other Sources of Sticky, Dripping Liquid on Tuliptrees
Our native Tuliptree Scale (Toumeyella liriodendri), which is a type of “soft scale”, may also appear on tuliptrees as well as magnolias. It’s a reminder that tuliptrees and magnolias are family relatives. There’s also the possibility that tuliptrees are infested with Calico Scale (Eulecanium cerasorum). This non-native soft scale has a broad host range including tuliptrees.
Aphids and soft scales feed the same way. They insert their piercing-sucking mouthparts into phloem vessels to tap plant sap. They withdraw carbohydrates which provide energy and extract amino acids which are building blocks for proteins. However, the sap only contains trace amounts of amino acids compared to huge amounts of dissolved carbohydrates.
This means they 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 or aphid diarrhea.
The honeydew drips onto the leaves and stems of the host plant as well as understory plants. It commonly attracts a plethora of freeloading sugar-sippers including bees, wasps, flies, and ants.
The honeydew on leaves and stems may eventually become colonized by black sooty molds. Although the molds do not harm plants; they’re not pathogenic, heavy leaf coverage on small plants could interfere with photosynthesis. The blackened leaves also reduce the aesthetic appeal of heavily infested trees.
Tuliptree scale produces periodical outbreaks in Ohio with the last one occurring in 2012. However, this scale has been an annual no-show ever since. This does not appear to be an outbreak year unless readers report that they’re seeing high populations.
Although tuliptrees in southwest Ohio have finished blooming, it’s important to keep in mind in the spring that the flowers may be another source of sticky, dripping liquid. The flowers are a well-known bountiful source of nectar for honeybees and other pollinators. However, the primitive flowers do not yield their sugary bribe to pollinators in the same way as more advanced flowers.
The nectar simply pools in the base of the cup-like flowers. It’s not unusual for the nectar to seep between the 6 upturned petals to drip onto the 3 downward-hanging sepals that act like a nectar sluice directing it onto leaves and branches. The clear, sweet, sticky liquid is a dead ringer for honeydew. A word of caution based on personal experience. Tipping over the flowers may release a voluminous flow of nectar to ruin your day.
An Unusual Observation: Crystallized Honeydew
On a final note, while taking pictures in the park of tuliptree aphids, I came across burr oaks with heavy deposits of honeydew on the leaves from Myzocallis oak aphids. These aphids don’t infest tuliptrees and tuliptree aphids don’t infest oaks.
Our rainfall has all but ceased in southwest Ohio, and temperatures are more August-like than June-like. The environmental conditions have caused the honeydew to crystallize as shown in the images below. The pattern reminded me of salt crystals that form at the edge of evaporation ponds. The crystallization may have hampered the colonization of the honeydew by black sooty molds.
This honeydew crystallization is something I’ve never observed with aphids or soft scales. However, I did observe it last season with spotted lanternfly (Lycorma delicatula) in Cincinnati during a late-season “mini-drought.”
Authors Joe Boggs
Published on June 1, 2023
Overwintered Bagworm (Thyridopteryx ephemeraeformis) eggs are hatching in southwest Ohio meaning the “bagworm season” is now underway. Look closely at trees and shrubs festooned with last season’s bag abodes.
Bagworms are moth larvae (caterpillars) that develop within silk bags festooned with pieces of their host plants. They never leave their bags throughout the 7 stages (instars) of their larval development. The caterpillars attach their bags to their plant hosts with a small stand of silk and extend their bodies a short distance out of the bag to feed.
Bagworm populations were on a rising trajectory from year to year in Ohio throughout the late 2010s peaking in 2020. However, the caterpillars were almost a no-show in 2021 as well as last year.
Of course, there continued to be isolated pockets with damaging populations throughout Ohio in 2021 and 2022, but widespread populations were confined to the northern part of the state. Thomas Dehaas (OSU Extension, Erie County (Sandusky)) reported on several occasions that bagworms were a continual problem in the counties bordering Lake Erie.
However, bagworms have a history of “now you see me, now you don’t, now you see brown shrubs!” Thus, successful management to avoid plant damage must focus on early detection regardless of what happened last season.
Bagworm Behavior and Detection
It is a common misconception that bagworms only eat evergreens. Indeed, they are frequently called “evergreen bagworms” in many southern states although “bagworm” is the Entomological Society of America’s approved common name for the species. However, the caterpillars may be found feeding on over 125 species of evergreen and deciduous woody plants in 45 plant families.
It’s important to pay close attention to deciduous trees and shrubs as well as evergreens. Overlooking deciduous trees and shrubs during bagworm inspections allow infested plants to become reservoirs for infestations to spread to neighboring host plants, sometimes from deciduous hosts to evergreens.
The 1st instar caterpillars of this native moth are very small with their bags measuring around 1/8″ in length. 1st instar bags are constructed with pieces of tan to reddish-brown sawdust-like frass (excrement) stuck to the outside of silk and look like “dunce caps.”
As the bagworm caterpillars mature, they begin weaving more and more host plant debris into the silk which provides structural stability as well as camouflage. This behavior makes bagworms one of the sneakiest general defoliators found in Ohio landscapes. Heavy infestations are commonly overlooked until the caterpillars have produced substantial feeding injury.
The overwintered eggs hatch within the female bags from last season. A percentage of the 1st instar caterpillars will crawl from the old bags and produce a strand of silk to catch the wind and “balloon” the tiny caterpillars to new locations. This behavior is one of the reasons bagworms often appear on hosts that were not infested last season. However, heavy rain and high winds quickly destroy the delicate silk strands.
Although bagworm caterpillars may waft in on the wind to establish new bagworm beachheads, looking closely at trees and shrubs with last season’s bags is a good way to detect this season’s crop of bagworms. A single female can produce 500 – 1000 eggs meaning that populations can climb rapidly. Just a few “founding” females from last season can spawn damaging numbers of caterpillars this season.
The “founder effect” with bagworms often translates into hotspots. These can be seen both within infested plants as well as between infested plants.
Stopping bagworms from producing noticeable damage may include both passive and active approaches to management. A passive approach is to design landscapes that have a diverse range of flowering plants. But more on that later.
An active approach is to closely inspect susceptible trees and shrubs and apply properly timed insecticides. However, this approach can be problematic.
There’s a general rule with using insecticides that the bigger they are, the harder they are to kill. This is certainly true with bagworms. The smaller early-instar caterpillars are easier to kill compared to the larger later-instar caterpillars.
However, bagworm eggs may hatch over an extended period and eggs on the south side of an infested plant usually hatch earlier than those that are shaded on the north side. This creates asynchronous development with bagworms meaning it’s common for a wide range of instars to be present at the same time. This is illustrated in the image below and must be taken into account in planning management strategies.
For example, early instar bagworms are highly susceptible to the naturally occurring biological insecticide Bacillus thuringiensis var. kurstaki (Btk) (e.g., Dipel, Thuricide, etc.). Caterpillars are much less susceptible once bags surpass 2/3″ in length. It’s appealing to use Btk products because they do not kill bio-allies such as predators and parasitoids that help provide natural control of bagworm populations.
However, Btk products have two limitations. The active ingredient must be consumed to kill caterpillars and the products have relatively short residual activity. Thus, timing is critical; products should not be applied before the eggs hatch. Even with proper timing, two or more applications may be required to cover the extended egg hatch. Of course, once bags exceed 2/3″ in length, standard insecticides will need to be used to suppress heavy infestations.
Bagworms may also be managed with topical insecticides. However, those selected should have a minimal impact on the natural enemies of bagworms. There are at least 11 species of parasitoid wasps that have been found to attack bagworms. Baldfaced hornets (Dolichovespula maculata) are also a known nemesis of bagworms. Thus, so-called “bio-rational” insecticides are a good choice.
Biological Control by Connecting-the-Dots: It’s well documented that a wide range of enemies of insect pests are fueled by nectar. They are pollinators as well as predators or parasitoids. Thus, an effective long-term insecticide-free bagworm pest management strategy is to simply plant flowering plants that provide nectar.
Common bagworms are commonly targeted by an array of predators, parasitoids, and pathogens (the 3-Ps). I’ve observed bagworm bags ripped open by baldfaced hornets to extract the caterpillar meat morsels inside. I’ve also commonly observed these wasps visiting flowers. They are pollinators and predators.
A scientific paper published in 1976 showed that the parasitoid wasp, Itoplectis conquisitor (family Ichneumonidae) accounted for almost 76% of the parasitism observed on common bagworms in the study. This parasitoid wasp commonly visits flowers to sip nectar. It’s a pollinator and a parasitoid.
A study published in 2005 showed parasitism rates of I. conquisitor exceeded 70% in bagworm-infested plants that were next to a central flower bed, but less than 40% in infested plants with flower beds further away. In other words, if you plant them, they will come.
Selected Scientific Literature
Davis, D.R., 1964. Bagworm moths of the western hemisphere (Lepidoptera: Psychidae). Bulletin of the United States National Museum.
Sheppard, R.F. and Stairs, G.R., 1976. Factor Affecting the Survival of Larval and Pupal Stages of the Bagworm, Thyridopteryx Ephemeraeformis (Lepidoptera: Psychidae). The Canadian Entomologist, 108(5), pp.469-473.
Ellis, J.A., Walter, A.D., Tooker, J.F., Ginzel, M.D., Reagel, P.F., Lacey, E.S., Bennett, A.B., Grossman, E.M. and Hanks, L.M., 2005. Conservation biological control in urban landscapes: manipulating parasitoids of bagworm (Lepidoptera: Psychidae) with flowering forbs. Biological Control, 34(1), pp.99-107.
Moore, R.G. and Hanks, L.M., 2004. Aerial dispersal and host plant selection by neonate Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae). Ecological Entomology, 29(3), pp.327-335.
Rhainds, M., Régniere, J., Lynch, H.J. and Fagan, W.F., 2013. Overwintering survival of bagworms, Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae): influence of temperature and egg cluster weight. The Canadian Entomologist, 145(1), pp.77-81.
Authors Amy Stone
Published on May 30, 2023
Check out the most recent video or podcast of the OSU’s Tuurfgrass Team Times in preperation of higher temperatures and drier conditions.
Experts contributing to this week’s resource include Pamela Sherratt; Dr. Dominic Petrella; Tyler Van Landingham; Dr. David Gardner; Dr. Tyler Carr; and Dr. Ed Nangle.
Topics include water managment and leaf appearance in cross-section over the growing season; turfgrass research plots across Ohio; weed management; wetting agents; and the no mow may trial continues.
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