Seeking a “Vaccine” for Spotted Lanternfly

The author applies systemic insecticide to kill ailanthus trees. All photos courtesy of the author.

In a year overshadowed by a pandemic, I wasn’t sure how the tree care industry was going to fare. I was preparing to start my spring horticultural-oil treatments when the world basically stopped. During the first couple of weeks, it seemed as if no one really knew what we were or were not allowed to do. Timing is very crucial in plant health care, so any delays in pesticide application could greatly affect your integrated-pest-management schedule.

It was a frustrating time, not only with the unknowns of what was going to happen with the pandemic, but also knowing that tree diseases and insects do not abide by the same restrictions we humans were now facing. Slowly but surely, life started to resume again in central Pennsylvania. As landscaping companies started to trickle into their springtime routine, it appeared as though the green industry was getting the green light.

Nymphs converge on a single stem of an ailanthus tree in Mifflin County, Pennsylvania.

Tree diseases and insects do not care about our schedules; they do not quarantine themselves while we all try to make sense of things. I was really curious to see how people were now going to respond to their tree issues, especially the spotted lanternfly (SLF). Over the last few years, I’ve observed whole communities become affected by the invasive insect; would it now take a back seat while COVID-19 took priority? It was a real concern; backing off, even a little, could represent huge gains for the SLF geographically.

When I first became involved with SLF in 2018, I had to travel at least two hours to find any known populations. I felt it was only a matter of time until it hit home here in central Pennsylvania, and I wanted to become as knowledgeable about it as I could. I only had a handful of SLF customers, but I learned a lot that year. I was used to doing mostly foliar applications of insecticide on small ornamental trees, but learned very quickly that customers want systemic treatments that will continue to work for several weeks. A single foliar spray may kill lots of SLF, but it does not keep new ones from coming back and feeding on the same tree, possibly within days.

Note how the SLF open their wings when feeding on a tree that has been treated with a systemic insecticide.

The spotted lanternfly’s tree of choice is the tree of heaven, or ailanthus. This is an invasive tree that thrives in disturbed areas such as roadsides and railroad rights of way, so, naturally, the insect is going to follow these routes, not only traveling from tree to tree but also “hitchhiking” on vehicles or any objects that get transported. The very next year, I was conducting treatments in the Harrisburg area along the railroad lines. In only one years’ time, I went from having to drive two hours to see an SLF to only one hour! I can’t say I was surprised to see such a geographical jump, since the railway provides not only transportation but a plethora of ailanthus trees for them to feed on as well.

One of the reasons I can keep track of the movement of SLF is because I also work as a contractor for the Pennsylvania Department of Agriculture (PDA), for their spotted lanternfly program. PDA has been working on monitoring and battling the SLF since it was discovered. I was curious to see if there was still an SLF program this year or if COVID was going to interfere. Fortunately, I was eventually contacted by PDA and able to conduct work for them this year. Both the U.S. Department of Agriculture and the PDA conduct work that helps to slow the spread of the spotted lanternfly by eliminating ailanthus on certain properties and by creating “trap trees” with the use of systemic insecticides. For more information about what each department is doing, I suggest visiting their websites. (See “Additional resources” at the end of this article.)

The year 2020 has brought many new challenges and obstacles, including the expansion of SLF quarantine areas. The PDA expanded the quarantine zone to include 12 more counties this past April. Several of these counties are in central Pennsylvania, including Blair, Huntingdon, Mifflin and Juniata counties. I have conducted SLF treatments in the Altoona and Lewistown areas this year, which are located in those newly added quarantined counties. The SLF populations in both these areas were primarily along railroad beds. I no longer have to travel great distances from my home to treat for SLF – now I can see them in 10 minutes!

Controls

Having SLF this close to where I live this year was definitely exciting for me. Don’t get me wrong, I do not want them this close, but it does allow me to get more experience with them. My main systemic insecticide of choice is dinotefuran as a bark spray. There are many manufacturers of dinotefuran, but I chose one I have used in the past for other ornamental pests. I like to apply the solution with a low-pressure pump sprayer so as not to lose a lot of product by it “bouncing” off the bark. I also like to constantly walk around the tree to keep the application even and to prevent excessively spraying one area and causing runoff.

The label recommends applying the solution to the first four feet of the tree trunk, and I have found myself using all of that just to keep the solution from running off. The insecticide will start killing SLF that feed on the treated bark immediately, but as far as translocating throughout the tree, that all depends on many factors, such as temperature and how much precipitation has fallen recently. But it usually only takes a few days to spread throughout the tree.

SLF dead on the ground at the base of a tree.

One thing to keep in mind is that I am mostly treating ailanthus trees and only after they have dropped their flowers. As of now, there is no insecticide that only targets SLF, so any systemic insecticide that is applied will kill many different species of insects that feed on that tree. For this reason, it is important to apply when no flowers are present on the tree.

Along with creating trap trees with systemic insecticide on ailanthus trees, successfully eliminating unwanted ailanthus trees is very important. In order to persuade the SLF to go to the trap trees, you should eliminate other untreated ailanthus trees in the area. If you have any experience with this terrible tree, you know that if you have one ailanthus tree, you probably have many ailanthus trees!

Systemically treating ailanthus trees with an herbicide such as triclopyr is one of the most effective ways I have found to successfully eliminate ailanthus trees while reducing the amount of sprouting. The “hack-and-squirt” method works very well as a way to introduce the herbicide into the tree’s vascular system. I have found that “peeling” the bark like a banana with a sharp blade in order to expose as much of the cambium layer as possible works very well on this stubborn plant. If using the hack-and-squirt method, be sure to avoid girdling the tree completely; leave some living tissue to keep the tree alive enough to move the herbicide systemically.

I definitely have gained a lot of experience with applying pesticides for SLF, and it is fulfilling knowing I am helping to combat a serious problem here in Pennsylvania, as well as in the rest of the United States. I have been most amazed, though, by its effect on people. In the areas surrounding Berks County, which is ground zero here, the residents all seem to know about the SLF and share a common dislike for this unwanted pest. However, just two hours away in Mifflin County, where I have encountered a fairly large population along the railroad tracks, residents seem to have no clue what is brewing in the trees around them.

There is a small community located in Lewistown, Pa., that is close to the railroad tracks where I have been treating trees for SLF. The community center has an SLF poster in its window, but let’s be honest, most people won’t take notice of it. This community is surrounded by forests that are filled with ailanthus trees, as well as other tree species that SLF are attracted to. I feel it is only a matter of time before these residents are invaded and possibly overwhelmed by what is coming. This small community hosts Pee Wee Football games and has two playgrounds, which makes me wonder what will happen when the population of SLF in that area grows. I envision people trying to watch their kids play outside while constantly being harassed by the invader. Will it cause property values in that community to drop? I feel that only then will people realize the severity of the issue.

As of right now, one of the best things we can do is to educate as many people as possible about SLF. The general public’s awareness and reporting of any newfound populations is critical to the treatment and elimination of the SLF before the population in that area grows to where it cannot be eliminated. Hopefully, in the near future a better strategy will be developed, including biological controls.

Biological controls

In 2019, Penn State started to study two types of fungi that were found to attack and kill SLF. The fungi were found in the Berks County area and caused the death of many SLF in very specific areas. But we haven’t seen the fungi decimate large populations over a broad area, which is what is needed to really get a grip on SLF spread. My hope is that the fungi can be used to help find or create a solution in either the creation of a pathogen that moves freely through the SLF community or in a pesticide that targets SLF.

Effectively applying a biological pesticide could pose a problem as well, because the SLF spends a lot of its time on the lower parts of the tree, unlike another invasive insect, the gypsy moth, which can be targeted by aerial spraying when feeding on a tree’s foliage. To effectively apply a pesticide for SLF, it seems we will need “boots on the ground” to really get to the lower parts of the trees.

SLF will cling to many objects, not just trees.

There is some hope with natural predators such as praying mantis, birds and wheelbugs, but the populations of these predators aren’t large enough to really make a great impact. Parasitoids have been used in the past, such as with gypsy moth, but the introduction of any living organism would take a lot of research and most likely years for approval to ensure it can be safely introduced into our environment.

Conclusion

It is very possible we are still a few years away from a viable solution to the SLF problem. Until then, we have to do the best with what we have, and do some simple things that can make a difference, such as scraping egg masses, squishing as many as you can and reporting any SLF that are found, especially outside of an area that is already known to have them. The Penn State Extension website, https://extension.psu.edu/spotted-lanternfly, is an excellent source of information pertaining to SLF, including lists of pesticides that have been found effective for SLF treatment.

Additional resources

Pennsylvania Department of Agriculture (PDA), for their spotted lanternfly program:

https://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/spotted_lanternfly/Pages/default.aspx

U.S. Department of Agriculture spotted lanternfly webpage:

https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/sa_insects/slf

Lucas Markley is owner/operator of Markley Tree Care of Lewistown, Pennsylvania. He attended the Forest Technology program at Penn State Mont Alto, interned with the Pennsylvania Game Commission monitoring gypsy moth, worked as a forest insect pest aide at the Pennsylvania Department of Agriculture and was a plant healthcare specialist for Bartlett Tree Experts.

This article is based on a panel discussion he took part in, “Spotted Lanternfly: Get Ahead of It Now!” with Julie Urban at TCI EXPO 2019 in Pittsburgh, Pennsylvania. Click below to listen to an audio recording of that discussion.

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