SLF (Spotted Lanternfly) is native to China, India, and Vietnam. They were first sited in the USA around 2014 in Berks County, Pennsylvania originating from shipping containers and have been spreading ever since. SLF feeds on the sap of plants which weakens them and makes them more susceptible to diseases. SLF also excrete honeydew which promotes black sooty mold. SLF is known to feed on 70 plant species including apples, cherry, chestnut, hops, maple, peaches, pear, pine, plum, poplar, oak, rose, and walnut.
SLF preferred host is TOH (Tree-of-Heaven) which is native to China and considered a noxious weed in the northeastern USA. TOH is not on the list of top invasives in NJ and is labeled as moderately invasive in a 2013 NY study. This is surprising because TOH can be seen everywhere while driving around the NYC area. TOH produces allelopathic chemicals in its leaves, roots, and bark which can limit or prevent the establishment of other plants. It is believed that TOH is the preferred host of SLF because the insects can utilize the allelopathic chemicals in TOH to ward off predators. The chemicals give the SLF a bitter taste which makes them less likely for potential predators, such as birds, to eat them.
It has been estimated that SLF has already caused millions of dollars of damage to the agricultural industry and is predicted to continue doing so. As of 2021, certain counties in PA, NJ, and NY with SLF infestations have established quarantines that restrict the transportation of certain materials that could be carrying SLF such as firewood. There is a lot of information out there on SLF since it is such a problem in the tri-state area. For more information on SLF, check relevant government agencies of the infested states such as the Pennsylvania Cooperative Extension, New Jersey Department of Agriculture, and the New York Department of Conservation.
The first time I saw an SLF was in the summer of 2020 while working at Profeta Farms in Readington NJ. Fortunately, the farm did not grow any crops that SLF feed on. So the SLF would feed on TOH that grew in between fields and would hang out on the sides of buildings. I was always worried about inadvertently transporting SLF back to Jersey City or Upstate NY. Because of this, I would always check my car for SLF before driving back from work. In late Spring of 2021, I started seeing SLF nymphs around Jersey City. I started squashing and reporting them as requested by the NJ Dept of Ag. By the end of the summer, I was starting to see lots of adult SLF everywhere around Jersey City. However, Hudson County had not been put on the New Jersey SLF quarantine list as of the Fall of 2021. It was in the Fall that I started to notice SLF climbing up the 3.5-foot DBH (diameter at breast height) TOH in Riverview Community Garden. This is the time of the year in the SLF life cycle when they lay their egg masses so my guess is they started coming to the tree for that.
All professional recommendations for dealing with this issue would be to remove the TOH from the garden. However, because of its size, the TOH is beloved and has become a staple in the garden so it would be preferred to save the tree if possible. Trees with over three feet DBH are very rare in Jersey City so this TOH really stands out. Although, it is nowhere close to the recorded largest TOH in the world. It is difficult to estimate how old the tree is since I have not been able to find the growth factor of TOH used in online calculators. TOH life span is usually short-lived, from around 30 to 70 years. However, cloning from root sprouts has been known to extend life greatly. It is possible that this tree was a clone and much older than 70 since TOH has a history of being a highly desirable cultigen in NYC. However, TOH has been known to reach this size in as little as 30 years. Another reason to save the tree is because of the large crown that it has. Not only does the crown provide a foundation for the local ecosystem, it also has many other benefits to urban areas. As of 2021, Jersey City is having a tree canopy deterioration crisis so removing a very mature shade tree does not seem to be in the best interest.
So how do you defend a 40-foot tall tree from SLF? The short answer is it’s not easy. PSU put out a great management guide for SLF. I started IPM (integrated pest management) for the TOH by squashing the SLF on the lower part of the trunk every day. SLF do not fly, they are planthoppers so they jump and glide. They usually are at the bottom of the tree trunk to begin their ascent up. Since the tree is so tall, the only real opportunity to defend the tree from SLF is when the insects are crawling on the first ten or so feet of the trunk. The SLF jumps quickly when you go to squash them. I realized that SLF will only jump forwards. So if you come at the SLF from the front of them, they will jump into what you are squashing them with. I used a small piece of cardboard as a flyswatter. For SLF that were above my arm’s reach, I use a piece of wood to reach as high up as I could. Doing this would usually not be fast enough to squash them but it would make them glide down to the ground where I would then squash them with my shoe. SLF bodies are very soft and easy to squash if you are able to make contact with them. I also scraped off egg masses I was able to reach. However, SLF prefer to lay egg masses on smoother bark higher up in the tree.
Eventually, it seemed like going over to the tree once a day to squash SLF and scrape egg masses was not enough. I started seeing more SLF and egg masses higher up in the tree where I could not reach. The next thing to try was a trap so I could kill SLF while I wasn’t in the garden. The PSU recommended circle trap did not seem suitable because of the 11-foot circumference of the tree. So I tried wrapping agricultural-grade flypaper around the tree. This did not turn out to be very effective because of how mishappen the trunk was to a smooth circle. As a result, there would be spaces under the flypaper where the SLF could crawl right past. It would really only catch the SLF that jumped directory onto the flypaper. Also, the flypaper could potentially trap birds, bats, or beneficial insects so it seemed like it would do more harm than good. Then I found the BugBarrier which solved all issues with the flypaper.
The next IPM technique to try is biocontrol which we can do by providing habitat for natural predators. To create a habitat for wildlife, you must provide food, water, shelter, and space. The National Audubon Society put out a great article on documented natural predators of SLF. Birds such as the red-bellied woodpecker have been known to eat SLF. The community garden is a certified wildlife garden so it provides excellent habitat for birds. Other natural predators of the SLF are mantises and spiders such as the Chinese mantis and the spotted orb-weaver. Spiders like to build nests on tall plants. Mantis like living where there is prey, which spiders are one of. So if you can attract spiders, you can attract mantises as well. Unfortunately, because of the giant TOH, it will make it more difficult for predators to eat the SLF because of the allelopathic chemicals in the TOH which the SLF eat.
This article has some other interesting ideas to try before resorting to synthetic chemicals. There are also native fungi that have been known to kill SLF. Fortunately as of 2021, the SLF infestation on the TOH is not that bad as seen in other places, there aren’t 1000s of them crawling on the tree yet.