Spotted lanternfly on apple in Berks County, PA in October 2017. Photo: Erica Smyers, Penn State
The Spotted Lanternfly (Lycorma delicatula) (SLF) is an invasive insect pest dangerous to the U.S. fruit and forest industries. It was first detected in September 2014 in Berks County, PA by the Pennsylvania Department of Agriculture and the Pennsylvania Game Commission. In three years the SLF quarantine zone has expanded to 6,900 square miles, and it was recently detected in Delaware and New York, becoming a regional and potentially national pest.
Management strategies are needed to slow its spread to other regional fruit growing centers and to provide fruit growers with timely management tactics. This phloem-feeding Asian-native insect feeds upon over 65 species of plants and as such, is projected to become a serious pest of timber, ornamental trees, tree fruit orchards, grapes, stone fruit, and other small fruits such as blueberries. It can kill hops and feeds on several types of vegetables. SLF honeydew (sugary SLF excrement) and sooty mold (growing on honeydew) damage were found in vineyards in 2016, only two years after first detection.
In 2017, extensive sooty mold growth was observed on and around forest trees, such as tree of heaven, willow, and maples, and blackening of adjacent plants in the forest understory. Black walnut feeding caused yellowing and shocked trees into a general decline. SLF spread to more vineyards in 2017, reducing yield in one, and having as yet unknown long term effects on health of grapevines. In late August, for the first time, large numbers of SLF were observed flying into and feeding on the trunks and branches of apple trees as well as nectarines and peaches. Immediate damage to tree fruit was not observed by the immigrating adults, but SLF egg cases found on the trees put the trees at risk for heavier and more sustained feeding by SLF nymphs and adults in Spring 2018. As an invasive pest in South Korea, SLF spread rapidly and caused significant wilting, dieback and mortality of grape vines and spread throughout the country in only 3 years.
Sooty mold on rocks and base of Ailanthus tree with SLF infestation. Photo: Emelie Swackhamer, Penn State
There are large gaps in our current understanding of SLF biology in the U.S. These must be filled in order to manage this pest effectively. Alternate hosts, reproductive requirements, pesticide susceptibility, nutritional requirements, pheromone communications, flight distances, voltinism, diapause requirements and other biological aspects are unknown for the U.S. population. Egg cases are laid on hard surfaces like tree bark, but also vehicles, rail cars, and shipping palettes portending rapid and distant spreading by man rather than due to the limited flight abilities of SLF adults or to the hopping abilities of the nymphs. Cold temperatures that proved lethal to SLF eggs in Korea apparently are not lethal to U.S. SLF, making most of the U.S. suitable habitat for SLF.
The SLF invasion is similar to another recently invasive pest, the brown marmorated stink bug, which caused $37 million in damage to the mid-Atlantic fruit industry in 2010. Like SLF, BSMB has many alternate hosts, quickly spread to surrounding states and eventually to the West Coast and Europe. While SLF does not feed on fruit like BMSB, it has the potential to mechanically vector diseases such as fire blight in apple and cause a general decline of tree and small fruits through loss of vigor or systemic feeding shock similar to that seen from high populations of pear psylla on pear trees in what is referred to as ‘psylla shock’. SLF also has only a single generation each season and at least currently spends most of its life cycle outside the orchards in natural areas, moving into orchards and vineyards as adults in huge numbers in the late fall like BMSB. We say ‘at least currently’ because what little is known about its biology in Asia has not helped much in predicting its behavior in Pennsylvania and because in at least one vineyard in Berks County, SLF has been found in all stages from spring to fall within the vineyard.
We are proposing a collaboration among regional planthopper specialists, applied grape and tree fruit entomologists, and extension educators as well as Dr. Tracy Leskey, USDA-ARS Appalachian Fruit Research Station, Kearneysville, WV, who has led over ten years of research on BMSB management through a previous USDA grant which several of the researchers were a part of. We will develop IPM tactics to address short-term control needs as well as more basic biological research for longer term solutions. Spinoffs from these efforts in fruit should also help in nuisance control from homeowners plagued with huge numbers SLF in the quarantine zone and for the timber and ornamental industries.
Potential Economic Impacts
Slowing the spread of SLF will protect multiple industries. The Pennsylvania grape industry is a thriving and multi-dimensional commodity with over 12,000 acres under production. In the U.S., PA is the 5th largest producer of wine grapes and third largest producer of juice grapes as well as the 4th and 5th largest producers of apple and peaches respectively with tree fruit and small fruit production valued at over $100 million. The U.S. is the world´s second largest producer of apples with an estimated farm gate value of $3.5 billion and downstream economic impact of $14 billion. Roughly 25% ($954 million) of fresh apples are exported. A SLF quarantine could threaten this export market. Forests comprise 17 million acres in Pennsylvania, which is the largest producer of hardwoods ($5.5 billion annually) in the U.S. and is also at risk of SLF damage and export restrictions. Damage to the trees and understory plants (from sooty mold growth) may affect wildlife populations and decrease resistance to plant disease. Although too early to assign economic value, the potential economic impact of SLF in the U.S. could be staggering.
Spotted lanternfly adults on grape in Berks County, PA in October 2017. Photo: Erica Smyers, Penn State
On October 18, 2017, a joint hearing of the Pennsylvania Senate and House Agriculture and Rural Affairs Committee addressed the Spotted Lantern Fly outbreak. Testimony was given by the Pennsylvania Department of Agriculture (PDA), Penn State research and extension, and county administrators and fruit and wine growers from the SLF quarantine zone. Fruit growers and homeowners in the quarantine zone already plagued by huge numbers of SLF and those who fear they will be invaded are adamant about developing cultural or chemical control methods. Testimony from the owners of an affected winery and grape/tree fruit orchard describe an almost 90% loss in grape tonnage and a corresponding loss in fruit quality which was valued at one farm at $400,000, despite several pesticide spray applications. They testified that they needed all possible help in the form of pesticide control recommendations and research for biological control options in order for them to remain in business in coming years due to SLF. Special concern was expressed about the effect that heavy feeding in 2017 would have on the winter hardiness, disease susceptibility and vectoring, and long term viability of vines and trees affected by heavy feeding.
Grape and fruit growers that have already seen greatly increased spray bills due to the invasive BMSB 10 years ago, have expressed concern about increased spray costs, issues with marketing a product in a quarantine zone, the impact of increased pesticide use on current IPM programs that would cause flare-ups of secondary pests such as mites and aphids that would require additional non-SLF sprays, or the use of pesticides that could cause harm to managed and native pollinators.
Translating information and delivering actionable products to end-users:
Development of actionable recommendations for growers and homeowners affected by SLF is the core goal of our regional project. We will develop an integrated monitoring and management program for specialty crops that will integrate SLF management with management of other insect, mite, and disease pests. At its core will be a web-based decision support tool linked to an interactive map. As SLF populations change, geo-referenced farms will be notified and recommendations will be made. This tool can be used by growers and their advisors to predict consequences of different pest management scenarios on costs and benefits to crop yield or quality, and provide a confidence level in those predictions (i.e., uncertainty is represented). We will use comparisons between observations and model predictions to update the model, using a “big data”, adaptive management approach to continually improve its predictions. As a result, each time the online decision-support tool is used, predictions will reflect new knowledge gained from coordinated data collection. In short, our goal is to gather and curate data in order to improve the accuracy of decisions continually over time. What we learn from SLF biology, economic injury, and management with both pesticides and biological control will be presented to farmers/land managers in a practical way they can use to manage and slow the spread of this pest.
Spotted lanternfly on apple in Berks County, PA in October 2017. Photo: Erica Smyers, Penn State
Penn State graduate student Erica Smyers studying under Julie Urban and Mike Saunders on SLF adults has developed preliminary pesticide control data using grape insecticides. She has shown in caged studies in the quarantine zone that SLF appears to be much easier to control than BMSB with the best control coming from neonicotinoid products such as Venom, Actara, and Assail as expected, but also excellent control with contact poisons such as Sevin, Malathion, and Imidan. Unlike with BMSB, however, the pyrethroids were somewhat weaker at controlling SLF adults with some variability between products. Of the organic products tested, Insecticidal Soap gave the best control, with Neem and Natria (sulfur and natural pyrethrin) being somewhat weaker. Growers within the quarantine zone have also observed that SLF is not that hard to control, but that residual activity of insecticides was important due a constant influx of new adults into treated areas. We will make this data available in a future Fruit Times article along with a preliminary rating of homeowner pesticides that were also tested on SLF adults.
Special thanks to the Pennsylvania Department of Agriculture and Sven-Erik Spichiger in particular for sharing information and presentations on SLF to us and to research and extension in recent fruit grower meetings.