Spotted Lanternfly on Figs and Grapes - Ask Extension
I've read much of the info and resources on your website and have a couple questions/suggestions based on my own and my neighbors' experiences. I have...
Knowledgebase
Spotted Lanternfly on Figs and Grapes #871136
Asked June 02, 2024, 12:08 PM EDT
I've read much of the info and resources on your website and have a couple questions/suggestions based on my own and my neighbors' experiences. I have infestations on my own grapevine and fig trees and neighbors here in Violetville are contacting me as a master gardener about what to do. Some also have grapes and figs; others simply have them in their yard.
Attached are a few photos:
1) one example of several spots of infestation on my 2 young fig trees and 80 year+ old grapevine.
2) one of two app. 1.5 ft fig tree branches found dangling from the tree. Unless an acrobatic squirrel selectively jumped through the dense fig tree foliage to land on those branches 2 days in a row to break them off, it seems possible the sap might have been sucked from the juncture where the branch joined the tree, thereby weakening the branches? That is conjecture based on finding them the same time as the high infestation. What do you think?
3) damage to leaves which may be from the nymphs or from the dish soap spray I used.
My question/suggestion - as home gardeners (and master gardeners), we need realistic advice. Scrape and smash can work with eggs or on a tree or something with a hard surface, but not when they are on leaves and small branches behind more leaves and small branches.... My neighbor found that vacuuming his grapevine was incredibly tedious and we've both found that trying to swat them off into a jar of soapy water/alcohol is also not realistic when they hop away as soon as we approach.
So, I searched for other options and found Table 6 of the Penn State Guide referenced on your website with info about less toxic contact insecticides and the Montgomery NJ info about DIY household sprays.(links below) I needed something immediately so opted for the dish soap-oil-water combo but then unsuccessfully searched for more info about whether a light spraying before they hopped away would kill them or whether they needed to be drenched... And which is better for the plants - the dish soap or the vinegar? Apparently no research and you all do not recommend such home remedies.
My concern - those of us who do not want to use sprays but are forced to need as much info as possible about which are most effective while least toxic to the plants themselves and to other wildlife. The Penn State resource (Table 6) provides a very basic overview of that for commercial products but does not reference DIY home remedies. And the contact insecticides they suggest have only sparse info about them. So am I to assume the home remedies do not work and I need to search for the pyrethrins or neem oil or insecticidal soap? And which of those is most effective while least toxic for grapes and figs?
https://extension.psu.edu/spotted-lanternfly-management-guide, Table 6
https://www.montgomerynj.gov/bc-stc/page/ways-fight-spotted-lanternfly
As I'm writing this I just got another text from 2 neighbors with "a serious infestation." If I can't tell them more specific info about less toxic options, I fear they will resort to area wide spraying....
Baltimore City County Maryland
Expert Response
The early messaging from the Maryland Department of Agriculture's Spotted Lanternfly (SLF) control campaign was to physically kill (squish) any of the insects seen in order to slow their spread into new areas. Plus, it was unknown in the early days of SLF invasion how much damage they could do to natural areas and home garden plants, so MDA was erring on the side of caution to prevent their establishment. Now that SLF is found nearly state-wide (and region-wide), that type of rigorous management is less applicable because it's no longer affecting SLF spread locally, and biologists also now know through years of study and observation that SLF does no serious harm to the vast majority of home landscape or farmland plants. (Grapevine and hops being notable exceptions, but even then, it largely is a risk to farms and vineyards more than home garden settings and research is inconclusive as to whether or not they detriment the plants or the harvest quality.)
Even thorough and successful control of easy-to-reach egg masses, nymphs, or adults will not suppress the SLF population in the area, and is only a very temporary measure. For one, many of the insects will simply be out of each or out of sight to spray or squish, and the majority of their egg masses each winter are similarly well outside of scraping range, high in tree canopies. Since nymphs jump readily and adults can also fly, they are able to recolonize an area that might have temporarily eradicated them via physical or chemical means. Fortunately, a range of natural enemies (beneficial insects and birds, for example, that prey on SLF) is increasingly learning to consume them. (Granted, areas on the forefront of the spread of SLF, outside of Maryland and in the few MD counties with no detected populations yet, should still be vigilant and try to slow spread into new areas.)
Both the MDA and UMD Extension do not recommend using any pesticide to manage SLF in residential settings. There is no product that is used to kill SLF that will not risk harming other insects or organisms that the treatment comes into contact with. Horticultural oil (neem being one type) and insecticidal soap are among the lowest-toxicity options when they are warranted, but even they can kill beneficial insects if the spray contacts them directly; dried residues are not effective, either for the target pest or other insects. Pyrethroids are not recommended because they are much more hazardous to non-target insects; they last longer than the organic alternative pyrethrum, but in both cases, they are still broad-spectrum insecticides.
We do not condone the use of home remedies instead of registered, labeled pesticides. Penn State has a good web page outlining the many ways that home remedy / DIY pesticides can be harmful (or at the very least ineffective). The leaf damage on the fig pictured does look like phytotoxicity (plant tissue damage from chemical exposure), likely caused by the soap and oil spray you mention using. That leaf damage was not caused by SLF.
Dish soap and other household detergents that are not formulated for use on plants can strip the protective wax layer off of foliage, causing desiccation or the type of "burn" you experienced. Even though insecticidal soaps have "soap" in the name, they are designed for use on live plants and have other ingredients not listed on the bottle that contribute to this intended use.
Household vinegar is a weak concentration of acetic acid; it's mostly water, and would have little impact on insects, though still might burn plants if they are also heat- or drought-stressed. Horticultural-strength vinegar is a much stronger acid and is used as an herbicide, not insecticide, for the very reason that it causes significant plant damage. It is also very caustic and could cause skin damage or severe eye damage if not used with caution and sufficient personal protective equipment (PPE). Gardeners sometimes think that vinegar, being a familiar ingredient, is somehow less risky or toxic than labeled pesticides, but that is not the case.
No pesticide of any type should be used on a plant that is grown for harvest unless the label specifically allows for its use on edible plants. (In such cases, they'll usually give specific dosage information for each crop, like grapes, cherries, etc., listed individually.) Even if the active ingredient is the same between two products (same chemical, same concentration), one labeled for crops and one not, the inert ingredients between them might not be the same. Since manufacturers are not required to list every inert ingredient (though they must choose from EPA-tested chemicals), there is no way to know if they are exactly the same or not.
Broken fig branches are not caused by SLF, and the wood was not weakened by sap removal. (If sap flow had been interrupted, the branch tip would simply have wilted or scorched and died back.) Squirrels can indeed be very acrobatic -- they can jump horizontally about 10 feet, and can also hang upside-down readily when consuming berries and bird seed, snipping leaves or twigs off for nesting material, and so forth -- but twigs can be snapped off by wind or other wildlife as well. There are some beetles that neatly chew off branch tips, but they would be present on trees like oak, not fig.
For any plant that is compact enough, the simplest approach to excluding SLF (if desired) is to cover it with either crop row cover or insect mesh netting before the nymphs hatch. Grapes should still set enough fruit without bee pollination, since you will need to keep the cover on the plant(s) all season until ready to harvest. Some products of insect mesh are made quite large, to envelop one or more large blueberry bushes, for example, so should be large enough to cover a grapevine.
We maintain a Spotted Lanternfly Management for Residents web page, and will be updating it soon regarding placing emphasis on not using insecticide. The take-home message for home gardeners is this: SLF can become abundant as the population swells, but they are not going to cause serious damage to your plants, and no intervention (especially not with pesticide) is necessary. As with any IPM approach, use a chemical intervention last, and only when other attempts at pest control have failed and when the plant is suffering too much damage to ignore.
Miri
Even thorough and successful control of easy-to-reach egg masses, nymphs, or adults will not suppress the SLF population in the area, and is only a very temporary measure. For one, many of the insects will simply be out of each or out of sight to spray or squish, and the majority of their egg masses each winter are similarly well outside of scraping range, high in tree canopies. Since nymphs jump readily and adults can also fly, they are able to recolonize an area that might have temporarily eradicated them via physical or chemical means. Fortunately, a range of natural enemies (beneficial insects and birds, for example, that prey on SLF) is increasingly learning to consume them. (Granted, areas on the forefront of the spread of SLF, outside of Maryland and in the few MD counties with no detected populations yet, should still be vigilant and try to slow spread into new areas.)
Both the MDA and UMD Extension do not recommend using any pesticide to manage SLF in residential settings. There is no product that is used to kill SLF that will not risk harming other insects or organisms that the treatment comes into contact with. Horticultural oil (neem being one type) and insecticidal soap are among the lowest-toxicity options when they are warranted, but even they can kill beneficial insects if the spray contacts them directly; dried residues are not effective, either for the target pest or other insects. Pyrethroids are not recommended because they are much more hazardous to non-target insects; they last longer than the organic alternative pyrethrum, but in both cases, they are still broad-spectrum insecticides.
We do not condone the use of home remedies instead of registered, labeled pesticides. Penn State has a good web page outlining the many ways that home remedy / DIY pesticides can be harmful (or at the very least ineffective). The leaf damage on the fig pictured does look like phytotoxicity (plant tissue damage from chemical exposure), likely caused by the soap and oil spray you mention using. That leaf damage was not caused by SLF.
Dish soap and other household detergents that are not formulated for use on plants can strip the protective wax layer off of foliage, causing desiccation or the type of "burn" you experienced. Even though insecticidal soaps have "soap" in the name, they are designed for use on live plants and have other ingredients not listed on the bottle that contribute to this intended use.
Household vinegar is a weak concentration of acetic acid; it's mostly water, and would have little impact on insects, though still might burn plants if they are also heat- or drought-stressed. Horticultural-strength vinegar is a much stronger acid and is used as an herbicide, not insecticide, for the very reason that it causes significant plant damage. It is also very caustic and could cause skin damage or severe eye damage if not used with caution and sufficient personal protective equipment (PPE). Gardeners sometimes think that vinegar, being a familiar ingredient, is somehow less risky or toxic than labeled pesticides, but that is not the case.
No pesticide of any type should be used on a plant that is grown for harvest unless the label specifically allows for its use on edible plants. (In such cases, they'll usually give specific dosage information for each crop, like grapes, cherries, etc., listed individually.) Even if the active ingredient is the same between two products (same chemical, same concentration), one labeled for crops and one not, the inert ingredients between them might not be the same. Since manufacturers are not required to list every inert ingredient (though they must choose from EPA-tested chemicals), there is no way to know if they are exactly the same or not.
Broken fig branches are not caused by SLF, and the wood was not weakened by sap removal. (If sap flow had been interrupted, the branch tip would simply have wilted or scorched and died back.) Squirrels can indeed be very acrobatic -- they can jump horizontally about 10 feet, and can also hang upside-down readily when consuming berries and bird seed, snipping leaves or twigs off for nesting material, and so forth -- but twigs can be snapped off by wind or other wildlife as well. There are some beetles that neatly chew off branch tips, but they would be present on trees like oak, not fig.
For any plant that is compact enough, the simplest approach to excluding SLF (if desired) is to cover it with either crop row cover or insect mesh netting before the nymphs hatch. Grapes should still set enough fruit without bee pollination, since you will need to keep the cover on the plant(s) all season until ready to harvest. Some products of insect mesh are made quite large, to envelop one or more large blueberry bushes, for example, so should be large enough to cover a grapevine.
We maintain a Spotted Lanternfly Management for Residents web page, and will be updating it soon regarding placing emphasis on not using insecticide. The take-home message for home gardeners is this: SLF can become abundant as the population swells, but they are not going to cause serious damage to your plants, and no intervention (especially not with pesticide) is necessary. As with any IPM approach, use a chemical intervention last, and only when other attempts at pest control have failed and when the plant is suffering too much damage to ignore.
Miri
Thanks very much for the detailed response. While I’m desperately trying to save my grapes and figs, it is definitely helpful to put this issue into a bigger picture, especially given how overwhelming and impossible it is to think about how to slow them down while trying to figure out how to coexist until an alternative can be found. I’ll try to figure out how to convey some of these concepts to neighbors as well.
You're welcome.
