Sorry to hear about possible SLF damage to your grapevine! Our extension is happy to work with you. However, since Ask Extension is remote, i.e., on-line, sending in photos of the plant are very helpful to addressing the specific issues and troubleshooting. Could you please send photos?

The good news is that the areas in PA where SLF first appeared are possibly seeing a decline in SLF numbers, so there is hope that enhancing our garden practices and natural predators can keep our gardens thriving!

As to grapes, there are many types/species of grapes grown in DC gardens, many are table grapes like those grown commercially, but some are native such as Muscadines, etc. General practices are similar, but knowing what type of grape would be helpful.

Although SLF can hit grapes hard, the good news is that some local predators are feeding on SLF, so we can hope that management can keep populations down to levels grapevines can tolerate, and nymphs are usually seen in May, so taking action in April is still timely. https://extension.umd.edu/resource/spotted-lanternfly-home-gardens/

In the meantime, there are non-site-specific steps to reduce SLF populations dramatically.

1. Remove eggs: Using a plastic credit card, paint scraper, etc., scrape off egg cases on and near the grape vine into a container. Also check nearby surfaces & trees. Then cover the eggs with rubbing alcohol, then discard. 
https://extension.psu.edu/spotted-lanternfly-management-in-vineyards

2. Remove any Tree of Heaven on your property, Ailanthus altissima, which is an invasive plant & a preferred SLF host. It has some native tree lookalikes some as Black Walnut & Staghorn Sumac. Feel free to send photos for help distinguishing, and here is a link with details: https://extension.psu.edu/tree-of-heaven-native-look-alikes

3. For commercial vineyards, which are fenced away from the public and have far too many vines to hand-manage, there are recommendations for control sprays incorporated in the vineyards regular spray program. However, for home gardens, and most certainly in open public spaces, we would recommend IPM (Integrated Pest Management), which is long-term control,  and would not recommend use of pesticides, which are costly, short-term and pose hazards, https://ipm.ucanr.edu/what-is-ipm/#gsc.tab=0

4. Netting wrapped around grapevines has been shown to nearly eliminate SLF 
feeding! However, it is not set it and forget it; it needs to be tight enough to exclude SLF (& of course to avoid by-trapping birds), requires monitoring to remove any SLF that emerge from missed egg masses under the netting, and timed to allow pollination. So netting entire vines might be a preseason and post season measure for home gardeners. However, brown bagging fruit clusters is less costly practice to protect fruit to reduce diseases as well as insects.

5. Bagging grapes & more tips on growing grapes in the home garden: 

6. Monitor other plants over the season. Spraying nymphs off the plants is an effective control. In our humid climate it is advisable to spray down early in the day so that leaves can dry off before evening. Avoid leaving grape vines damp.. Knocking nymphs into a container of water (with a few drops of Castile liquid  soap to break water surface tension) then covering with a lid to prevent escape can help chedk population growth. Anecdotally, some gardeners have found small portable hand vacuums useful for catching nymphs, then dumping into the soapy water to drown.

7. Make (or even buy) and deploy SLF traps on your grapevine trunk if on an arbor, trees, etc., that have screening to prevent accidentally catching birds and other beneficials, to prevent SLF nymphs from climbing up into your grapevine. https://extension.rutgers.edu/spotted-lanternfly/management-trapping

8. Plant a border of flowering natives and herbs to attract beneficials, such as insect predators to your yard. 

9. Additionally, there are reports of birds feeding on SLF, so anecdotally, maintaining a clean birdbath during the day could serve to attract birds to your yard. Would recommend emptying the birdbath at dusk & refilling in early hours to prevent rats taking advantage of the water source. If you have the budget for it, one of those invisible ponds with a fountain on a timer/solar pump can provide water during the day, but not at night. Happy to provide further details if interested.

10. Rats need to be excluded for the vine to thrive and for general health concerns. https://www.dcratsolutions.com/ Recommend starting with diligence in making sure no food is available at any time by joining DC’s food waste pickup, not putting any food waste in trash cans in alley, no bird feeders, no feeding pets outside, no pet waste in yard, no water available outdoors at night, dropping off food waste at DC food waste collection stations and Farmers’ Markets. https://zerowaste.dc.gov/foodwastedropoff and washing off any recyclables before putting into bins. Strive to put out trash as close to pickup as manageable. Clear away cover that allow burrowing, and run a hose on trickle to soak into any suspected burrowing areas far away from the house to avoid any flooding issues. Monitor for activity and remediate as needed until no activity is present. Make sure that grape clusters are bagged, and that no fruit is left on the ground or otherwise accessible.
Any burrows in the alley can be reported to DC

Hope these tips are helpful and look forward to working with you further. Please send photos, if you can, they are very helpful in addressing specific needs of your site. And please keep us posted!

Many thanks,

KatieMacDC UDC volunteer team