New York Jungle Zombies

METEORS, OVERGROWN PLANTS and... ZOMBIE ANTS???
When a meteor crashes in the middle of Central Park, Austen and Kyrsten both find their curiosity piqued. Investigating the site quickly reveals that the meteor is more than it seems. It is a giant seed, and vines are growing out of it at an exponential rate. The vines will take over Manhattan within 24 hours if someone doesn’t do something. The only problem is, the city’s been evacuated, and the only ones who can stop it are the two children. However, it’s a little hard to get some weed killer, when you’re also being chased by zombies.
How can Kysten and Austen stop the seed from taking over the city without getting turned into zombies themselves?