Racquet Art Daub-it Empty bottles with applicators - 8 oz - Mohair dauber - 2 Pack

https://www.ruralking.com/41-glyphosate-grass-and-weed-killer-1-gallon-05200-101 https://a.co/d/0538FpnU For ~$45 + $15 if you want dye https://a.co/d/08DSDnL8 Mix 50% glyphosate and 50% water in dauber.

It looks like a Bradford Pear sapling to me. There are tough to kill. I have them coming up all over my yard from a bradford pear I took down two years ago where the root continue to resprout. I treat mine with a 50/50 mix of triclopyr and glyphosate. You can buy a dauber (https://www.amazon.com/Racquet-Art-Daub-bottles-applicators/dp/B09QSZT54J) to control where the herbicide ends up (or you can spray if you don't care about the grass). If this is Bradford Pear, be prepared for a long battle - these things resprout for years.

https://www.amazon.com/dp/B09QSZT54J?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1 These are the ones I use, they're literally perfect!