It's Week 18 of 20 for the Medford Farmers Market at the Condon Band Shell Park, but due to Covid-19 restrictions, the live music again will be presented online. Performing will be Mark Abruzzese from 5 to 6 p.m., and the Boston String Band from 6 to 7 p.m. Tune in on the Farmers Market Facebook page: https://www.facebook.com/MedfordFarmerMkt/ Onsite vendors this week will be Bart's Ice Cream, Beads by Beardslee, Bread Obsession, Brigham Farm, Deano's Pasta, Deershorn Farm, Elzire's Acre…