All loyal sons (and daughters) of Erin (and those who’d like to be) will be on hand for the “20th Annual Washington D.C. Irish Folk Festival,” which takes over Wolf Trap today. Once again, the event is divided into two segments, an afternoon program and an evening concert. The former consists of small concerts and workshops featuring two bands representing the next generation of Irish folk stars, Dervish and Nomos, as well as Seámus Egan’s Irish-American supergroup, Solás, local heroes Celtic Thunder, multi-instrumentalist Zan McLeod, and scores of others. The latter, hosted by Fiona Ritchie (of National Public Radio’s Thistle and Shamrock show), also stars Dervish, Martin Hayes, and Solás, as well as the marvelous Scottish singer Andy M. Stewart (ex-Silly Wizard) and famed quartet Patrick Street (Kevin Burke, Andy Irvine, Jackie Daly, Ged Foley). The early program runs from 11 a.m.-5 p.m.; the evening concert begins at 8 p.m. at Wolf Trap Filene Center, 1624 Trap Rd., Vienna. $18. (703) 938-2404. (KR)