The word "discoed" is spelled with a silent "e" at the end, which indicates a long vowel sound in the previous syllable. Specifically, the "o" in "disco" is pronounced as a long "o" sound /oʊ/ rather than a short "o" sound /ɑ/ because of the presence of the silent "e". The addition of the suffix "-ed" then creates the past tense of the verb "disco", resulting in the word "discoed", pronounced as /ˈdɪskoʊd/.
* The statistics data for these misspellings percentages are collected from over 15,411,110 spell check sessions on www.spellchecker.net from Jan 2010 - Jun 2012.