Michael Haydn's Symphony No. 20 in C major, Perger 12, Sherman 20, MH 252, written in Salzburg in 1777, is one of the few of his symphonies to have a slow movement in a minor key, and one of his few C major symphonies to not include trumpets or timpani.
A. Delarte, "A Quick Overview Of The Instrumental Music Of Michael Haydn" Bob's Poetry Magazine November 2006: 20 PDF
Charles H. Sherman and T. Donley Thomas, Johann Michael Haydn (1737 - 1806), a chronological thematic catalogue of his works. Stuyvesant, New York: Pendragon Press (1993)
C. Sherman, "Johann Michael Haydn" in The Symphony: Salzburg, Part 2 London: Garland Publishing (1982): lxviii