The headword is either masculine accusative singular or (more probably, given what follows) neuter nominative/accusative singular of the adjective μαλερός .
[1] Photius has the same glosses, though for the Suda's hapax σποδόεν Photius has σπουδαῖον "serious, severe" -- which Theodorides puts in cruxes; see his discussion at vol.II p.LXVII. Hesychius has "intense, bright, strong, weak", as well as "withering"; "withering" is given by more ancient authorities (Philoxenus fr. 673, cited in Orion [Author, Myth] and the Etymologicum Magnum; scholia to Hesiod, Theogony 16; scholia to Oppian, Halieutica 1.300).
[2] LSJ s.v. μαλερός notes μαλερὸν πῦρ as a Homeric expression (Iliad 9.242, 20.316, 21.375). Photius also includes these examples. The seemingly contradictory meaning for μαλεραὶ φρένες is noted in LSJ only for this fragment (found only here and in Photius), which they attribute to Callimachus; it is Supplementum Hellenisticum 1087, and Lloyd-Jones and Parsons treat it as unattributable.
[3] Greek Anthology 6.207.4.