to cover something with weeds, or for wheat or the like to choke out the weeds (?) (see Molina)
Alonso de Molina:
xippachoa. nitla. cubrir algo de yerua, o ahogarla yerua el trigo, o cosa semejante. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 159r. col. 2. Thanks to Joe Campbell for providing the transcription.