MOND explains the rotation curves of galaxies extremely well; Dark
Matter explains the same things not so well. Dark Matter explains
galactic cluster interactions extremely well; MOND explains the same
things not so well. That's the long and short of it.

/Dark Fields/ is an attempt to make MOND work better at the cluster
level. There is a lot of cajoling needed to make Dark Matter work well
within the galactic scale too. So it looks like neither theory works
well outside their on size scale.

SPACE.com -- Dark Horse Challenges Dark Matter to Explain Missing Matter
"When applied to just galaxies, MOND can predict very well the behavior
that astronomers observe. But when MOND is applied to larger structures
like clusters of galaxies, it fails. To make MOND work for clusters, it
must include more complicated concepts, such as entities called dark
fields, which are different from dark matter, but work in a similar way
to alter the amount of gravity present."
http://www.space.com/scienceastronom...ng-matter.html

Yousuf Khan