  Existence of color sextet diquark Higgs fields with TeV masses will indicate
a fundamentally different direction for unification than conventional grand
unified theories. There is a class of partial unification models based on the
gauge group $SU(2)_L\times SU(2)_R\times SU(4)_c$ that implement the seesaw
mechanism for neutrino mass with seesaw scale around $10^{11}$ GeV, where
indeed such light fields appear naturally despite the high gauge symmetry
breaking scale. They couple only to up-type quarks in this model.
  We discuss phenomenological constraints on these fields and show that they
could be detected at LHC via their decay to either $tt$ or single top + jet. We
also find that existing Tevatron data gives a lower bound on its mass somewhere
in the 400-500 GeV, for reasonable values of its coupling.
