We discuss the possible phenomenology of the additional charge ( − 1 3 ) colour triplet particles D 1 2 of spin 1 2 and D 0, D 0 c of spin 0 which are contained in each matter generation if the superstring is compactified on a Calabi-Yau manifold. In the minimal model with no intermediate mass scales and supersymmetry breaking fed into the observable sector via a gaugino mass, either a spin- 1 2 or a spin-0 D particle could be the lightest, and either could be as light as the present lower bound from e +e − experiments of about 20 GeV. The D particles could behave as leptoquarks coupling to quarks and leptons, in which case the single production process ep → D 0( D 0 c ) + X would occur, and D 0( D 0 c ) → l q, D 1 2 → l q χ decays would dominate, where χ is the lightest supersymmetric particle. Alternatively, the D particles could behave as disquarks coupling ( p ) p → D 0( D 0( D c , D 0 D 0 c ) + K to pairs of antiquarks, in which case the single production process would occur, and D 0( D 0 c ) → qq , D 0 c ( D 0) → qq , D 1 2 → qq χ decays would dominate. We present cross sections for ep → D 0(D 0 c + X, ep → D 0( D 0 c ) + X, ( p ) p → D 0( D 0 c , D 0 c , D 0 c , D 0) + X, e + e − → D 0 D 0( D 0 c D 0 c ) and D 1 2 D 1 2 , ( p ) p → D 0 D 0( D 0 c D 0 c and D 1 2 D 1 2 + X . We calculate the experimental signals and estimate backgrounds for D production and decay in these processes. The decays D 0( D 0 c ) → l q and D 1 2 → l q χ or qq χ would be detectable in most of these reactions, but D 0( D 0 c → qq decays may only be detectable in e + e − → D 0 D 0( D 0 c D 0 c ) collisions.