Blocking sets in desarguesian projective planes

Using theorems of Redei, and of Brouwer and Schrijver, and Jamison, it is proved that a non-trivial blocking set in a desarguesian projective plane of order q has at least q + v(2q) + 1 points, if q is at least 7, odd and not a square and q ¦ 27. Further one can show that non-trivial blocking sets in the desarguesian planes PG(2, 11) and PG(2, 13) have at least 18 resp. 21 points, and this is best possible. In addition a nice description of a blocking set of size qt + qt-1 in the desarguesian plane PG(2, qt) is given, where q is some prime power.