Reducibility of polynomials f(x,y)f(x,y) modulo pp

We consider absolutely irreducible polynomials $f \in Z[x,y]$ with $\deg_x(f)=m$, $\deg_y(f)=n$ and height $H$. We show that for any prime $p$ with $p>c_{mn} H^{2mn+n-1}$ the reduction $f \bmod p$ is also absolutely irreducible. Furthermore if the Bouniakowsky conjecture is true we show that there are infinitely many absolutely irreducible polynomials $f \in Z[x,y]$ which are reducible mod $p$ where $p$ is a prime with $p>H^{2m}$.Comment: Latex, 7 page