  Let $k$ be a field of positive characteristic. Building on the work of the
second named author, we define a new class of $k$-algebras, called diagonally
$F$-regular algebras, for which the so-called Uniform Symbolic Topology
Property (USTP) holds effectively. We show that this class contains all
essentially smooth $k$-algebras. We also show that this class contains certain
singular algebras, such as the affine cone over $\mathbb{P}^r_{k} \times
\mathbb{P}^s_{k}$, when $k$ is perfect. By reduction to positive
characteristic, it follows that USTP holds effectively for the affine cone over
$\mathbb{P}^r_{\mathbb{C}} \times \mathbb{P}^s_{\mathbb{C}}$ and more generally
for complex varieties of diagonal $F$-regular type.
