  We investigate diagonal forms of degree $d$ over the function field $F$ of a
smooth projective $p$-adic curve: if a form is isotropic over the completion of
$F$ with respect to each discrete valuation of $F$, then it is isotropic over
certain fields $F_U$, $F_P$ and $F_p$. These fields appear naturally when
applying the methodology of patching; $F$ is the inverse limit of the finite
inverse system of fields $\{F_U,F_P,F_p\}$. Our observations complement some
known bounds on the higher $u$-invariant of diagonal forms of degree $d$. We
only consider diagonal forms of degree $d$ over fields of characteristic not
dividing $d!$.
