The radical of the bidual of a Beurling algebra

We prove that the bidual of a Beurling algebra on $\mathbb{Z}$, considered as a Banach algebra with the first Arens product, can never be semisimple. We then show that $rad(\ell^1(\oplus_{i=1}^{\infty} \mathbb{Z})")$ contains nilpotent elements of every index. Each of these results settles a question of Dales and Lau. Finally we show that there exists a weight ω on $\mathbb{Z}$ such that the bidual of $\ell^{1}(\mathbb{Z}, \omega)$ contains a radical element which is not nilpotent.