Seeder ships are more susceptible not to explosives, nuclear weapons, dark energy, and yes, even magic. Armor piercing, incendiary, shockwave, pulse, laser, they won't do much.

If you want to use your supermagics, go ahead. Sure, it'll be better than energy or special munition weapons, but it really won't make a difference, unless you have a fleet firing on it. And these ships are big, as well as their pilots, so remember that too.

Now what have I left?

Also, you might want to forget your troubles on the ground and get off the planet. There's about a 5 hour period from the seed-drop to the mine-laying. Anything bigger than unusually small drop pods will get toasted in that field.

And if you stop traffic, and use a bunch of random jumps, that'll delay Seeder Ship spread. Otherwise, your empire is like a web. The more spider-silk intersections it captures, the more it can attack simultaneously.