The Battle for Alvega took place when the Daleks, having achieved space flight, created their fleet and tried to conquer Alvega, the planet closest to Skaro. When the native plant life, the Amarylls, retaliated, the Daleks engaged them in battle and almost lost.
First, the fires caused by the landing ships alerted the Amarylls to the Daleks' presence. Scout Daleks were sent out. They used fire-rays to clear a path when the Amarylls contacted their Controller deep in the core of the planet. Told to attack, the Amarylls blew seeds at the Daleks, which penetrated their casings, grew inside and strangled them from within.
One Amaryll was captured and studied by the Daleks. It told them they would never fall to the Daleks. Amarylls began to attack the Daleks ships when the Dalek Emperor ordered lift-off. As the main fleet continued on to other worlds, four ships stayed behind to scorch the planet. Most Amarylls were burned. Three ships landed to build a city and one searched the planet.
The Controller counterattacked with an Alvega Earthworm. It crushed the three landed ships. The Daleks in the fourth ship devised a plan to attack the Controller. The ship burrowed into the ground with excavation drills until it was attacked by the worm. The ship was crushed and the Daleks, having killed the worm, were trapped underground.
They made their way to the core, buried and crushed by falling debris, until only one Dalek remained to attack the Controller and destroy it. This made the planet explode. The Emperor, observing this from the fleet, decreed that whatever the Daleks could not conquer, they would destroy. (COMIC: The Amaryll Challenge)