Best to just use one dyson to explore, since there are plenty around. Find the uncolonized, then send over a bucket-load (without hitting the defense planets) to grow 5 dyson trees. You won't need to plant defense trees at all on this map. Once you find your hidden seedlings on the other side of the map, you can use them to grow 5 dyson trees and replicate quickly. Then take out the satellite asteroids (that have defense trees all over), keep moving your dyson all onto one location to gather an army (speedy ones here are actually really good against the defense drones en masse of about... 70), then take out the planet that's holding the actual enemies.
I think there may be a long time delay before the enemy starts sending their seeds to attack your base, so conquer the satellites for safety first. Sure it takes a while but if you know how to "collect" a large amount of seeds, it'll be a cakewalk. That means planting all the dyson trees at one time for faster replication results, and a defense tree either before them or after.