The Stillbark Blight

A blight climbs the Stillbark orchard. The grovekeeper wants it stopped before the canopy.

Requirements

Speak with the grovekeeper at Stillbark Bank
He sets a blackened branch on the counter. The bark sloughs off in your hand. 'Three south rows already. If it reaches the canopy I lose the orchard. Walk it with me.'
Walk the blighted rows
The blight runs in straight lines, not in patches. Whatever's spreading it has a path, not a wind. The grovekeeper marks the worst trees with chalk as you go.
Check the irrigation cut at the sea
The irrigation channel from the sea has stained banks. The blight is in the water, not the trees. Something upstream is bleeding into the channel.
Set a cleansing sigil at the obelisk
The obelisk holds the cleansing pattern long enough for you to seat it into a chain of channel stones. The next pull from the sea runs clear by morning.
Treat the marked trees
You cut back the worst three rows to clean wood and burn the trimmings on the headland. The grovekeeper salts the stumps. By evening the chalk marks come off easily.
Hunt for the source in Pinewrap wilds
Two miles upstream, you find a sluiced patch where someone has been dumping spoiled fertilizer into a feeder creek. The dump is fresh. The cans are stacked, not scattered.
Report the dump site to the grovekeeper
He goes still. 'Stacked, not dumped. Someone meant my orchard. I'll find out who. You saved the canopy. Take the orchard's thanks in produce.'