Dragonsdawn (1988)

The beautiful planet Pern seemed a paradise to its new colonists - until an unimaginable terror turned it into hell.
Suddenly deadly spores were falling like silver threads from the sky, devouring everything - and everyone - in their path. It began to look as if the colony, cut off from Earth and lacking the resources to combat the menace, was doomed.

Tehn some of the colonists noticed that the small, dragon-like lizards that inhabited their new world were joining the fight against Thread, breathing fire on it and teleporting to safety.
If only, they thought, the dragonets were big enough for a human to ride and intelligent enough to work as a team with the rider ...

And so they set their most talented geneticist to work to create the creatures Pern so desperately needed - Dragons!

FIRST THREADFALL!

Sorka glanced over her shoulder, and terror lent strength to her arms as she urged the mare to greater effort. They were nearly to the ledge, nearly to what little safety it offered from the hissing silver fall that splatted so ominously across the woods they had only just left.

On the shoreline, the thick clumps of tough bushes they had ridden through only moments before were no longer visible, covered by a writhing mass of "things" that seemed to enlarge as they watched. 

Sorka felt sick to her stomach.