Guild Wars 2

Tempest Defense grants increased damage (20%) to Stunned or Knocked-Down foes (works with Daze too, but not on tooltip).

1.There might be some issues. Warhorn has no source of Stuns or Knock-Down. In fact, it only has Pull or Knockback. As a result, these sources of damaging CCs do not benefit from this trait; nor does Lightning Rod on their case. Earth Shield pull

2.Additionnally, Lightning Rod damage is not increased when target is knocked-downed by Unsteady Ground (Earth 4).

3. Dazes from Air Leap Finishers do not apply the damage increase on the ability doing the Leap (lightning hammer 2, Flame Axe 5), but it does increase the damage on Lightning Rod.

So, to conclude.

Tempest Defense does increase damage of Lighting Rod (nor does it increase the damage of the ability causing the disable) when procced fromn the following spells : Gust, Unsteady Ground, Magnetic Shield, Updraft, Tidal Surge, Cyclone, Tornado…