Wikia

Desecration
Your Plague, Scourge, and Necrotic Strikes defile the ground within 7 yards of your target. Enemies in the area are slowed by X% while standing on the unholy ground. Does not trigger against targets that are immune to movement-slowing effects. Lasts 20 sec.
Usable by
Class	Death knight
Properties
Location	Unholy Tree, Tier 2
Affects	N/A
Ranks	2
Requirements
Points required	5
Spec specific	Yes
Talent required	None
Related debuff
Desecration Standing upon unholy ground. Movement speed is reduced by X%.

Desecration is a talent in the Unholy Tree, you will need to spend 7 points in Unholy to max it.

Rank table

Rank	Movement speed reduction
1	25%
2	50%

Patch 4.1.0 (26-Apr-2011): No longer triggers when an applicable strike hits a snare-immune target. This is primarily to avoid unnecessary spell effect clutter during boss encounters.
Patch 4.0.6 (8-Feb-2011): Desecration is now also triggered by Necrotic Strike
Patch 3.3.0 (08-Dec-2009): The debuff from this ability will no longer sometimes appear as if it were cast by someone else. In addition, the visual and snare from this ability will now both dissipate at the same time. Further, this talent will now respect snare immunities, and no longer sometimes snare immune targets. Duration increased to 20 seconds from 12.
Patch 3.2.0 (04-Aug-2009): This talent has been reduced to 2 points for 25/50% snare and no longer increases damage done by the death knight. It has also been moved one tier earlier in the tree and its spell effect has been made more transparent.
- No longer causes unnecessary combat logging.
Patch 3.1.0 (14-Apr-2009): This talent now has a 100% chance to be triggered. Additional points in the talent increase the damage bonus and snare magnitude instead of increasing the chance.
Patch 3.0.8 (2009-01-20): Will no longer break stealth.