Since there are so many Nurgle releases, including even a special tree, we've found some examples of how you can make infested and rotten terrain yourself.
In fact, the main thing here is not to make it too much spoiled - the early stage of corruption looks the most horrific since you can see from where it started.
However, it's ok to mix it with the whole lakes of rotten flesh. You can use silicone or water imitation for them. Luckily Citadel has the huge amount of special paints to make them look disgusting.
The corrosion from this knight's legs can be also made on the destroyed vehicles on the battlefield. All you need is some green stuff.
Such terrain pieces with blisters can be scattered all over the battlefield since they are easy to make and can create a specific atmosphere. Also, take a look at the paints - you can use the same ones when painting such elements on infantry models.
And green stuff will help you to "infest" almost any piece of terrain. Hope, you don't have tripophobia...
ANnd the works below are pieces of art themselves and really hard to make. Don't be afraid to try and use your imagination! Where else, if not with the daemonic terrain?