Albert Barnes Commentary 2 Kings 3:19

"And ye shall smite every fortified city, and every choice city, and shall fell every good tree, and stop all fountains of water, and mar every good piece of land with stones." — 2 Kings 3:19 (ASV)

You shall fell every good tree - This is not an infringement of the rule laid down in Deuteronomy 20:19-20. The Israelites were not forbidden to fell fruit trees in an enemy’s country as a part of the ravage of war, when they had no intention of occupying the country. This method of injuring an enemy was probably in general use among the nations of that region at the time. We see this destruction frequently depicted on Assyrian monuments and mentioned in Egyptian inscriptions.

And stop all wells of water - The stopping of wells was a common feature of ancient, and especially Eastern, warfare .

Ruin ... with stones - This is the exact opposite of what is suggested in Isaiah 5:2. The land in and around Palestine is so stony that the first task of a farmer is to collect the surface stones into heaps. An army marching through a land could easily undo this work, dispersing the gathered stones and spreading them once more over the fields.