Would anyone can help identify what's attacking my citrus plant leafs and suggest some remedy for it? It's a 3-4 yrs Washington Navel Semi Dwarf planted in a 1/2 Whiskey barrel, it fruited excellent 4-5 oranges last year; but I am afraid I won't get any this season.
The close up first photo is the bottom, the 2nd is the top of the leaf.
The new young seemingly healthy leafs already sprouting in some places (3rd photo), so if I can prevent this from happening again, hopefully I will get better result next season.
As you can see I am a newbie in this forum as well as a home grower, so any help would be much appreciated!