I mulch my citrus and let weeds grow under them. I try to keep the weeds cut back but sometimes I get lazy.
I get tons of fruit also. All my citrus is healthy and in heavy bloom currently.
I don't have a sprinkler system and never water my trees (unless newly planted).
I think you get into problems when the roots stay moist 24/7, but I don't have that problem since I never water.
For commercial growers, yes never mulch. They typically have water fed to the trees anyway. Homeowners, I would say yes, mulch.
Once trees can shade their own roots then mulching is probably less important. But for young citrus I say mulch. The benefits outweigh the cons in my opinion. Mulch out past the drip line on a young citrus will allow adventurous roots to go there. No expert on nematodes but I think the mulch helps lower their numbers.
Also, yes, good advice to keep weeds away also. But, not 100 percent necessary. One thing to avoid, and is common sense, is to keep grass from growing up the trunk. Weed Wacker newbees like to cut the trunk with the grass.
