Aphids and Leaf Curl

I have a very sick little loquat tree. I noticed some of the leaves curled and covered with aphids recently and I didn't do anything. I just passed by it today  again and it's loaded with aphids and ants and the leaves that are most loaded with aphids are completely curled in and turning black. I tried hosing underneath the leaves with my hose but the leaves are so curled so it's really tough to get them all out from under the cracks and crevices. What should I do? Would it be better to remove all the leaves that are really infested and turning black?  I've got a thick layer of grass clippings and leaves around the base of the tree, what else can I do to boost the tree's immunity and prevent this from happening again?

The black leaves are a classic sign of the presence of aphids. I believe it is reference to as sooty mold? Ants will 'farm' the aphids for their honeydew which you probably will not appreciate.

If you don't mind semi-frequently taking a peek, spraying the aphids/ants off could be enough to take care of your issues. Perhaps look into encouraging predatory insects through habitat like lacecwings to take care of future aphid issues for you.

If it's not going to kill the tree, I usually leave aphids and next year have an excess of birds that like eating aphids.

As for ants. These are the bigger problem as they bring aphids and some types help curl the leaves to protect them.  Ants are such annoying farmers.   I might put sticky stuff around the trunks of the trees to reduce the ant access.

No, do nothing, aphids are good food for predator insects. They will come, i've observed waves of lady bugs, parasitic wasps other bugs and more waves on the peach trees. Plant more diversity in the garden and they'll find refuge closeby and be on top coming years, making an outbreak less likely. You could see it as investment against future outbreaks.

Are plums or other stone fruits found in your area?  May be worth checking for viruses since loquat is a close enough relative to other stone fruits and is known to become infected by plum pox virus, a virus transmitted by aphids and well known in southern Europe..  If you have knowledge of either a university or agricultural assistance office in your area, they may be helpful with a diagnosis of the disease in addition to, or beyond, the damage cause by the aphids alone.