I don't think you should fertilize; it will just stress the tree more. If it is newly planted, perhaps you could lift it higher. A lot of our things are suffering with too much water.
I lost a purple plum tree the year that Hurricane Lili and that Tropical Storm before her came through here. Too much water in too short a time.
I would try elevating the tree.

Excellent advise. We used to have a plum that did very well until we had an extra wet summer and it croaked. It might be worth it to build up a berm for such things. Sometimes you'll read you should build a raised bed, but too often the timbers or whatever you use to edge it hold in the water and what you create is a giant bathtub. Drainage is really a problem in years like this.

I planted a small plum tree last summer. It made it through the winter fine but this summer the leaves are curling up as if it gets no water. In other words, they are dry and crispy and shot thru with holes. We are in a semi drought here in south Georgis so I water every few days. I see no insects other than a friendly yellow spider. I am to the point of digging it up and potting for a year. Now the leaves are starting to go limp and drop off. Help!