Is this due to papaya lethal yellowing virus, excess watering or over-fertilization?

How does the new growth look? From the photo it seems healthy.

Papayas are not 'evergreen', lower leaves die off as new ones grow in at the top to replace them.

There is no new growth & the fruit has stopped growing. The plant is only 5.5 months old and has lost all the lower leaves - about 18 of them. It is dying.

Did you have all of those Florida rains...... I had problems with flooding just a couple of weeks ago.... and even where it did not flood, the ground was squishy.... I had 14 inches in one day and night.... and it rained for several days.....

I see what looks like new growth in the photo, and leaves appear healthy. Can you take a closer pic?

And papayas take a very long time to ripen, once they reach full size. They really do not look diseased in your photo, but as I stated, it's somewhat hard to tell from that distance.

Here are some pages with papaya info, if you haven't seen them already:

https://floridata.com/plant/902

https://edis.ifas.ufl.edu/mg054

I grew a few from Seeds in Florida. They grew like weeds. I never fertilized and I don't think I even watered them. We don't have a sprinkler system.

I got loads of delicious fruit. Mine were all female but my neighbor had a male plant. Those were the best trees and the fruit was fantastic. We got so many, I gave bags away.

When Irma hit Sarasota, they all blew over. They are very shallow rooted and the wind and rain blew them over.

Mine were grown from seed from Papaya's bought in the supermarket.

Jane

Water and fertilizer affect whole tree, all leaves.

Our papayas up here in 9a are starting to lose leaves just like everything else. They'll probably get frozen back during the winter anyway, if we have a big freeze. I'm actually going to be taking all of mine out.