Hi,
That girdle, it looks like a wire from the fence (or a dog chain) was running around the tree. Trees usually recover from that. I would perhaps stake the top growth.
As it is wind may take that top growth down from the weight of the leaves and fruits.
I only weed mechanically next to my trees . With chemicals you may lose control and lose the tree. So just keep on cutting the root-shoots and cuttings the weeds.
After a while the tree will shade its feet and the weeds will slow down.
You could use coper-fungicide on the trunk,stems and leaves.
You could white wash the trunk with lime. Usually those fungal diseases are helped in spreading by crawling insects like ants and caterpillars ( wind too, but...).
The white wash/lime will take a toll on those insects and you'll get less problems on the leaves.
You should clean the base of the tree for overwintering insects will rest there. Pour some lime next to the tree on a 10cm/3'' circle around the tree.
Keep the trunk white on a 10cm/3'' ring . Apply again in March next year and keep the lime barrier up and running through out the growing season.
I always had problems with fig moths (caterpillars netting and feeding on the fig leaves) and so far got rid of them with the lime after applying lime this last July.
By the way, now, that is one of a trunk especially for a fig tree.