Answer: Based on your description I suspect you are overwatering the fig. The soil should be allowed to dry out a bit between waterings. It should not be sopping wet or saturated, but also not bone dry. To know if you need to water, dig into the soil with your finger. Do not water until it is dry down and inch or two, but then water slowly and thorougly so it soaks down to the deepest roots. Use an organic mulch over the root area in a flat layer (do not pile it against the trunk) to help keep the soil shaded and moist between waterings.
The other possibility is a fungal infection. Since there are spots in addition to the yellowing, I would suggest you consult with your county extension to see if it might be that. If it is something that needs a chemical control, they will have the most up to date information on what to use and how/when is best to apply it for maximum results. In the meantime, clean up and dispose of any fallen leaves in the trash to limit sources of reinfection.
Good luck with your fig tree!
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