FMV can really hurt a tree if the tree will struggle to live due to a bad climate.
Picture you with a lung disease. Hard for you to breathe. Your immune system works overtime to fix what is wrong, but then comes sticky heat and now you fight rust and nematodes. Then comes a freeze and now on top of all else, you have to fight freeze.
FMV in a Mediterranean Climate is easy. Nothing matters. The leaves look ugly. Period. BUT a FMV infected tree in a not so ideal climate could have a hard time surviving and producing the delicious figs of your dreams.
I actually cured FMV in one of my trees. I stuck it in a pot and it lived for 2 years with 2 leaves! I fried it's roots! If you put your trees in hot sun in a pot, you will cause serious stress and you will kill the virus, but you will see zero growth. When Jon rescued it for me by telling me to flood it with water followed by a dose of Miracle Grow, it took off like a rocket. That fig was Panachee from UC Davis. No signs of FMV. Beautiful tree.
It died, sadly. What eventually killed it? The dudes who sprayed the wrought iron fence didn't cover it, and the chemicals killed it. A member sent me another Panachee, and it is doing great in ground. It does have FMV, but no worries here. In it's place went Verte who is going to be 30' tall one day. It's on it's way. That fig has no visible FMV. Got it from Driveway Farmer.
Suzi