I have a fan palm that's stricken with fungus, as in the pic. I live in Las Vegas (desert) and have a drip irrigation system. Thus far, I applied two weekly treatments of a spray fungicide. One nursery suggested Jack's Copper Fungicide and said that I should water only once a day, in the morning, for about 30 minutes. I've been watering twice a day. I don't know how long I should continuing applying the fungicide, so will it eventually eliminate the fungus. Any advice will be appreciated.