I've had this potted Meyer lemon for years, which I put outdoors during May - October generally and it's indoors in winter. Last year it grew lush new growth and produced about 12 large lemons. This year, it's showed almost no growth, leaves look bad, and now in the past three or four days, some of the leaves have large rusty brown areas along the edges. They're not spots all over the leaves, just starting from the edges. There is also some yellowing. I feed and water it regularly and add some iron, just as I have been doing for years. It's in the same spot on the patio as always. I don't see any insects on it. Although it has a few scale insects indoors, I always pick them off and they never reappear while the plant is outdoors all during the warm weather. Any ideas are welcome.