I've seen this before on plants suffering from prolonged periods of wet & cold weather - making them susceptible to various other scourges. Lemons need at least 8 hours of unobstructed direct sun per day - as they have in Florida. That alone would eliminate many problems.

I don't know what that is, but it isn't a leaf cutter bee! They take nearly perfect circular "bites" out of the edges of the leaves. This lookes like some kind of caterpillar damage, plus a fungal leaf spot.

Thank you both. I didn't put a picture of the bee damage, as you say they are clean bits. I think you may be right Bathgate, we did have a couple of weeks of very wet and windy weather. Have now cut of the nasty bits, given it a feed and tucked it up in the greenhouse for the winter. I'm off to Florida!

Not Arizona? :D

I've never been there, is it good? My sister has a second home in Fort Myers so am going there for 3 weeks. Gardening is a bit different there!

Bit different here, too! Southern Arizona in winter is usually sunnier than Fort Myers, Florida, a bit warmer in the day, and a bit colder at night, and with lower humidity. That goes for Yuma, Ajo, and the Phoenix Metropolitan Area, where I live, while Tucson is usually around 10º F colder (but still beautiful). You can swim, as long as the pool is heated, and you can ski by driving into the nearby mountains--less than 2 hrs. drive time.

I went to a conference last November in Scottsdale next to Camelback. It was very arid but had a rugged beauty that was hard to ignore with the red rock formations and saguaro cacti in bloom. There's no place like it.