Wellington, New Zealand

When is the best time to spray a lemon bush with copper to prevent brown spots appearing on the lemons? The bush has been very productive and the lemons are fine, but the skin has been quite badly marked with brown patches although this doesn't seem to have any effect on the taste. As I have only recently emigrated to New Zealand I have not had previous experience of growing lemons but have been advised to spray the bush with a copper substance and would like to know what time of year is best to do this.

• 4 May, 2009