Can anyone shed light on why approx one in three of my 3to 4 yr old Kalamata trees start to get very pale older leaves which eventually drop off and the whole limb defoliates.No other signs off distress.Have cut trees back hard and they reshoot-still early days,don't know if they will do the same thing down the track.Trees were purchased from Olea nusery-don't know what they were grafted on to.Have many other varieties,none of which exhibit this problem.Am getting very frustrated as they(kalamatas) grow well then go downhill.hope someone can help.Thanks.