We received a query from Jill in Spain asking why her orange crop had all burst this season, rendering them pretty much inedible. And I can say we have similar problems here in Australia too, in fact all citrus except Grapefruit suffer from this problem from time to time – usually in autumn and most commonly Navel Oranges.
There are various reasons for it happening – all cultural, so all in your control.
#1. Too much water. This is the most obvious as too much content inside is bound to burst out at some point. The main time to keep watering to a minimum is in winter when the tree requires very little. Only ramp up the watering in spring and the heat of summer and make it a long, slow drink over the full root area – ensuring of course that the plant is in a perfectly drained location, preferably raised.
#2. Hot summer winds can also be a cause in that they dessicate (dry out) the rind and the fruit. The tree responds by taking on more water than usual to compensate, but as the rind has dried and thinned it cannot contain the new bulk of juice within and bursts open.
The best way to avoid this is to irrigate heavily when you know hot dry winds are due and then lightly, directly afterwards. This stops the plant having to relocate moisture from the fruit to the tree in emergency (to survive) thereby compromising the rind’s ability to stretch when new juice is created.
#3. Over fertilisation. Citrus are gross feeders, in particular needing a lot of nitrogen. Feed citrus regularly, once per quarter but make sure you don’t overdo quantities. If you do give them too much then they will take it all in regardless of needs, produce too much, too quickly and the end result is usually burst fruit.
The best way to avoid this problem is to apply sustained release fertiliser – though it is more expensive.
So there is no bug or disease that causes this problem and no chemicals to apply to solve it. Its all in your hands to observe the weather, maintain a good and consistent watering regime and fertilise steadily in correct amounts. Then you’ll enjoy the fruits of your labours.