Q. Some of the fruit on my navel orange tree splits before it ripens. What’s happening?
Nell P., San Luis Obispo
A. Most likely, pressure inside the orange increased more than the rind can handle, so the rind bursts like an over-inflated tire. And that was caused because the tree itself is stressed.
It usually occurs in green fruit between September and November.
Drought-stressed navel oranges are affected, other orange varieties not so much. This may be because the split usually starts at the navel end, the thinnest part of the rind. The split can be short and shallow, or deep and wide. Fortunately, it is not caused by pests or diseases.
Fruit split is likely the result of stress to the tree — caused by such factors as extreme temperature changes, wind, humidity, insufficient soil moisture and potassium deficiencies.
Hot weather, especially with winds, causes the tree to take water from young fruit, softening it. If the tree is then irrigated heavily, the dehydrated fruit swells, causing the rind to split. Most susceptible are young or dwarf varieties with small, shallow root systems, or trees grown in sandy soils that don’t retain sufficient moisture.
You can help prevent this by controlling irrigation and fertilizer applications.
Consider the age of the tree and the weather when deciding how much and how often to water. Younger trees need to be irrigated more frequently because their developing root systems dry out more quickly than older trees. Check the moisture of the soil below one inch to decide if the tree needs water. Follow the weather forecast and prepare to irrigate before hot windy days, then irrigate lightly for a few days if needed. Water a large area of soil around the tree but keep the base of the tree trunk dry.
If trees are fertilized, water first, apply according to the label instructions and water afterwards. Do not over-fertilize. Consider smaller monthly applications of quick-release fertilizer from February through May instead of a single large application. Time-release fertilizers conveniently supply nutrients at an even rate throughout the growing season.
Remove and discard damaged fruit to prevent unwanted insects and the spread of bacteria and fungi.
For more information go to: http://ucanr.edu/repository/a/?get=54110
Polly Nelson is a UCCE master gardener.
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