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Standing water can lead to asphyxiation
ASPHYXIATION
Asphyxiation is a physiological problem that may affect certain branches, whole limbs or the entire tree. Leaves wilt and may fall, the fruit withers and drops and the branches die back to a greater or lesser extent. The condition develops so rapidly that it may be regarded as a form of collapse. Usually, the larger stems and branches remain alive, and after a time, vigorous new growth is put out so that the tree tends to recover.
Asphyxiation is related to the air and water conditions of the soil. The trouble appears mainly in fine-textured or shallow soils with impervious sub-soils. In 1997-98, this even occurred on slopes with normally good drainage because the rains were so frequent. When such soils are over-irrigated or wetted by rains, the water displaces the soil oxygen. The smaller roots die when deprived of oxygen. When the stress of water shortage develops, the impaired roots are unable to supply water to the leaves rapidly enough and the tree collapses. The condition is accentuated when rainy weather is followed by winds or warm conditions.
Canopy treatment in less severe instances consists of cutting back the dead branches to live wood. If leaf drop has been excessive, the tree should be whitewashed to prevent sunburn. Fruit, if mature should be harvested as soon as possible to prevent loss. In the case of young trees, less than two years of age, recovery sometimes does not occur, and replanting should be considered if vigorous regrowth does not occur by July.
Asphyxiation can be reduced by proper planting and grading. If an impervious layer is identified, it should be ripped prior to planting. The field should be graded so that water has somewhere to run off the field during high rainfall years. Heavier soils might require planting on berms or mounds so that the crown roots have a better chance of being aerated.
Post-plant, if an impervious layer can be identified and is shallow enough to break through, ripping along side the tree of drilling 4-6 inch post holes at the corners of the tree can improve drainage. It is important that the ripper blade or auger gets below the impervious layer for this technique to be effective.
