When considering how to manage and prevent wood rot disease in lemons, a grower should consider both the short- and long-term steps. The first of the short-term steps is to prune out diseased wood. This step is critical, and should occur as soon as the damage is noticed, particularly following wind storms, hurricanes or freeze damage. Since the wood rot fungi thrive and grow when temperatures are high, damaged branches may be easily noticed during the late summer and fall.

Prune the branch back to a point where there is no longer evidence of the disease on the cut surface of the limb. Saw blades should be sharp so as to produce a smooth cut. Jagged cuts will provide sites for re-infestation of clean wood. Diseased wood should be removed from the grove as soon as possible.

Trees should also be topped, hedged or hand-pruned to remove "whips". Whips are those long, vigorous, upright branches that extend above the canopy and often have fruit growing at their tips. These should be removed before the weight of the fruit causes the branches to break. Pruning should also remove branches that extend into the middles, and branches that have been damaged due to heavy fruit load. Annual pruning operations should be scheduled for late winter, before temperatures get high and the wood rot fungi become active. Again, saw blades should be sharp.

Long-term management steps should include a commitment to avoid damage to groves from implements such as tractors, forklifts, and sprayers. Properly hedged groves will not have branches that extend into the middles that would catch on implements. Drivers of farm tractors should be educated to avoid damaging the trees.

Also, it is important to avoid damage to the tree from picking ladders. Ladders should be placed gently against the trees to avoid damage. Also, ladders should not be left against the trees overnight, as they can add additional weight to fruit laden branches, particularly if it is windy. When tree damage does occur due to these causes, grove managers should be notified so that the broken limbs can be removed.

Finally, new plantings should be planned to avoid limb breakage. Spacing of less than 22 ft between tree rows should be avoided, since close row-to-row spacing will invariably lead to damage when implements are driven down the row. If higher tree densities are desired, consider planting in the hedge-row design, double hedgerow design, or in the diamond design in which trees can be removed when crowding will lead to limb damage.

Extensive wood rot is not a foregone conclusion in any Arizona lemon grove. With diligent management, the onset of the disease can be delayed and productivity maintained.

More information on lemon diseases

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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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