- Author: Ben Faber
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.
- Author: Neil O'Connell
European earwig
Wrap removed - whitewashed
Tree Wraps
Author - Neil O'Connell
Installing tree wraps on young trees provides protection to the trunk from applications of herbicides during weed management operations. Additionally, the wraps minimize light interception by trunk tissue thereby reducing sucker growth. During hot weather tree wraps provide shade to the trunk and reduce the incidence of sunburn. With the increasing incidence of earwigs, damage to young trees and the tendency for the insect to congregate under the wraps, tree wraps are being removed in some cases. Recent laboratory data from Dr. Beth Grafton-Cardwell (confirmed by observations in the field) suggests that as the season progresses adults become less and less interested in feeding on leaves (peak of feeding in March and April, declines to next to nothing by June). So, a management consideration would be to check the earwigs in the wraps in the summer, and if there are only adults present there is less concern than if there are immatures present. Another point would be to consider treatment with an insecticide such as Lorsban if wraps are to be left on for sunburn protection.
If wraps are removed a uniform coating of sun protective material should be applied to the trunk to protect against sun damage. Trunk surfaces should be monitored to ensure that a uniform coating is in place. Sun damage to unprotected trunk tissue can result in partial or complete girdling of the tree.
Tree Wrap article with pictures 7-6-12
- Author: Ben Faber, University of California Cooperative Extension
In both avocado and citrus there can be a rapid collapse of tissue brought on by a host of related fungi. The pathogen was once lumped as Dothiorella, but lately University of California extension plant pathologist Akif Eskalen has been able to tweeze out more species which mainly belong to the Botryosphaeria genus. The collapse can be quite rapid, so fast that the leaves continue to hang on to the tree. This disease is more common in years of low rainfall, where inadequate water is being applied (especially when Santa Ana winds are blowing), and where salinity build up has occurred. In the last 2 months, I have been called out to diagnose this problem five times. In each case, they were trees that had been sidelined and neglected or the grower was trying to save money by saving water. Luckily for a mature tree, there can be recovery as long the tree is protected from sunburn that occurs with defoliation. White wash the exposed parts, and wait for recovery. When it is clear what part is recovering, cut into fresh wood to remove the dead parts. For a more detailed discussion of this blight, see our 2009 Topics in Subtropics.
- Author: Ben Faber, University of California Cooperative Extension
In our latest edition of Topics in Subtropics - we printed an article by Tim Spann outlining some of the tactics being employed to deal with huanglongbing – “An Outline of Management Options for HLB in Florida”. Much of the presentation was on the use of nutritional sprays to mitigate the effects of the disease on fruit yield and quality. In the past, anecdotal evidence was used to evaluate the nutritional spray programs. Recently an article by Grottwald et. al., 2012 looked at nutritional sprays and found that even with the very expensive practice it was not possible to improve fruit size and tree yield with the sprays, even at a cost of approximately $750 per acre. This is the first trial to actually look at the impact of the sprays on yield. Tree canopies might look better, but effect on yield had never been fully evaluated. Further, by not following a rouging program of removing symptomatic trees, the spray program could promote area-wide buildup of inoculum and increase the spread of disease both within and between citrus orchards.
Gottwald, T.R., J.H. Graham, M.S. Irey, T.G. McCollum and B.W. Wood. 2012. Inconsequential effect of nutritional treatments on huanglongbing control, fruit quality, bacterial titer and disease progress. Crop Protection 36 (2012): 73-82
