Arboriculture & Urban Forestry 33(3): May 2007 Arboriculture & Urban Forestry 2007. 33(3):185–192. 185 The Influence of Commercial Film-Forming Polymers on Reducing Salt Spray Injury in Evergreen Oak (Quercus ilex L.) and Laurel (Prunus laurocerasus L.) Glynn C. Percival and Gillian A. Fraser Abstract. A field trial was undertaken to determine the influence of four commercially available film-forming polymers (Bond [alkyl phenyl hydroxyl polyoxyethylene], Newman Crop Spray 11E™ [paraffinic oil], Nu-Film P [poly-1-p men- thene], and Spray Gard [di-1-p menthene]) on reducing salt spray injury on two woody species, evergreen oak (Quercus ilex L.) and laurel (Prunus laurocerasus L.). Irrespective of species, the film-forming polymers Nu-Film-P and Spay Gard did not provide any significant degree of protection against salt spray damage irrespective of concentration (1% or 2%) applied as measured by leaf chlorophyll concentrations, photosynthetic efficiency, visual leaf necrosis, foliar sodium and chloride content, and growth (height, leaf area). The film-forming polymer Newman Crop Spray 11E™ provided only 1-week protection against salt spray injury. The film-forming polymer Bond provided a significant (P < 0.05) degree of protection against salt spray injury 3 months after application as manifest by higher leaf chlorophyll content, photosynthetic efficiency, height and leaf area, and lower visual leaf necrosis and foliar Na and Cl content compared with nontreated controls. In conclusion, results indicate that application of a suitable film-forming polymer can provide a significant degree of protection of up to 3 months against salt spray injury in evergreen oak and laurel. Results also indicate that when applied at 1% or 2% solutions, no problems associated with phytotoxicity and rapid degradation on the leaf surface exist. Key Words. Antitranspirants; carotenoids; chlorophyll fluorescence; chlorophylls; English oak; laurel; leaf necrosis; photosystem II; sodium chloride; urban trees. Deicing salts in the form of sodium chloride (NaCl) are used widely throughout the United Kingdom to maintain roads free from ice and snow to ensure public safety (Ryan 2005; Zim- merman and Jull 2006). However, NaCl can be a major chemical pollutant in urban landscapes having a detrimental effect on roadside vegetation (Percival et al. 2003). Salt dam- age occurs by direct toxicity of the chloride ion resulting in a reduction in leaf chlorophyll concentration and concomitant photosynthetic performance, breakdown of leaf structure at the cellular level, necrosis, bud failure, and twig and branch dieback (Zhu 2001). Sodium tends to damage soil structure by competition with other cation exchange sites causing nu- trient deficiency symptoms and increased soil pH (Gibbs and Palmer 1994). Deicing salts are estimated to be directly re- sponsible for the deaths of >700,000 trees annually in West- ern Europe alone (Dobson 1991) and are particularly devas- tating to young spring growth that is unable to acclimate and therefore extremely susceptible. With increases in traffic vol- ume and the expansion of road networks throughout the United Kingdom, the quantity of salt used for deicing opera- tions has increased correspondingly. Consequently, there is a demand for salt-protectant compounds that are inexpensive, can be applied at relatively short notice, and require only small adjustments to existing management aftercare proce- dures (Percival and Barnes 2005). Film-forming polymers and spray oils are widely used as spray adjuvants and antitranspirants within the agricultural and horticultural industries. When applied, they form a physi- cal barrier across the leaf or twig surface and concomitantly form an insulating layer between the leaf/twig surface and atmosphere (Fuller et al. 2003). Such effects may protect against direct salt damage caused by coastal spray, rain, and/ or traffic splash of water contaminated with deicing salt. When tested by a number of researchers in the 1970s, most concluded that antitranspirant and antidessication-based film- forming polymers did not offer promise as a feasible salt amelioration technique either proving to be ineffective or directly phytotoxic to leaf tissue (Constantini and Rich 1973; Emmons et al. 1976; Sauer 1980). Developments in polymer technology, however, have led to the formulation of a range of new polymers that contain different active ingredients from the original products used in the earlier trials that are ©2007 International Society of Arboriculture
May 2007
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