Wood products for exterior residential applications have long been protected with metallic preservatives. However, environmental and disposal concerns and governmental regulations have resulted in a growing trend to employ organic systems based on relatively benign and expensive agrochemicals. To develop organic preservatives that have increased efficacy and lower cost, various groups are studying the biocidal and non-biocidal properties of extractives present in naturally durable heartwoods. In this study, we determined the fungicidal, free radical scavenger/antioxidant, metal chelation and Fe3+ reducing properties of some flavones and flavonoid analogs and chromones. The results support our earlier hypothesis that the abiotic antioxidant, Fe3+ reduction and subsequent metal complexation properties, in combination with the extractives’ fungicidal properties, all have a role in natural durability. Consequently, it may be possible to employ non-biocidal additive(s) with the above abiotic properties to enhance the efficacy of the relatively expensive organic agrochemicals used to protect wood.

We previously found that a combination of various organic biocides with low-cost non-biocidal antioxidants gave enhanced (synergistic) efficacy against wood-decaying fungi. The best laboratory results were obtained with propyl gallate, perhaps due to its dual antioxidant/metalchelating properties. In this study we report on potentiometric titration experiments for the complexation of Fe2+ with propyl gallate. The results suggest four coordination compounds are present in the pH range from 3 to 12. These are [(H2PG)Fe]+, (HPG)Fe, [(PG)Fe]−, and [(HPG)2Fe]2− {PG=O3C6H2CO2CH2CH2CH33−}. Equilibrium constants for the formation of all complexes are given. A plot of species present versus pH clearly indicates that propyl gallate strongly complexes with Fe2+ at the mildly acidic pH levels normally present in wood, with some complexing still possible in relatively acidic environments present in decaying wood. Propyl gallate complexes more strongly than catechol at the pH values of normal wood. Propyl gallate may also interfere with the proposed fungal redox cycles. Metal complexation may thus be an important part in the overall mechanism by which propyl gallate and organic biocides synergistically protect wood. Furthermore, the metal chelating properties of heartwood extractives, such as the hydrolysable tannins from which propyl gallate is made, may be an important factor in natural durability.

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Discoloration of bermudagrass often results from application of MSMA herbicide used to control southern crabgrass and other weeds. However, when products containing iron sulfate (FeSO4) are tank-mixed with MSMA, this discoloration is reduced. Experiments investigated the effect of tank-mixing organic arsenical herbicides with FeSO4or a chelated iron source (Sprint 330) in terms of southern crabgrass control and injury to bermudagrass. Tank-mixing MSMA with FeSO4reduced bermudagrass injury. However, southern crabgrass control was also reduced by at least 50% with the addition of ≥0.38 kg Fe2+ha−1. Neither antagonism nor safening of bermudagrass was observed when the chelated Fe2+source was used. Applying FeSO4as a separate treatment 1 to 4 d before or after MSMA application did not reduce visual burmudagrass injury 1 wk after treatment. Solution pH and FeSO4concentration controlled the extent of complexation and level of antagonism observed in the field; inorganic Fe2+reacted with MSMA to form a complex having reduced herbicidal activity. Potentiometric and spectrophotometric investigations found that methylarsonate, the parent acid of MSMA and other organic arsenical herbicides, reacts with inorganic Fe2+to form a stable 1:1 Fe2+-methylarsonic acid chelate having two points of metal coordination and a stability constant log10(β) = 2.77 ± 0.04. Tank-mixing MSMA with FeSO4to protect against bermudagrass injury negates the benefit of applying the herbicide for weed control, and therefore is not a recommendable practice for turf managers.

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