Petroleum-derived spray oils, commonly referred to as horticultural spray oils, have been used to control insect and fungal pests in horticultural crops since the 1800s (Agnello, 2002). There has been renewed interest in PDSO because these products, when properly refined, have minimal human toxicity and environmental impact (Ebbon, 2002). Although there is debate as to how PDSOs affect plant pests, they can be lethal to plant pests and have the potential to stimulate innate plant defenses (Cortes-Barco et al., 2010a; Northover and Timmer, 2002; Traverner, 2002).
Civitas™ (Suncor Energy, Mississauga, Ontario, Canada) is a novel PDSO that contains a mixture of food-grade isoparaffins (alkanes) ranging in size from 16 to 33 carbons in length and an emulsifier (Hsiang et al., 2013). It is currently produced and marketed by Petro-Canada for disease and insect control in golf turf management. Civitas represents a novel approach to turf pest management because it primes plant defense yet has no fungicidal and limited fungistatic properties (Cortes-Barco et al., 2010a). Specifically, Cortes-Barco et al. (2010a, 2010b) demonstrated that Civitas primed or activated genes involved in induced systemic resistance, including genes involved in the jasmonic acid pathway when applied to both Nicotiana bethamiana and creeping bentgrass (Agrostis stolonifera L.). Consequently, several studies have shown reduced pesticide requirements when using Civitas in a disease management program (Aynardi et al., 2011; Aynardi and Uddin, 2013a, 2013b; McCall and Focht, 2010; Popko et al., 2010; Popko and Jung, 2013).
Acute and chronic phytotoxicity is a known limitation of PDSOs (Hodgkinson et al., 2002). Acute phytotoxicity results from direct damage to plant tissue including leaf lesions, fruit sunburn, and cell membrane disruption (Hodgkinson et al., 2002). Chronic phytotoxicity arises from inhibition of stomatal conductance (gS) causing reductions in transpiration, photosynthesis, and respiration and an increase in photorespiration, photo-oxidation, and oxidative stress (Hodgkinson et al., 2002). For example, a paraffinic PDSO was shown to reduce gS in grapes and altered carbon partitioning (Finger et al., 2002). Similar results have been demonstrated in other horticultural crops (Rethwisch et al., 1992).
Most modern PDSOs are highly paraffinic and are considered safe when mixed with water at concentrations less than 2% by weight (Beattie, 1990). Currently, Civitas is applied at 2.5% to 5% concentrations and can result in turf chlorosis within hours of application. To mask the chlorosis, Civitas is applied with Harmonizer™ (Suncor Energy), which is a green phthalocyanine pigment (Nash, 2011). This type of pigment has been shown to mask injury and mitigate ultraviolet stress (Ervin et al., 2004). The original commercial formulation, Two-Pack, consisted of the Civitas and Harmonizer packaged separately to be mixed on-site. A new pre-mixed single-product formulation, Civitas One™, was introduced in 2013.
The objectives of this project were to characterize the phytotoxic response of a mixed cool-season golf putting surface treated with Civitas, Harmonizer, or their combination in the field and determine how phytotoxicity is elicited in a growth chamber. Our hypothesis was that Civitas causes chronic phytotoxicity as a result of oil persistence and reduced gS.
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