Editor's note: In her Verdure column for the June 2015 GCM, Dr. Beth Guertal discusses research on the use of petroleum-derived spray oil on turf.
Over the past few years a petroleum-derived spray oil (PDSO) has been the subject of much chitchat in the turfgrass market. When new technology arrives to marketplace, exploring the mechanism of action and limits to use are key roles for land-grant scientists. It is a role of land-grant researchers to explore the utility of new technologies. Spray oils have been used in horticulture since the 1800s. Sold under the trade name Civitas, the PDSO has been shown to improve plant stress tolerance by activating the plant defense system. “Induced systemic resistance (ISR),” occurs when something (in this case, application of Civitas) primes genes that are involved in plant protection and stress tolerance. A range of things can trigger ISR, including various strains of Bacillus and Pseudomonas, and rhizobacteria. Civitas, when used as a part of a disease management program, has been shown to reduce pesticide, nutrient and water use.
Civitas causes phytotoxic effects when applied to foliage. To help mask this injury, a green pigment was added to the product. But the problem is that the source of the phytoxicity might be twofold. First, there is the injury to the leaf itself (the phytoxicity, which the green pigment can mask), and then additional injury could be caused by inhibition of stomatal conduction, essentially clogging the plant’s pores, which are used for air and water movement. That’s what then-Ph.D. student, Bill Kreuser, and Professor Frank Rossi set out to evaluate. The goal of the research project was to elucidate the mechanism of action at a field level and a physiological level, since other researchers (Cortes-Barco et al. 2010) had already shown the molecular basis of defense activation caused by Civitas. Kreuser and Rossi wanted to examine how much phytotoxicity was caused by Civitas applied alone, and whether the phytotoxicity was due to persistence of the oil on the leaf, or if injury occurred because stomates appeared clogged.