Sometimes a little stress is a good thing?

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.

Over the two years of the field study, Kreuser and Rossi used a mixed Poa annua/creeping bentgrass (L-93) putting green located in Ithaca, N.Y. Treatments were simple: 1) Civitas (PDSO) alone at 16 ounces/1,000 square feet (5 milliliters/square meter) — a high rate for this oil for putting surfaces; 2) the green pigment alone 0.94 fluid ounce/1,000 square feet (0.3 milliliter/square meter); 3) Civitas + pigment; and 4) no Civitas or pigment (the untreated control). Spray volume was 2 gallons/1,000 square feet (810 liters/hectare), and all treatments were applied every two weeks in August and September in year 1 and from May through August in year 2. Collected data included turfgrass quality and canopy temperature. Similar treatments were also used in growth chamber studies on a stand of pure annual bluegrass, and these experiments were used to measure detailed things, including gas exchange, cuticle composition and membrane integrity. For the growth chamber studies, treatments were applied and data were collected 48 hours after application.

Field trials clearly showed an interaction between Civitas and the pigment, but it differed in each year of the study. In 2012, when the pigment and Civitas were applied together, turfgrass quality in the Civitas + pigment plots was equal to that found in the control and pigment-only plots. In 2013, a similar effect was observed from May through July 24, but after that date, quality in the plots that received both Civitas at the high rate and the pigment dropped below acceptable limits, and a decline in tiller density led to severe thinning. In the growth chamber studies, application of Civitas affected stomatal conductance. While the leaf membrane or cuticle composition of the turfgrass plants were not affected by treatment, the oil persisted on the leaves and reduced gas exchange appearing to clog the stomates.

So, why in the world would people consider applying this material? Well, in this study, Civitas was applied at a high label rate (5% w/v) for a single application to a putting green in season. That rate is far above the more typical rates (~ 2% w/v) that have been studied for horticultural oils. Additional work conducted to pinpoint correct rates suggests a variable rate and application frequency range depending on targeted stress (disease, moisture, traffic, etc.) and turf type (warm- vs. cool-season). A variety of other field studies from California to Florida to Ontario, Canada, indicates that Civitas has potential, but requires some thought and tweaking by the superintendents and additional research. The concepts of induced systemic resistance introduce a different way of thinking about turfgrass management, and they may challenge some of our conventional turfgrass management practices.

Source: Kreuser, William C., and Frank S. Rossi. 2014. The horticultural spray oil, Civitas, causes chronic phytotoxicity on cool-season golf turf. HortScience 49:1217-1224.

Reference: Cortes-Barco, A.M., P.H. Goodwin and T. Hsiang. 2010. Induced systemic resistance against three foliar diseases of Agrostis stolonifera by (2R, 3R)-butanediol or an isoparrafin mixture. Annals of Applied Biology 157:179–189. 

Beth Guertal, Ph.D., is a professor in the department of crop, soil and environmental sciences at Auburn University in Auburn, Ala., and the editor-in-chief for the American Society of Agronomy. She is a 19-year member of GCSAA.