12 minute read
Cover Story
State of Matters: Copper Phthalocyanine Pigment
By Max Schlossberg, Ph.D. & Nathan Leiby M.S. (PSU AGRO ’21)
Unless noted, photo credits M.J. Schlossberg.
No more than zero artificial intelligence resources participated in the composition of the following article.
Cu II phthalocyanine (C₃₂H₁₆CuN₈), also known as viridian hue, pigment green 7, and phthalocyanine green G; is a brilliant green synthetic pigment utilized in numerous artistic and industrial applications. Like many popular dyes/pigments, phthalocyanine green G is both immiscible (water-fast) and recalcitrant (durable). It is a sizable pyrrole-benzene organometallic too (Fig. 1), with a molar mass just a fuzz over 576 grams. You’ve most recently seen it in auto paint or tattoo ink but were probably first introduced while mixing ‘Fore!’ fungicide back in the 20th Century.
To our PTC members operating in the southern hemisphere, Cu phthalocyanine is the pigment responsible for the verdant hue of the warm season turfgrass you just treated with dormancy colorant. For residents of the Commonwealth who utilize a spray pattern indicator with ‘Green’ in its name, Cu II phthalocyanine is likely the ingredient indicating where your last pass starts and ends. We included the ‘likely’ qualifier because some colorant products that appear green contain blue and yellow pigment combinations, rather than Cu phthalocyanine.
Considering regional interest, editorial constraints, and our research experience, we will limit discussion of Cu phthalocyanine to spray indicator and combination products applied to actively growing turfgrass systems in season. Readers seeking guidance on dormancy colorants or paint are encouraged to consult the useful and current ‘Guide to Using Turf Colorants’ by Dr. Grady Miller and Drew Pinnix of NC State Extension (https://content.ces.ncsu.edu/guide-to-using-turf-colorants).
Petroleum-derived Spray Oil (PDSO) plus Cu Phthalocyanine Combination Product
Owing to its low mammalian toxicity and environmental risk, Civitas Pre-M1xed Turf Defense™ (Intelligro, Mississauga, ON, Canada) comprises a popular and widely-available petroleum-derived spray oil (PDSO) plus Cu II phthalocyanine liquid product for inclusion in tank mixes as an indicator dye and/or product synergist. The impetus for the latter includes reports of reduced pesticide requirements when employing Civitas in IPM programs, and recognized benefits of Cu phthalocyanine and pesticide combinations. Civitas Pre-M1xed ain’t your mom’s ‘Oh Happy Plant Bath;’ as it features proven insecticidal properties, a fungicide resistance action committee (FRAC) classification of “not,” and an Organic Materials Review Institute certification permitting employ in organic production/management or where cosmetic pesticide use is prohibited.
Application of PDSO + Cu phthalocyanine products results in a coating of the plant canopy, to which leaf chlorosis has been attributed. This response has been correlated to reduced photosynthetic capacity arising from the inhibition of gas exchange. In the second year of continual treatment, repeated 17.3 fl. oz. per 1000 ft² (M) applications of PDSO or PDSO–colorant combination product to maintained putting greens reduced creeping bentgrass canopy quality, chlorophyll content, carbon dioxide exchange and transpiration rates. Semimonthly application of Civitas Pre-M1xed Turf Defense™ (8.5 fl. oz. per M) to an annual bluegrass putting green in Oregon from Sept. to June significantly reduced canopy density on plots subjected to double-rolling treatment five days a week.
However, studies describing ethephon-complementing, onetime, 17 fl. oz. per M application of Civitas to putting greens cohabited by creeping bentgrass and annual bluegrass proved synergistic in suppressing seedheads and did not incite a phytotoxic response. The current Civitas Turf Defense Pre-M1xed label (revised Nov. 2017) recommends an application rate between 8.5 and 17.3 fl. oz. per M, made on no less than 7-d intervals, either alone or in combination with routine tank mix ingredients.
Combination Product plus Urea-based Nitrogen
Although not uncommon practice of golf course superintendents, little research has evaluated urea-N and PDSO–colorant combination products when foliar-fertilizing cool-season turfgrass systems. In 2015, a colonial bentgrass fairway study was conducted by Gary Nolan & Dr. Wakar Uddin at the Valentine Turfgrass Research Center. End-of-season leaf clippings were collected and analyzed for N concentration, and those originating from plots repeatedly treated by Civitas Turf Defense Pre-M1xed (8.5 oz. per M) showed significantly greater tissue N than untreated plots. Once apprised of these results, we turfgrass nutrition researchers sought to uncover the how and the why. Foliar application of liquid N fertilizer is a popular approach to ensuring golf course turfgrass nutritional sufficiency in season. For turfgrass managers using primarily urea-N fertilizer, the N loss pathway of concern is ammonia (NH3) volatilization. As much as 11% of 0.4 lbs per M foliar urea-N applications to a golf course putting green were volatilized as NH3 within 24 h. More recent field evaluations showed between 3 and 8% of 0.15 to 0.2 lbs urea-N per M foliar applications were lost in the 24 h following golf course putting green treatment. Considering coating of the plant canopy by PDSO + Cu phthalocyanine is the mechanism by which reduced carbon dioxide exchange and transpiration rate is often attributed, the authors hypothesized Civitas inclusion may influence NH3 diffusion (volatilization) in the 0- to 48-hours following foliar fertilization of golf course fairways by urea-based N fertilizers.
Creeping Bentgrass Fairway Research, 2019 – 2020
Complementing semimonthly soluble N applications with 8.5 fl. oz. Civitas Pre-M1xed per M of creeping bentgrass fairways (in 1.5 gal./M carrier volume) didn’t affect 0- to 48-hour NH3 volatilization loss (Fig. 2) but significantly improved the mean fairway canopy dark green color index. Which in turn, raised some questions like ‘How?’ and ‘Why?’ and ‘What is the fate of these combination products?’ The open-access (free) paper describing all specific aspects of our fairway research is available at http://www.mdpi.com/2076-3298/10/10/176
The companies that developed and introduced Civitas, PetroCanada and Intelligro, have proven committed and steadfast in their support of university research. Yet there remains little insight into how the spray oil and Cu phthalocyanine components interact with the living turfgrass canopy over time from application and what their ultimate fates are. These same questions arose in the co-author’s thesis research on putting greens (Fig. 3): Is all Civitas applied absorbed, or bound to vegetation? How does carrier volume affect Civitas distribution throughout the canopy?
And perhaps the most poignant of questions: Could phthalocyanine green absorption by plant tissue cause the darker green color and greater vigor observed of the treated plots? While support for this potential mechanism exists, readers may not consider its origin objectively neutral. But we’re not implicating ‘X’ or ‘Meta’ or whatever the leading, zero-cost source of ‘opinions that fascinate’ currently is. Rather, a national company’s online technical data sheet that claims their unique pigment additive ‘stimulates the plant’s natural metabolism and can improve turf color, density, vigor, consistency and strength, from the inside out. Unlike dyes and paints, this unique pigment additive is absorbed into the plant for longer lasting affects (sic).’
Regarding our 2019 – 20 research, analysis of the fairway clipping yield (shoot growth) data identified significant spray treatment effects. Specifically, in the second half of the 2019 and 2020 growing seasons, the top statistical grouping for mean clipping yield consisted of all Civitas-containing treatments. This was curious, but like the above technical data sheet claims, not readily refutable — since the literature lacked reports on the mass Cu phthalocyanine and/or spray oil expected to remain on turfgrass canopies by time from spray treatment.
As a proxy, mass retention of an 8.5 oz. per M Civitas Pre-M1xed Turf Defense application to dry clippings within a polystyrene tray was measured <1 and 1440 minutes following spray application. Approximately 1.2% of the initially applied spray remained as dry solids on the leaf tissue one day (1440 minutes) following. Considering the 0.86 g/mL specific gravity of Civitas Pre-M1xed, and confirming the water component of the spray evaporated (per negative controls), the data indicate 0.006 lbs of solid Civitas residue would be expected to remain on 1000 ft2 of canopy one day following the described spray treatment. This mass was significantly less than the observed difference between clipping yields collected from Civitasvs. un-treated plots in the second half of either growing season.
So How Did PDSO Plus Cu Phthalocyanine Increase Canopy Color and Shoot Growth?
A national company (different from the one quoted above) markets its premium pigment additive with claims ‘it provides natural green turf color for up to one month and reflects potentially harmful near infrared (NIR) light, which may improve turfgrass quality and vigor.’ Getting back to our 2019–20 research, we definitely observed improved turfgrass color and vigor of Civitas-treated plots. But the frequently collected fairway canopy reflectance data showed Civitas treatment reflected significantly less NIR (760- or 810-nm) than equally Nfertilized or untreated bentgrass over several 10-d post-application periods.
So how else could Cu phthalocyanine foster increased canopy color and shoot growth? The product label of a different (third) national company claims it is an advanced colorant formulation that resists the harsh effects associated with long periods of high temperature and intense UV light exposure. Now this follows results of research published in 2004 describing treatment, UV-B (290320 nm) exposure, and assessment of Kentucky bluegrass sod health. However, a suite of greenhouse and field research conducted on various turfgrass systems in Virginia from 2014–15 evaluated low rates of Civitas Pre-M1xed and two other commercial Cu phthalocyanine spray pattern indicators. Canopy spectroradiometer readings collected 1 day after treatment showed significantly less reflection of UV-A radiation (320–400 nm) than from untreated plots.
So perhaps, but how else? Well you’ve surely noticed the only phthalocyanine green containing product we’ve mentioned by name is Civitas Pre-M1xed. This seemed prudent given Civitas is the only phthalocyanine green containing product our lab has evaluated at The Pennsylvania State University since 2018. Again, Civitas Pre-M1xed didn’t affect NH3 volatilization in the two days following application at an 8.5 fl. oz. per M rate ….but did foster increased mean canopy color and shoot growth in the second half of each study year. This may be an occasion when evaluation of additional data helps us link cause to effect, i.e., N content of clipping yields and fertilizer N recovery (FNR).
Leave it to the Turfgrass Nutritionists to Implicate a Nutrient
Nitrogen analysis of homogenous Civitas Pre-M1xed reveals a mean N concentration of 1.0%. Considering healthy bentgrass leaf clippings collected from our Declaration fairway ranged from 3.27 to 5.99% N by mass, any of the 0.006 lbs Civitas residue we determined to remain in 1000 ft2 of canopy, one day following application, would be more likely to dilute leaf N content than increase it. Yet, on average, clippings collected from Civitas and N fertilizer-treated plots contained 0.22% greater absolute leaf N than plots treated by N-fertilizer alone. Thus, while systematic complementation of foliar N fertilizer by Civitas Pre-M1xed did not directly influence volatilization loss, cumulative reapplications somehow enhanced N availability.
The origin of the 1.0% N in Civitas is primarily the Cu II phthalocyanine pigment (C32H16CuN8). Having a reference 19.5% N content, this organic N is neither immediately assimilable by plants nor disclosed on the label. However, the estimated N load from Cu II phthalocyanine delivered in each 8.5 fl. oz. application of Civitas Pre-M1xed equals 0.005 lbs N per M. In the last five of the six yield collections, Civitas complementation enhanced fertilizer N recovery (FNR) by a margin exceeding the Civitas N load delivered in the most recent application. However, only in the last two yield collections did Civitas complementation enhance FNR by a margin exceeding the sum of the most recent Civitas N load and the calculated least significant difference (LSD 5%). Meanwhile, cumulative Civitas N load by the end of the 2020 season totaled nearly 0.1 lbs N per M, only 3.3% of the total fertilizer N applied over both growing seasons.
So where does that leave us…in simple terms? Our data indicate Civitas applied to turfgrass isn’t entirely removed with clippings. Rather, irrigation/rain, traversing equipment, foot traffic, canopy maturation, and mowing ultimately translocate a significant fraction of Civitas applications to the underlying soil/ rootzone. The Cu phthalocyanine component (pigment) of Civitas, or any containing colorant product, is a big organic molecule with a C:N ratio of 3.4!! For those of you who have taken TURF 435, you know that’s a rich organic amendment. Yet this Civitas N accounts for less than half the 8.7% greater mean FNR demonstrated by Civitas-complemented treatments to the creeping bentgrass fairway.
What’s the Greenest Slow-release N Fertilizer You Never Knew?
Meanwhile you’re probably wondering how is this durable, recalcitrant, pyrrole-benzene decomposed and mineralized in soil? Well, if we depended only on agronomic and soil science journals, a supporting answer would prove challenging. Yet, industrial and environmental engineers have conducted extensive research on bioremediation of industrial waste from the textiles industry. In aerobic environments, wood-rot fungi have proven extraordinarily proficient at degrading synthetic dyes. For the fungi Irpex lacteus and Pleurotus ostreatus, soil Cu phthalocyanine might as well be a juicy meatball or tofu curd (pick the analogy that best suits your dietary preference). Given adequate moisture, Cu phthalocyanine carbon is promptly assimilated and its organic N mineralized, both at a rate directly related to temperature and soil oxygen content. This is likely why the magnitude of Civitas-induced N nutrition was greatest in late summer; it was when soil temperatures were high and accumulated soil Cu phthalocyanine greatest.
We are currently conducting lab incubations of soil-incorporated Cu phthalocyanine to determine rate and degree of microbial degradation and N mineralization. Thus, there is more to follow, but the plant response observed in our field research does not make application of spray oil and Cu phthalocyanine combination product any less enigmatic of a cultural practice. We’re identifying a component of influence for now, and that is Cu phthalocyanine may be the greenest slow-release N fertilizer you’ve never heard of. So, the next time you wonder what it is about repeated applications of Cu phthalocyanine-containing product(s) that make(s) your turfgrass appear vigorous and healthy (Fig. 4), remember Cu phthalocyanine’s ~20% N content. It may just have something to do with it!
