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Petroleum-derived spray oils (PDSOs) have been used for pest management in horticulture and agronomy for over a century. Civitas™ is a new PDSO designed for use in the turfgrass industry. It is commonly mixed with low rates of pesticides to reduce the environmental impact and improve plant stress tolerance. Civitas can cause phytotoxicity, which has limited its acceptance by the turfgrass industry. Civitas is mixed with a green pigment called Harmonizer™ to sustain acceptable turfgrass color. A field study and a growth chamber study were designed to quantify phytotoxicity, understand the role of Harmonizer, and isolate the cause of Civitas-induced phytotoxicity. Civitas, Harmonizer, their combination (Two-Pack), and a water-only control were applied to a research putting surface in Ithaca, NY, during 2012 and 2013. Civitas and Harmonizer were applied every 2 weeks at the rates of 5.0 and 0.3 mL·m⁻², respectively. Visual turfgrass quality rating and canopy temperature were quantified several times weekly. Civitas caused chlorosis and decline in visual quality during both years. Harmonizer masked chlorosis but did not prevent a drop in stand density during the second field season. Treatments were replicated on annual bluegrass (Poa annua L.) in a growth chamber experiment. Civitas did not increase electrolyte leakage or alter the composition of cuticle; however, there were signs of oil persistence on the leaves and stomata and evidence of reduced gas exchange. Chlorosis resulting from oil persistence and reduced gas exchange is consistent with chronic PDSO phytotoxicity. This research demonstrated the potential for phytotoxicity with high rates of Civitas. Lower application rates likely reduce the potential for phytotoxicity but may also minimize the pest control benefits associated with the product.

A series of field studies were conducted from 1999 to 2005 in Ithaca, NY, at the Cornell Turfgrass Research Center as part of the National Turfgrass Evaluation Program (NTEP) to evaluate a collection of 78 fine-leaf fescue cultivars (Festuca spp.) for turfgrass quality, seedling vigor, and ability to inhibit the establishment of common annual and perennial weeds. Using these criteria, we evaluated the overall suitability of the cultivars for use in turfgrass settings, as well as their potential weed suppressive or allelopathic ability. The ability of fine-leaf fescue to displace weeds was visually evaluated by density-wise comparison, and several cultivars of the 78 studied consistently established well and provided good to very good suppression (greater than 70%) of common turf weeds when established at the same planting density. Other cultivars provided moderate (between 35% and 70%) to (< 30%) little weed suppression. Greater weed suppressivity is likely associated with the differential ability of fescue cultivars to establish rapidly and to form a dense canopy, as well as potential allelopathic interference. This study was conducted in conjunction with laboratory experiments that revealed that certain fine-leaf fescue cultivars produced phytotoxic root exudates that were released into the rhizosphere over time. Additional field studies conducted in Ithaca showed that cultivars Intrigue, Columbra, and Sandpiper were consistently more weed suppressive than the other fine-leaf fescues evaluated. Although our understanding of the dynamics of production and degradation of fine-leaf fescue root exudates in the rhizosphere is limited, recent field studies also suggest that allelopathic interference as well as the ability to rapidly establish influence subsequent weed infestation in fine-leaf fescue stands. From a more practical standpoint, certain fine-leaf fescue cultivars, including Intrigue, Columbra, Sandpiper, and Reliant II, could be recommended for use in low-maintenance turf settings in the northeastern United States due to their aesthetic appeal and their limited weed infestation in circumstances where herbicides are not applied.