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Youbin Zheng*, Linping Wang, Weizhong Liu, John Sutton, and Mike Dixon

Copper is one of the essential micro-nutrient elements for plants, but when in excess, is toxic to plants and other living organisms. Electrolytically generated copper and cupric sulphate are increasingly used by the greenhouse industry to control diseases and algae in hydroponic systems. However, there is little information regarding appropriate strategies for employing copper in greenhouse crop production. We investigated the physiological responses, growth and production of several ornamental crops (miniature rose, chrysanthemum and geranium) and greenhouse vegetable crops (pepper, cucumber, and tomato) with respect to Cu2+ concentration in the root zone. Tests were conducted using plants grown in nutrient solution, Promix and rockwool. Results showed that phytotoxic levels of Cu2+ were dependent on the crop species and growing substrate. Plants grown in nutrient solution exhibited symptoms of phytotoxicity at lower Cu2+ concentrations than those on the solid substrates. The ability of copper to control Pythium aphanidermatum and green algae was evaluated under both laboratory and greenhouse conditions. Copper was effective in suppressing green algae in nutrient solution, but did not control Pythium effectively. This presentation is a comprehensive summary of the research conducted over the last three years by our group on copper application in greenhouse systems.

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Youping Sun, Guihong Bi, Genhua Niu, and Christina Perez

paclobutrazol at 60 mg·L −1 were effective for height control and lateral branching ( Hilgers et al., 2005 ). Symptoms of phytotoxicity are a known issue with most plant growth retardants. The severity of phytotoxicity depends on plant species or cultivar and

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Yuanshuo Qu, Ryan M. Daddio, Patrick E. McCullough, Stacy A. Bonos, and William A. Meyer

annual bluegrass postemergence when applied at 0.5 to 1 kg·ha –1 two to five times per year ( Flessner et al., 2013 ; Koo et al., 2014 ; Xiong et al., 2015 ). Despite various research, little has been published to date on the phytotoxicity of

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Tori Lee Jackson, Mark G. Hutton, and David T. Handley

). Oils applied to corn can damage the plant tissues if applied in a high enough dose ( Hazzard, 1998 ). The efficacy of oil treatments has been demonstrated in some experiments, but phytotoxicity or damage to the developing ear from reduced pollination

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Raymond A. Cloyd and Nina L. Cycholl

A greenhouse study was conducted from Oct. 1999 through Feb. 2000, and Mar. 2001 through Apr. 2001, to determine the potential phytotoxic effects of selected insecticides on Spanish lavender (Lavandula stoechas L.), oregano (Origanum vulgare L. `Santa Cruz'), rosemary (Rosmarinus officinalis L.), St. Johnswort (Hypericum perforatum L. `Topaz'), wolly thyme (Thymus vulgaris L. `Wolly'), and nutmeg thyme (Thymus vulgaris L. `Nutmeg'). Insecticides used for the study were Beauveria bassiana Strain GHA, pyrethrin [+ piperonyl butoxide (PBO)], azadirachtin, potassium salts of fatty acids, two rates of cinnamaldehyde, paraffinic oil, and capsaicin. Visual observations of phytotoxicity were made 7 days after the final application. Pyrethrin, potassium salts of fatty acids, and both rates of cinnamaldehyde were consistently more phytotoxic than the other insecticides. Despite the phytotoxic effects from some of the insecticides, new growth that emerged following treatments compensated for the initial damage, and the herbs were still saleable.

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Ruiqin Bai and Deying Li

after treatment (WAT). The development of phytotoxicity was slower with the diesel compared with gasoline. Diesel killed the existing perennial ryegrass within 2 weeks leaving the dead leaf tissue with a greasy black appearance. The hydraulic fluid

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Daniel F. Warnock

Late season control of whitefly is problematic in many production ranges as systemic insecticides may not provide full season control. Most commercially available contact insecticides are not labeled for use on fully colored poinsettia, Euphorbia pulcherrima, plants due to potential phytotoxicity or residue on colored bracts. Recent formulation changes in TriStar make late season applications possible. This study assessed phytotoxicity and residue impacts of two formulations of TriStar on potted poinsettias. On 4 Aug. 2004, rooted cuttings of 47 poinsettia cultivars obtained from four commercial suppliers were transplanted into pots containing a soilless medium. A total of 235 cuttings were used to arrive at five pots per cultivar. Plants were grown using standard production techniques. On 11 Nov. 2004, all plants were fully colored and treated with TriStar 70 WSP or TriStar 30SG at maximum label rates. Phytotoxicity and residue levels were assessed 7 days later using a 1 to 9 visual scale. Overall the formulations had few negative impacts on poinsettias. Phytotociticy ratings were minimal for most cultivars; however, some cultivars, such as `Silverstar Red' expressed an elevated level of phytotoxicity. Dark colored cultivars showed more residue than light colored cultivars. The TirStar 30SG formulation had the least amount of residue. TriStar 30SG may be an acceptable insecticide for late season control of whitefly on poinsettia crops. Producers are cautioned to test cultivars for phytotoxicity before applying to an entire crop as some cultivars are sensitive to TriStar 30SG.

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Jorge H. Siller-Cepeda, Leslie H. Fuchigami, and Tony H.H. Chen

The effects of hydrogen cyanamide (H2CN2) on budbreak and phytotoxicity of l-year-old potted peach trees [Prunus persica (L.) Batsch. cv. Redhaven] over a wide range of concentrations at several stages of dormancy were studied. Endodormancy (180° GS; degree growth stage) began on 1 Oct. Maximum intensity of endodormancy (270° GS) was reached after the plants were exposed to 320 chill units on 1 Nov., and 50% of the buds were broken at 860 chill units on 1 Dec. Five concentrations of H2C N2 (0, 0.125, 0.25, 0.5, and 1.0 m) were applied on 1 and 15 Oct., 1 and 15 Nov., and 1 and 15 Dec. 1990. All concentrations promoted budbreak; however, percent budbreak and phytotoxicity depended on concentration and timing of application. The most effective concentration (greatest budbreak and lowest phytotoxicity) was 0.125 m H2CN2 on all treatment dates. Phytotoxicity was evident at all application dates but was greatest at the highest concentrations. Plants were most resistant to H2CN2 at maximum intensity of endodormancy. Hydrogen cyanamide-induced budbreak was highest during the later stages of endodormancy (295 to 315° GS). Treatments applied during the ecodormancy stage (340° GS) inhibited and delayed budbreak and damaged buds and stems. Chemical name used: hydrogen cyanamide (H2CN2, Dormex).

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L. Gene Albrigo and Jude W. Grosser

In Florida, pesticides, nutritional and growth regulators are often sprayed in tank mixes to reduce sprayer use. Many individual spray components are phytotoxic and result in spray burns in combination or if applied with adjuvants. The toxicity level of standard spray materials is not known and new product testing for phytotoxicity is not routine. Three tests were developed to allow testing of cellular and whole fruit susceptibility to spray chemicals. Cell suspension cultures initiated from `nucellar derived' embryonic callus of `Hamlin' sweet orange were grown in log phase for 2 weeks with various levels of test chemicals. Fresh weight increase was measured. Peel disks of orange or grapefruit were grown for 4 weeks on solid media. Color changes and callus growth were used to evaluate phytotoxicity. Dilute sprays and droplet applications to on-tree-fruit were used to evaluate individual and combinations of chemicals with and without spray adjuvants. The 3 tests combined effectively demonstrated levels of phytotoxicity and are useful for testing new citrus production chemicals.

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Stephen S. Miller and Thomas Tworkoski

the United States in 1989 ( Dennis, 2000 ). Most of the other chemicals have been less satisfactory as a result of inconsistent flower thinning or foliar phytotoxicity. However, fruit thinning of apples and peaches by chemical thinners may be