Abstract
Managers of ornamental nurseries are increasingly reusing runoff water as an irrigation source, but residual pesticides in recycled water may result in plant phytotoxicity on crop plants. Our study focused on understanding the responses of container-grown landscape plants to residual pesticides in irrigation water. Hydrangea paniculata ‘Limelight’, Cornus obliqua ‘Powell garden’, and Hosta ‘Gold standard’ were exposed to various concentrations of isoxaben, chlorpyrifos, and oxyfluorfen (0, 0.15, 0.35, 0.7, and 1.4 mg/L of isoxaben; 0, 0.05, 0.1, 0.2, and 0.4 mg/L of chlorpyrifos; and 0, 0.005, 0.01, 0.015, and 0.02 mg/L of oxyfluorfen) applied as overhead irrigation. After three months of application, we assessed the dry weight biomass, growth, and parameters related to photosynthetic physiology (SPAD chlorophyll index, light-adapted chlorophyll fluorescence, and photosynthesis carbon dioxide response (A/Ci) curves. We also sampled plant leaf, stem, and root tissues for residual pesticides. The effects of the pesticides were pesticide-specific and taxa-specific. Exposure to oxyfluorfen resulted in visible injury in all three taxa and reduced total biomass, chlorophyll index, and photosynthesis in Hydrangea and Hosta. All three taxa absorbed and retained pesticides in leaf and stem tissues. Growers should follow best management practices to reduce exposure from irrigation with runoff, particularly for herbicides with post-emergent activity.
Highlights
Horticulture is a major industry in the U.S In 2014, the sale of floriculture, nursery, and specialty crops were worth $13.8 billion, up by 18% since 2009 [1]
Isoxaben caused a slight reduction in PSII efficiency, but neither isoxaben or chlorpyrifos affected dry weight biomass, photosynthetic biochemistry, or caused visible leaf injury as oxyfluorfen did
This response likely reflects the fact that oxyfluorfen is an herbicide that has post-emergent activity and has the potential to affect sensitive plants following prolonged low-dose exposure
Summary
Horticulture is a major industry in the U.S In 2014, the sale of floriculture, nursery, and specialty crops were worth $13.8 billion, up by 18% since 2009 [1]. Irrigation is often applied based on general rules of thumb, such as 19 mm of water per day. These application rates often greatly exceed plant water needs and result in substantial runoff [2,3]. Runoff generated from container nurseries may contain various pesticides, and if released without treatment, surface water contamination and toxicity to aquatic life can occur [5,6,7]. To cope with new regulations and ensure water security, the capture and reuse of runoff water is increasing among nursery growers [8,9,10]. While capturing and reusing runoff may be a practical solution to reduce contaminants in neighboring ecosystems, growers’ concerns about potential negative impacts of residual pesticide on crop growth and quality
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