Sensitivity of Hydrangea paniculata plants to residual herbicides in recycled irrigation varies with plant growth stage

Authors: POUDYAL, SHITAL - Michigan State University; Owen Jr, James - Jim; FERNANDEZ, R - Michigan State University; CREGG, B - Michigan State University

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2020
Publication Date: 5/15/2020
Citation: Poudyal, S., Owen Jr, J.S., Fernandez, R.D., Cregg, B. 2020. Sensitivity of Hydrangea paniculata plants to residual herbicides in recycled irrigation varies with plant growth stage. Water. 12(5):1402. https://doi.org/10.3390/w12051402.
DOI: https://doi.org/10.3390/w12051402

Interpretive Summary: Production of container-grown ornamental nursery plants is an intensive horticultural system that requires frequent inputs of water and agrochemicals to produce visually appealing plants. Irrigation in nurseries often generates substantial amounts of return flow, as 70-80% of applied water may be lost from nursery production areas. Irrigation return flow generated from nurseries often contains various agrochemicals, which, if released without remediation, may degrade neighboring ecosystems. Recycling nursery return flow for irrigation conserves water and can improve water security but it also holds some degree of risk to growers. Residual pesticides in recycled water may be phytotoxic to sensitive crops, and some growers have already reported evidence of phytotoxicity associated with pesticides. Chronic, low-dose exposure to pesticides in irrigation water can result in reduced plant growth, chlorosis, leaf distortion and other visible plant injuries. This study was focused on (1) quantifying the physiological and morphological effects of residual oryzalin and oxyfluorfen in simulated recycled water at various growth stages of the economically important crop Hydrangea paniculata Siebold. (Limelight), (2) identifying variation in sensitivity among growth stages of plants to residual herbicide exposure, and (3) determining the time required to recover from herbicide damage. Residual herbicides of oxyfluorfen or oryzalin present in recycled water may produce sub-lethal effects on woody ornamentals when used for irrigation. Young and growing leaves of hydrangea were more susceptible to herbicidal injuries compared to mature leaves. Early growth stages of hydrangea had a higher ratio of young to mature leaves and therefore are more prone to herbicide damage. Leaf injury from some herbicides will immediately begin to recover, while leaf injury from others will continue to increase before starting to recover. Damage caused oxyfluorfen that directly destroy photosynthesis apparatus is more severe and may permanently reduce growth if plants are exposed at early growth stages.

Technical Abstract: Recycling irrigation return flow is a viable option to achieve sustainability in horticultural production systems, but residual herbicides present in recycled water may be phytotoxic. The sensitivity of plants to residual herbicides may vary depending on the growth stage of the plant, in which case, if sensitive growth stages are avoided, the risk associated with using recycled water can be reduced. Here, we quantified the effect of residual oryzalin and oxyfluorfen exposure at various growth stages of Hydrangea paniculata. Exposure to both herbicides reduced plant growth, leaf visual rating, SPAD index, net photosynthesis, and light-adapted fluorescence of H. paniculata. Herbicide injury was greater for plants exposed to herbicides at early growth stages; however, the recovery rate of those plants was also rapid. For oxyfluorfen, plants produce healthy new growth immediately after the end of exposure, but for oryzalin, even newly formed leaves developed herbicide injury after the end of exposure, therefore leaf damage continued to progress before recovering. However, damage caused by residual herbicides exposure at all growth stages recovered over time. Physiological measurements such as SPAD index, net photosynthesis, and light-adapted fluorescence responded quickly to herbicides exposure hence provided an early indicator of herbicide damage and recovery.