Investigating Alternative Pathogen Management through Sensor-driven Irrigation

Substrate pathogen management is important in greenhouse and container nursery operations, particularly if irrigation water is being recycled for re-use.  Often times, fungicides are used as a preventative cultural practice even if recycled water is treated.  Routine fungicide applications are expensive, can encourage chemical resistance and can be environmentally unsound.  We hypothesize that we can reduce the need for preventative fungicides, by irrigating based on daily plant water use, and creating an antagonistic environment for pathogen movement.  We conducted a replicated study in a commercial container-nursery in Maryland using precision irrigation management, based on soil-moisture volumetric water content (VWC) data.  Three irrigation strategies, namely time-based (TB), set-point based (SP) and set-point + interrupted (SPI) were applied to two Rhododendron species (R. catawbiense and R. chinoides).  Half (24) of the plants in each of ten replicate blocks per irrigation treatment were inoculated with Phytophthora cinnamomi from samples bulked in the lab.  Substrate VWC content from ten 10-HS sensors (Decagon Devices, Inc. Pullman WA) in each treatment were continuously monitored and logged by a combination of EM50R (monitoring) and nR5 (control) nodes (Decagon Devices), that transmitted data to a computer located in the nursery office.  The data were downloaded and visualized using Sensorweb (Carnegie Mellon) software.  Remote access to the data and control node settings is accessed over the internet through a browser.  Irrigation in the SP and SPI treatments was monitored and controlled through the sensor system which applied irrigation according to the VWC set-point.  The TB irrigation irrigated 4-6 times per day (adjusted seasonally) for 40 seconds per irrigation.  Water-use volumes were recorded for each irrigation treatment throughout the study using flow meters.  Plants each species were destructively harvested at the beginning of the experiment in July, 2013; thirty-six randomly selected plants (18 inoculated, 18 non-inoculated) were destructively harvested in November; Canopy volume and shoot extension were measured three times during summer and fall, 2013.  Roots and substrate samples were taken to assess infection rates at the same times.  Irrigation water applications were significantly lower for SP and SPI treatments compared to TB irrigation.  Average shoot mass and leaf area, although not significant between treatments after six months, were higher for both SP and SPI treatments, compared to TB irrigation.  Shoot dry mass and leaf area also averaged higher for non-inoculated vs. inoculated plants, indicating that these differences might become significant by the next harvest in June, 2014.