Phytophthora Species Associated with Plants in Constructed Wetlands and Vegetated Channels at a Commercial Plant Nursery Over Time

Constructed wetlands have been used for decades in agricultural settings to remediate nutrients and other agrichemicals from irrigation runoff and drainage; however, little is known about the presence and distribution of Phytophthora species within irrigation runoff water being treated in constructed wetlands. Therefore, we collected plant samples from within vegetated runoff collection channels and treatment stages of two constructed wetland systems receiving irrigation runoff at a commercial plant nursery in Cairo, GA, to determine if roots of wetland plants were infested by species of Phytophthora. Samples were collected 12 times, at 1- to 2-month intervals, over a 19-month period, from Mar. 2011 through Sept. 2012. The sample period covered all four seasons of the year, so we could determine if the association of Phytophthora species with roots of specific plant species varied with season. Approximately 340 samples from 14 wetland plant species were collected, and 22 isolates of Phytophthora species were recovered. Phytophthora species were typically isolated from plants in channels receiving runoff water directly from plant production areas; Phytophthora species were not detected on plants where water leaves the nursery. No seasonal patterns were observed in plant infestation or presence of species of Phytophthora. In fact, Phytophthora species were rarely found to be associated with the roots of the wetland plants collected; species of Phytophthora were found infesting roots of only 6.5% of the 336 plants sampled. Species of Phytophthora were not found to be associated with the roots of golden canna (Canna flaccida), lamp rush (Juncus effusus var. solutus), duckweed (Lemna valdiviana), or sedges (Carex sp.) during the study period. The exotic invasive plant species marsh dayflower [Murdannia keisak (33% of samples infested)] and alligatorweed [Alternanthera philoxeroides (15% of samples infested)] were found to have the first and third highest, respectively, incidences of infestation, with smooth beggartick (Bidens laevis) having the second highest incidence of samples infested (22%). Management of invasive species in drainage canals and constructed wetland systems may be critical because of their potential propensity toward infestation by Phytophthora species. Plant species recommended for further investigation for use in constructed wetlands to remediate irrigation runoff include golden canna, marsh pennywort (Hydrocotyle umbellata), pickerelweed (Pontederia cordata), and broadleaf cattail (Typha latifolia). The results from this study provide an important first look at the associations between species of Phytophthora and wetland plants in constructed wetland systems treating irrigation runoff and will serve to further optimize the design of constructed wetlands and other vegetation-based treatment technologies for the removal of plant pathogens from irrigation runoff.

Runoff pH Influences Nutrient Removal Efficacy of Floating Treatment Wetland Systems

Floating treatment wetlands (FTWs), a modified constructed wetland technology, can be deployed in ponds for the treatment of nursery and greenhouse irrigation runoff. The pH of nursery and greenhouse operation irrigation water varies from 3.3 to 10.4 across the United States. Water flow rate, plant species selection, and variable nutrient inputs influence the remediation efficacy of FTWs and may interact with the pH of inflow water to change nutrient remediation dynamics. Therefore, an experiment was designed to quantify the effect of pH on the growth and nutrient uptake capacity of three macrophyte species using a mesocosm FTW system. ‘Rising Sun’ japanese iris (Iris ensata), bushy bluestem (Andropogon glomeratus), and maidencane (Panicum hemitomon) were grown for two 6-week periods and exposed to five pH treatment levels representing the range of nursery and greenhouse irrigation runoff, 4.5, 5.5, 6.5, 7.2, and 8.5, for a total of 15 plant and pH combinations. Water was treated with either hydrochloric acid to decrease the pH or sodium hydroxide to increase the pH. The pH-adjusted solutions were mixed with 12 mg·L−1 nitrogen (N) and 6 mg·L−1 phosphorus (P) fertilizer (64.8 g·m−3 N and 32.4 g·m−3 P). Differences in pH impacted both N and P removal from the FTW systems for two of the three species studied, maidencane and bushy bluestem. Higher pH treatments reduced nutrient removal efficacy, but plants were still capable of consistently removing nutrients across all pH treatments. Conversely, ‘Rising Sun’ japanese iris maintained similar remediation efficacies and removal rates across all pH treatments for both N and P, possibly due to the ability to acidify its rhizosphere and modify the pH of the system. Average N and P loads were reduced by 47.3 g·m−3 N (70%) and 16.6 g·m−3 P (56%). ‘Rising Sun’ japanese iris is a promising plant for use in highly variable conditions when the pH of irrigation runoff is outside the typical range (5.5–7.5). Results from model simulations poorly predict the nutrient availability of P and ammonium in effluent, most likely due to the inability to determine plant and biological contributions to the system, such as N-fixing bacteria.

Environmental impact of intensive farming in sloping areas

The increased demand for food causes intensive farming with high yield production and large water consumption to extend significantly. Depending on soil properties, seasonal rainfall, surface drainage and water resources, hence the consumption-infiltration balance, the ground water table might be raised or depleted; soils could be saturated or remain partly saturated with negative pore pressures. As a result sloping grounds may become prone to shallow slides, as mudflows, or deep seated movements, involving large volumes of soil, especially after rupture of major watering lines or after long uncontrolled irrigations. Within this framework the paper investigates the possible effects of replacing grassland with intensive apple farming on the stability conditions of slopes. Apples require frequent watering, especially during spring and summer to meet qualitative and quantitative productive standards. Also, sprinkler irrigation is often used to protect against hail. From the precipitation, irrigation, runoff, evaporation and plant transpiration balance, the evolution of the pore water pressure distribution within an average year is calculated. Then the modified shear strength of the unsaturated-saturated soils is determined and the factor of safety against sliding is calculated.

Comparison of Five Detection and Quantification Methods for Phytophthora ramorum in Stream and Irrigation Water

Propagules of Phytophthora ramorum, the causal agent of sudden oak death (SOD) and ramorum blight, can be recovered from infested stream and nursery irrigation runoff using baiting and filtration methods. Five detection methods, including pear and rhododendron leaf baits, Bottle O’ Bait, filtration, and quantitative polymerase chain reaction (qPCR) performed on zoospores trapped on a filter were compared simultaneously in laboratory assays using lab or creek water spiked with known quantities of P. ramorum zoospores. The detection threshold for each method was determined and methods that could be used to quantify zoospore inoculum were identified. Filtration and qPCR were the most sensitive at detecting low levels of zoospores, followed by wounded rhododendron leaves, rhododendron leaf disks, and pear baits. Filtration, qPCR, and leaf disks were able to quantify P. ramorum zoospores ranging from 2 to 451 direct-plate CFU/liter while wounded leaves and pear baits appeared to be better at detection rather than quantification. The ability to detect and quantify P. ramorum inoculum in water will assist scientists, regulatory agencies, and nursery personnel in assessing the risk of spreading P. ramorum in nurseries and landscape sites where untreated infested water is used for irrigation.