2018 ASHS Annual Conference

Nursery production is input intensive, demanding frequent irrigation and oftentimes multiple applications of pesticides throughout the season. Irrigation water lost to runoff or groundwater infiltration can move pesticides from production sites and contribute to non-point source pollution. Irrigation can be applied in ways which reduce runoff, such as incorporating micro-irrigation and sensor based technology. In this study, an experimental nursery was created with two 12 m (east to west) by 100 m (north to south) beds raised 60 cm above grade and divided into 8 sections each. The first 25 cm of the beds was backfilled with native soil and graded to the center and to the north or south side, covered with a pond liner, filled with 25 cm washed sand, graded as was the native soil, then covered with a landscape fabric as a production surface. Drainage ports were installed at the low points at the surface and at the subsurface pond liner and piped to collection tanks to collect water from runoff or infiltration. In 2017, three daily irrigation treatments, overhead at 19 mm, spray stake at 2 L per plant, or a set-point between 35% volumetric water content and container capacity, were use to determine water movement via runoff or infiltration. Three tank-mix pesticide applications were made at label rate and using industry standard practices. On 27 June acephate, bifenthrin, isoxaben and mefenoxam were applied; 8 August chlorpyrifos, triflumazole, oxyfluorfen and glyphosate were applied; 29 August prodiamine, glyphosate and thiophanate methyl were applied. The water collected in each tank over a 24 h period was measured to determine concentration and load for nitrogen and phosphorus approximately every 2 weeks and on 0, 1, 2, 4, 8 and 16 days after pesticide application. The movement of each compound in water as a result of irrigation method yielded differences in concentration and load exported from production. Spray stake irrigation reduced total runoff and infiltration water quantity relative to overhead irrigation. Pesticides were detected primarily in runoff water but also occurred in infiltration water. Dynamics of water, pesticide and nutrient movement will be discussed during the presentation.