High pH, Low Alkalinity Pond Water Used for Overhead Irrigation Does Not Affect Plant Growth of Select Flowering Shrubs1

In southeast U.S., pH of source water from ponds used for overhead-irrigating container crops can exceed the range (pH 5.8-7.0) for best management practices. Artificially maintaining this pH range is not common among producers using surface water for irrigation, nor is it known whether this would affect growth. Therefore, the objective was to test whether this source water affects growth of five flowering shrubs in nurseries in eastern North Carolina. Pond water at six nurseries with a pH range of 4.9-8.1 (control) was injected before irrigation with sulfuric acid (lower) or potassium bicarbonate (raise) onsite to maintain a pH of 5.8-6.2 (treatment). Ambient photosynthesis (Aambient) and stomatal conductance (gs) was measured in July, August, and September on leaves of forsythia (Forsythia x intermedia 'Mindor‘ ShowOff®) during irrigation runtime mini-experiments at three nurseries. For mini-experiments, pre- and post-treatment physiology was measured for plants receiving 0 (hand watered), 30, or 60 minutes of treated or nontreated overhead irrigation. Dry weight of all shrubs and gas exchange of forsythia was not affected by high pH, low alkalinity (<100 ppm) irrigation water. Southeastern producers using this source water for overhead irrigation may not need to adopt a system that reduces pH to improve growth. Index words:, Container-grown, plant physiology, photosynthesis, stomatal conductance, ornamental. Chemicals used in this study: Potassium bicarbonate, sulfuric acid. Species used in this study: fragrant abelia, Zabelia tyaihyonii (Nakai) Hisauti & H.Hara 'SMNAMDS‘ Sweet Emotion®; butterfly bush, Buddleia x ‘Miss Molly'; border forsythia, Forsythia x intermedia ‘Mindor‘ Show Off®; panicled hydrangea, Hydrangea paniculata Siebold ‘SMHPLQF' Little Quick Fire®; landscape rose, Rosa x ‘ChewPatout' Oso Easy®.

On-Farm Trials Reveal Significant but Uncertain Control of Botrytis cinerea by Aureobasidium pullulans and Potassium Bicarbonate in Organic Grapevines

Botrytis cinerea, a fungal pathogen that causes gray mold on grapes, can decrease yield, substantially reduce wine quality, and therefore cause significant economic losses. In a context of increasing awareness of environmental and human health, biopesticides are a potential alternative to synthetic chemical treatments to produce grapes and wine in compliance with high food standards. However, the effectiveness of biopesticides is not well known and more research is needed to help winegrowers assess their ability to control wine diseases. Our study aims to assess the efficacy of two commercial biopesticides, based on potassium bicarbonate and Aureobasidium pullulans, in reducing the incidence of gray mold (i.e., the proportion of grape bunches that are diseased). We use data from an on-farm trial network managed over 3 years (from 2014 to 2016) in a major wine producing region located in Southwestern France, and fit Bayesian generalized linear multilevel models able to take the variability of treatment effect across trials into account. The fitted models were then used to estimate the efficacy on incidence as a function of the severity (i.e., the proportion of diseased grape berries in a bunch) in an untreated plot in order to determine if the effectiveness of the treatments depends on the disease pressure. At average disease severity (i.e., 3%), the efficacy on disease incidence at the network level was equal to 20% [95% CI = (−0.1; 37.3)] and 13% [95% CI = (0.2; 24.7)] for potassium bicarbonate and A. pullulans, respectively. For both biopesticides, the efficacy on incidence for a new site-year is highly uncertain, but potassium bicarbonate had a lower uncertainty and a lower application cost compared to A. pullulans. Our results confirm that potassium bicarbonate is an interesting biopesticide under farming conditions in organic vineyards in southwestern France, but the amount of uncertainty points to the need for further research.