2018 ASHS Annual Conference

Irrigation is an important tool to increase grapevine vigor and fruit yield across the Midwest USA. However, with enhanced pressure on water resources, vineyards are soon likely to experience water restrictions. Growers will need relevant information about grapevine water levels in order to efficiently irrigate their vineyards. This research focused on defining water stress thresholds for ‘Edelweiss’ (Minnesota 78 x Ontario) grapevines using midday leaf water potential (Ψ_md) and high resolution thermal infrared images from two different thermal sensors. Potted grapevines were subjected to a range of water stress treatments to evaluate water content levels (Control – fully irrigated and 2 to 14 days of water being withheld). After the 14-day water withholding period, thermal images were taken of the vines using an expensive Flir S62 camera and an inexpensive Flir C2 camera. Immediately following, a mature fully-expanded leaf was excised from the plant and tested for Ψ_md. Fully irrigated and 14-day dry vines exhibited a Ψ_md of -8.7 bars and -13.3 bars, respectively. The grapevines exhibited a mild, moderate and severe water stress level at 8, 10 and 12 days-dry, respectively (Ψ_md of -12 bars, -12.5 bars and -13 bars). The Crop Water Stress Index (CWSI) more accurately predicted Ψ_md when using leaf temperature data collected by the inexpensive Flir C2 thermal camera (p = 0.016). The CWSI has been shown to be a good indicator of vine water status in more arid growing regions, but has not been well documented in more humid climates. The CWSI calculated from the Flir C2 temperature data had moderate correlations to Ψ_md (r² = 0.511). Our results document the thresholds for mild, moderate and severe water stress levels for greenhouse grown potted ‘Edelweiss’ grapevines. Additional research and refinement is necessary in order to use the CWSI to accurately predict Ψ_md in humid growing regions.