Non-destructive monitoring of foliar fungicide efficacy with hyperspectral sensing

Authors: GAMBHIR, NIKITA - Cornell University; PAUL, ANGELA - Cornell University; QIU, TIAN - Cornell University; COMBS, DAVID - Cornell University; HOSSEINZADEH, SAEED - Cornell University; Underhill, Anna; JIANG, YU - Cornell University; Cadle-Davidson, Lance; GOLD, KAITLIN - Cornell University

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2023
Publication Date: 2/20/2024
Citation: Gambhir, N., Paul, A., Qiu, T., Combs, D.B., Hosseinzadeh, S., Underhill, A.N., Jiang, Y., Cadle Davidson, L.E., Gold, K.M. 2024. Non-destructive monitoring of foliar fungicide efficacy with hyperspectral sensing. Journal of Phytopathology. https://doi.org/10.1094/PHYTO-02-23-0061-R.
DOI: https://doi.org/10.1094/PHYTO-02-23-0061-R

Interpretive Summary: The frequent fungicide applications required to manage grapevine powdery mildew are costly and lead to widespread fungicide resistance. A method of monitoring fungicide residue could help growers spray less and delay fungicide resistance. This study evaluated whether hyperspectral sensing (visible and infrared spectra) can quantify fungicide efficacy on grape leaves. Fungicides and biocontrols were applied onto ‘Chardonnay’ grapevines in vineyards or greenhouses. Hyperspectral readings were recorded at multiple days post application. Fungicide efficacy was estimated after powdery mildew inoculation in a laboratory. Hyperspectral readings differentiated fungicides and biocontrols from the untreated control. These readings were moderately correlated with disease severity. Prediction accuracy depended on the fungicide and the time-point measured. Results suggest that hyperspectral sensing can be used to monitor fungicide efficacy, which could reduce fungicide applications and promote sustainable grapevine protection.

Technical Abstract: Frequent fungicide applications are required to manage grapevine powdery mildew (Erysiphe necator). However, this practice is costly and has led to widespread fungicide resistance. A method of monitoring in-field fungicide efficacy could help growers maximize spray-interval length, thereby reducing costs and the rate of fungicide resistance emergence. The goal of this study was to evaluate if hyperspectral sensing in the visible to shortwave infrared range (VSWIR, 400–2,400 nm) can quantify foliar fungicide efficacy on grape leaves. Commercial formulations of metrafenone, Bacillus mycoides isolate J (BmJ), and sulfur were applied on Chardonnay grapevines in vineyard or greenhouse settings. Foliar reflectance was measured with handheld hyperspectral spectroradiometers at multiple days post application. Fungicide efficacy was estimated as a proxy for fungicide residue and disease control measured with the Blackbird microscopy imaging robot. Treatments could be differentiated from the untreated control with an accuracy of 73.06% for metrafenone, 67.76% for BmJ, and 94.10% for sulfur. Change in spectral reflectance was moderately correlated with cube root of area under the disease progress curve for metrafenone and sulfur treated samples (R2 = 0.38; 0.36, respectively) and with sulfur residue (R2 = 0.42). BmJ treatment impacted foliar physiology by enhancing leaf mass/area and reducing nitrogen and total phenolic content as estimated from spectral reflectance. Results suggest that hyperspectral sensing can be used to monitor in-situ fungicide efficacy and prediction accuracy depends on the fungicide and the time-point measured. The ability to monitor in-situ fungicide efficacy could facilitate more strategic fungicide applications and promote sustainable grapevine protection.