Executive Summary
The Limestone Grape and Wine Council investigated the use of Greenseeker® technology to determine if this technique would assist growers in being able to accurately quantify dieback caused by Eutypa in their vineyards when compared to the labour intensive ‘ground truthing’ technique.
The assessment was undertaken during the 2013/14 growing season on 6 Cabernet Sauvignon blocks located throughout the Limestone Coast. The Greenseeker® was run through each block in December with a follow up ground truth occurring within 2 weeks of the initial scan. Various amounts of each vineyard were ground truthed due to time constraints.
Results were variable with some vineyards producing higher degree of accuracy than others. This project identified a number of issues that would need further investigation before being confident that the technology is robust enough to be used by growers.
Introduction
Eutypa Dieback, caused by the fungus Eutypa lata, is a major trunk disease of grapevines (Sosnowski and Wicks 2012). Incidence of Eutypa in the Limestone Coast was recently assessed and the varieties Cabernet Sauvignon and Shiraz were observed with a mean incidence of 47% and 44% (Sosnowski et al. 2012). Disease incidence was greatest in vines 15+ years old increasing by 2% per year on average.
Vines infected with Eutypa often produce stunted shoots with chlorotic leaves; leaves may be cupped due to the toxins produced by the fungus and produce small, unevenly ripened fruit. Necrosis of wood results in wedge-shaped areas of stained tissue. The fungus grows slowly through the cordon and trunk eventually discolouring and killing the wood (Moller and Kasimatis, 1981, Sosnowski and Wicks 2013).
Ascospores infect grapevines through pruning wounds and germinate in xylem vessels. The mean rate of progression of wood staining due to Eutyparanged between 12 and 18 mm per yearin a study of eight cultivars, with a maximum of 50 mm per year recorded in individual Cabernet Sauvignon and Shiraz grapevines (Sosnowski et al., 2007).
Identification of the disease has traditionally been through ground surveys during spring at critical time points of grapevine phenology (E-L stages 12-23). However, this method is laborious and as such is time restrictive on the area available to survey on a given day.
The Greenseeker® is a mobile system with an active lighting optical sensor which emits high intensity light 660 +/-10nm in red and 770+/- 15nm in NIR wavebands (Mazetto et al. 2009), operated at cordon height levels. The light is reflected by the leaves and is captured by a photo diode in front of the sensor. Greenseeker® gives back the index values NDVI and red/NIR in real time and is a measure of the vine vigour status through a measure of ‘greenness’ which reflects the amount of chlorophyll in the leaves. Historically this technology has been used in broadacre agricultural pursuits particularly to look at requirements for nitrogen application and spraying weeds.
One operator in the Coonawarra wine region has used this technology over the past few years to initially assess vine vigour for potential improvements in wine quality by identifying batch lots for winemaking. It was identified during this process that the technology could be used for other uses including improving irrigation uniformity, vineyard biosecurity and identifying vine decline. For example, when Greenseeker® maps were analysed and compared on an annual basis, the change in vigour was identified and the information used to make a more informed decision on individual blocks long term viability (Figure 1).
For viticulture, there is potential to use the Greenseeker® as an early detection tool to measure vine decline associated with Eutypa. Currently very few operators within the viticultural industry have utilised this technology due mainly to a lack of confidence, knowledge and skills to adopt this type of technology along with the uncertainty in the accuracy of the data produced. It was the aim of this project to rapidly evaluate blocks for Eutypa decline and provide a quantitative assessment of Eutypa that is reproducible.
for full paper in PDF Eutypa Impacts: Groundtruth Infrared Technologies