Proper Use of Aerial Diagnostic Maps to Improve Vineyard Performance

By Kevin Gould

You’ve probably heard of NDVI (Normalized Difference Vegetation Index) or EVI (Enhanced Vegetation Index) maps, which are helpful in understanding the relative health of grapevines. Typically generated from multispectral imagery gathered by satellites, airplanes or drones, these maps are based on the principle that healthy plants reflect less red visible light than unhealthy plants because healthy plants absorb more of it as they are engaged in higher rates of photosynthesis. In other words, aerial sensors detect less reflected red light from vigorous vines because more photosynthesis is taking place, meaning those vines are healthier. Formatted to a color scale representing differing levels of photosynthetic activity, these “vigor” maps depict areas where vines may be unhealthy and require attention (or in some cases, too healthy and thus not likely to produce grapes of desired quality). Vineyard managers and viticulturists can then investigate these areas of off-vigor to determine the cause and treatment in an effort to achieve greater block uniformity.

The most common question I’m asked about these maps is: “The maps look good, but what do they mean?” To answer that, let’s take a look at a typical map, shown below.

The scale for the color coding is in the lower left corner (for ease of reference, I’ve inserted some numeric values directly onto this map). You can see on the southern block, the lower tip shows the highest vigor (.60), and then the vigor drops as you move north (.55, then .50, then .45).  Moving east across the top, the vigor generally increases slightly, then decreases.  While it’s up to vineyard management to decide the appropriate target level of vigor, these maps can be invaluable in achieving block uniformity.  In this example, if the target vigor is .50, then steps could be taken to reduce vigor in the southern block and raise vigor in the .45 sections of the upper blocks.

Low or high vigor can be caused by a variety of factors, including moisture, nutrition, pests, disease, soil, hail, pruning, etc. One of the most interesting analyses we found was the map shown here. 

Notice the blue band of high vigor near the northern edge. The owner believes that in the past a creek ran from the upper right corner of this block, down to where the tree line juts out next to the “.65” marker (the creek currently runs along the top edge of the block, then turns south and follows the tree line shown).  That former creek may have created strong soil conditions, which is consistent with the gradual drop in vigor as you move away from its prior path. The owner is now considering options for dealing with it.

Additional formats of these vigor maps allow users to see plant health on specific rows and, in some cases, specific vines.  Below is a version of the first map above which allows the user to see vigor on a vine-by-vine level. These maps can be zoomed in for greater detail – I’ve superimposed a zoomed in view to demonstrate.

Other types of maps can also be helpful in diagnosing specific conditions in a vineyard.  Leafroll Disease Detection maps are created by aerial sensing of the specific spectral signature of the disease towards the end of the season.  Supported by published scientific research, these maps can pinpoint areas where the disease is present.  As shown in this example, the user can zoom in to identify infected vines.

Finally, there are geo-referenced mobile apps available that allow the vineyard managers and viticulturists to walk directly out to areas of disease or off-target vigor and visually identify the affected vines.  This feature is extremely helpful in determining the best course of action.

These aerial maps are just some of the analytical tools available to viticulturists and vineyard operators as they strive to produce the best grapes possible.  Combined with leading edge crop management techniques, the results can be dramatic.