BY: Kaan Kurtural, Luca Brillante, Johann Martinez-Luscher University of California Davis
Grape growing in California has a long history. With very few exceptions, vineyards have been managed uniformly. Although vineyard managers have known that variability in vineyards existed, there have been few tools at their disposal to quantify it or make attempts at correcting it.
In 2016, we used early season proximal sensing data generated by Terry Bates and colleagues to delineate management zones in three wine grape vineyards. This early season proximal sensing involved measuring soil electrical resistivity and canopy reflectance immediately after bud break. The results of these sensing efforts were then combined to derive management zones in these vineyards (Figure 1). Once management zones were delineated, a mechanistic work flow was followed to deduce what kind of treatments would be applied to each one of these zones (Figure 2).
The combined analysis of soil electrical resistivity, and early season canopy reflectance affected exposed leaf area per foot of row. Since exposed leaf area was shown to affect components of yield and berry composition canopy management treatments were applied to each management zone to remove the variability amongst zones. In exceptional cases where the variability was greater than 50% between zones and too large to coalesce, differential harvest of these zones were the only option. A threshold of 10 m2 of exposed leaf area was used to manipulate the canopies. The treatments applied varied between post-fruit set leaf removal, shoot removal or increasing applied water amounts to the grapevines. An example of the differential management set up in the Lodi region is shown in Figure 3.
In the initial year of the trial these differential management treatments were applied to strips of the vineyard rather than the whole management zone. These strips of vineyards consisted of at least five consecutive grapevines along the length of the row. For example, at the Lodi site, leaf removal was applied on the morning side seven consecutive grapevines, replicated four times at random with grower management as control (Figure 4).
Likewise, applied water treatments were also applied to small strips of vineyard as indicated by the management zone delineation. In this case, the aim was to increase the exposed leaf area. (Figure 5).
The applied treatments were successful in manipulating the exposed leaf area of the grapevines. After treatment application, the management zone deemed too vigorous by proximal sensing saw a reduction of exposed leaf area (Figure 6). Likewise, the management zone deemed not vigorous enough saw an increase in the exposed leaf area post-treatment application.
The manipulation in exposed leaf area resulted in a lack of differences in yield across management zones (Figure 7), which is one of the end of goals of the whole projects. This result was encouraging so that based on experimental results this year, the treatments may be applied to a whole block level to reduce variability at this site.