Early Leaf Removal Strategies for Bunch Rot Reduction in Pinot Noir Clones

A side by side comparison of mechanical versus manual ELR was conducted at a local vineyard in Harpersfield Twp., Ohio. Perhaps most importantly,  mechanical ELR was drastically quicker to apply than the manual application of ELR. AARS crew averaged roughly 2 minutes per vine to apply ELR manually. Our calculations show Mechanical ELR application to require roughly 2 seconds, per vine, making it approximately 60 times faster than manual application. Our data did not demonstrate a statistically significant difference in the sunlight penetration or remaining leaf area produced by the various treatments, which suggests that the treatment applications produced a similar level of the intended defoliation. The treatments did not produce significantly different Titratable Acidity or Total Phenolics in 2019. In 2019, we found a weak tendency towards higher brix in the manual defoilation treatment (p<0.10). Generally, the conclusion of this project on the question of mechanical vs. manual ELR was that mechanical ELR is an adequate replacement, and is substantially more time efficient. With the two methods being relatively equal in effect, our conclusion was that the decision whether to purchase the equipment involved should focus more on financial considerations, such as the ability to meet the capital outlay, the size and productivity of the vineyard as it relates to potential return on investment, as well as other factors.

The other two trials in this project related to the efficacy of ELR, applied manually, in various clones of Pinot Noir. One trial was conducted at the Ashtabula Agricultural Research Station (AARS), involving the following clones: Mariafeld, Pommard, Clone 29, and Clone 115. The impetus for this trial was the observation, over numerous years, as to the unique characteristics of the Mariafeld clone found in that vineyard. Typically, we observe that the Mariafeld Clone has significantly looser clusters, with fewer berries per cluster, than other Pinot Noir clones. Data collected in this trial indicated that not only were both of those points true in general, but also that Mariafeld tended to have a higher level of response to ELR treatment.

With regards to berry counts, both Mariafeld and Clone 115 had significantly fewer berries (p<0.05) in the ELR treatment groups, compared to the controls. The other two clones did not exhibit a significant difference in berry count between the ELR and non-ELR groups. Mariafeld and Clone 115 also had significantly lower yield in their ELR groups (p<0.05), which likely related to the discrepancies in berry count between treatment and control. Only the Mariafeld and Pommard clones had a significant difference in the level of rot found in its control and treatment groups. At this site, the rot level was relatively low across all clones. The treatment group of the Mariafeld clone was found to have higher brix, lower Titratable Acidity, and higher total phenolics than the Mariafeld non-ELR control group. The treatment group of the Pommard clone had higher brix than its control, but did not differ on other juice quality metrics. Juice quality differences in the other clones did not pass a test for statistical significance.

At a local commercial vineyard site, a similar trial was conducted with the Mariafeld, Dijon 777, and Dijon 115 clone of Pinot Noir. Berry counts per cluster for all three clones were significantly lower in the ELR treatment groups, compared to the non-treatment group (p<0.05). The juice chemistry was positively affected by the ELR treatment group, across all three clones, meaning that brix were higher, TAs were lower, and Total Phenolics were higher in the treatment group. Average yields tended to be numerically lower for the treatment groups, though only that for Clone 115 passed the threshold for statistical significance (p<0.05). The level of rot observed in the treatment groups was significantly lower than the non-ELR control groups. However, even the ELR treatment groups sustained a high level of rot at this site, rendering any statistical differences there mostly irrelevant in terms of outcome to the grower.

Generally, this project reached several clear conclusions about the role of ELR in Pinot Noir, most of which echo those existing elsewhere in scientific literature. We found that at both sites, application of ELR tended to produce positive effects in juice quality metrics such as brix, Titratable Acidity, and Total Phenolics. Our results indicate that it can have a positive contribution towards controlling rot, but as demonstrated at the aforementioned commercial site, ELR does not necessarily function as a substitute for other measures in controlling rot. Elsewhere, literature differentiates between the improved ability of ELR in reducing botrytis and fungal bunch rots, in contrast to the yeast, bacterial, insect-driven case of Sour Rot. With regards to clonal differences, our results provide compelling evidence that the Mariafeld clone is particularly sensitive to ELR, in addition to having naturally looser clusters in general. Other clones exhibited more inconsistent patterns of relative response to ELR. Interestingly, the Mariafeld clone did perform somewhat differently at the two sites. Our team is in contact with several nurseries to identify whether a particularly loose strain of Mariafeld may be found in the AARS planting.