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

View the project final report

Commodities

• Fruits: grapes

Practices

• Education and Training: participatory research
• Pest Management: chemical control, cultural control

Pinot noir is currently the highest value wine grape variety in the Eastern US and is among the top cultivated varieties in Ohio (NY Department of Agriculture & Markets 2018, USDA 2017). The variety, however, is known for tight clusters and susceptibility to late-season bunch rot diseases. Recent work has found pre-bloom early leaf removal (ELR) to reduce cluster compactness in tight clustered varieties, while reducing incidence and severity of bunch rot (Acimovic et al. 2017, Hed and Centinari 2018). However, the effects of ELR are variable and highly dependent on variety and localized environmental conditions (Hickey and Wolf 2018). Currently, ELR is considered an experimental practice with little commercial adoption in Ohio.

This proposal sought to introduce ELR to wine grape producers in Ohio, as well as to further understand the physiological impacts of ELR. One major focus of the research effort will be on validating mechanical leaf removal as a cost-effective means to achieve the benefits of ELR treatments. Additionally, this project addressed the diversity of trait expression within the Pinot Noir variety by determining the impacts of ELR on widely planted varietal clones. Importantly, this proposal prioritizes the creation of extension resources to guide ELR adoption in Ohio.

The project set up research projects at three locations, including the Ashtabula Agricultural Research Station and two commercial locations. At the Ashtabula Agricultural Research Station, a trial examined the effect of ELR on the Mariafeld, Pommard, Dijon #115, and Foundation Plant Materials Service #29 clones of Pinot Noir. ELR Treatments were applied in 2019 and 2020 at trace bloom and a selection of data was collected throughout the ripening season of each year. These measurements surveyed rot levels, fruit set metrics, berry counts, yield, canopy density, and juice chemistry , among other parameters. In 2019 and 2020, the Mariafeld clone was particularly sensitive to ELR treatment application, evidenced by fruit set and berry count data. The effect of ELR and the other clones in question was less consistent between years and across various metrics. 

A clonal study was also conducted in 2019 and 2020 at a commercial vineyard site in the Grand River Valley region of Ohio. Here, the research team examined the clones Mariafeld, Dijon 777, and 115 clones of Pinot Noir. Similarly to the work conducted at AARS, ELR was applied manually at trace bloom and the effects were studied throughout the ripening period. Both the Mariafeld and Clone 777 responded to the treatment with improvements fruit quality metrics such as brix and total phenolics.   The application of ELR treatments resulted in a statistically significant reduction in bunch rot across all three clones. However, all three treatments experienced a commercially significant amount of rot, despite ELR treatment, affirming that ELR is not a standalone solution to bunch rot or a replacement for targeted sprays.

At a second commercial vineyard site in the Grand River Valley, a trial was conducted in 2019 to compare the efficacy of mechanical and manual leaf removal. Manual ELR was applied at trace bloom, as was defoliation with a Collard E2200 leaf removal machine. Data was collected to determine whether there were any effects in yield, vine performance, or fruit chemistry when applying ELR mechanically, rather than manually. Across the suite of metrics, numbering more than 10, no statistically significant (p<0.05) differences were observed between the efficacy of mechanical and manual ELR. This finding suggested the mechanical ELR was an acceptable substitute for manual ELR and that financial and practical, rather than horticultural, considerations should drive that investment decision.

Generally, our project concluded that ELR is a helpful practice for vinifera wine grapes in Ohio and similar climates. It did not provide control of bunch rot in our trials, but when used in conjunction with an effective spray program, it is thought to be additive towards that goal. The application of ELR did have positive effects on fruit chemistry in some clones, though the effect was inconsistent. Mechanical ELR was drastically faster than manual ELR and did not produce any measurable negative effects, in comparison to manual ELR. More work is needed still on whether or how to integrate ELR in scenarios where vines have experienced recent spring or winter cold injury.

1. Provide best practice guidance to Ohio vineyards on the implementation of pre-bloom early leaf removal (ELR) as a management strategy for late season bunch rot diseases.
   1. Our project evaluated this strategy and found it to be inadequate as a standalone measure in preventing sour rot and, to an extent, botrytis bunch rot.
2. Determine the suitability of mechanization for pre-bloom ELR application in Pinot Noir.
   1. Mechanical ELR was found to be a suitable alternative to manual ELR.
3. Identify sensitivity differences to ELR application among popular Pinot Noir clones.
   1. Of the clones evaluated, the Mariafeld clone of Pinot Noir was found to be sensitive to ELR treatment application.
   2. Other clones (Pommard, 115, 777, 29) exhibited a mixed response to ELR treatment application.
4. Produce cost-benefit analysis of manual and mechanical ELR application methods.
   1. Mechanical ELR was found to be approximately 60x faster than manual ELR.
   2. Our estimates hold that conversion from manual ELR to mechanical ELR will have a positive ROI after approximately the 250th acre serviced.