Cutting Sour Rot in Wine Grapes with ROS

During 2023, Sawtooth Ag Research of Selma, CA tested JC 9465, a mineral oxychloride disinfectant, on wine grapes and cut sour rot in half while sharply increasing crop yield. Foliar application alone delivered a 50% drop in sour rot compared to the control and a 50% increase in crop yield.

The trial

The study was conducted on 6-year-old French Columbard wine grapes with a history of virus infections that emerged under seasonal stress. Four treatments were applied between April 26 and July 14, 2023.

Application schedule

• Soil irrigation: 78 mg/l concentration
• Foliar spray: 390 mg/l concentration, dosed at 0.05 oz/gal

The trial compared four groups: an untreated control, foliar spray only, soil irrigation only, and a combined foliar-plus-soil application.

Results

A 50% drop in sour rot compared to the control and a 50% increase in crop yield using JC 9465 through foliar application alone.

Yield improvements

• Foliar treatment produced 73 clusters per 2 vines, a 21.7% increase over the control's 60 clusters.
• Foliar spray produced 76 lbs per 2 vines, a 49.0% increase over the control's 51 lbs.
• The combined treatment achieved the maximum 50% sour rot reduction.

What is JC 9465?

JC 9465 is EPA FIFRA registered, USDA NOP certified, and USEPA Water approved.

How does sour rot differ from powdery mildew?

Sour rot is not a single pathogen and that is precisely why it is difficult. It is a complex — yeasts, acetic-acid bacteria, and the fruit flies that move both between berries — that establishes once the skin is compromised by any means: rain-driven splitting, bird or insect damage, or the natural cracking that follows a heat event on a tight cluster. A conventional fungicide programme aimed at a single fungal target does not address a mixed microbial community, and it does nothing about the vector.

The economic damage is disproportionate to the visible infection. Volatile acidity carries into the fermentation, so a modest percentage of affected berries can compromise a whole lot. Growers therefore end up either sorting aggressively at the crush pad or picking early, both of which cost yield or quality. A treatment that reduces incidence in the field is worth considerably more than the acreage number suggests.

Why does an oxidant beat a fungicide?

JC 9465 is a mineral oxychloride that delivers a family of reactive oxygen species — superoxide, hydroxyl radical, singlet oxygen, hydroperoxyl, and peroxide — at an oxidation potential of 2.8–2.9 V. Only fluorine is higher, at 3.06 V.

An oxidant does not have a single biochemical target, so it is not selective in the way a site-specific fungicide is: yeasts, bacteria, and fungal spores are all susceptible. That non-selectivity is a liability in some settings and an advantage here, because sour rot is a community rather than an organism. It also means there is no single-site resistance mechanism for the population to select for — a real consideration in a vineyard block that has been on the same fungicide chemistry for years.

Reading the trial numbers

Two things are worth drawing out. First, weight rose almost 49% while cluster count rose only 21.7%, which means the clusters themselves were heavier — more retained berries per cluster rather than simply more clusters set. That is the signature of reduced in-cluster loss, which is consistent with the sour-rot result rather than independent of it. Second, foliar application alone captured most of the yield benefit; the combined foliar-plus-soil programme was what achieved the maximum 50% sour-rot reduction. For a grower deciding where to spend, that distinction matters.

The vines were 6-year-old French Colombard with a history of virus infection that expressed under seasonal stress — not a clean, easy block. Treatments ran from 26 April to 14 July 2023: soil irrigation at 78 mg/L and foliar spray at 390 mg/L, dosed at 0.05 oz/gal.

How do you run the programme?

Application is dosed to an oxidation-reduction potential setpoint rather than a fixed concentration, so the programme corrects itself for organic load in the irrigation water. The in-field and post-harvest disinfection band is 650–750 mV; the ORP reference chart gives the full set of process targets. The effective pH range is 4–9, which covers most irrigation sources without adjustment, and installation is a metering pump, a storage tank, and an optional ORP controller — typically under 30 minutes.

JC 9465 is EPA FIFRA registered as a biocide and algaecide and certified under the USDA National Organic Program, which is what allows it in a certified organic block — see the EPA and USDA approval announcement. Related agricultural field work includes powdery mildew control, the Xylella fastidiosa trial, the citrus greening case study, and post-harvest food safety and quality. The full library sits under agricultural research and Food & Agriculture.

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