Essential oils for disease management in organically grown fruit crops

Project Director: Ali Sarkhosh, University of Florida

Project overview

Plant diseases cost the temperate and tropical fruit industry billions of dollars in crop losses each year. Organic growers use a wide array of tools to reduce losses, including resistant varieties, biological controls, and the use of approved fungicides. With the future of copper and sulfur-based pesticides in question, organic fruit growers need innovative options for the control of fungal diseases. Certified organic plant essential oils (EOs) may have the potential as a pest management tool in the production and post-harvest period of various fruit crops as they act on a broad spectrum of plant diseases and are safe for the environment and human consumption.

In 2020, a trans-disciplinary team of agricultural researchers based at the University of Florida began on-farm and laboratory evaluations of certified organic plant essential oils on common fungal diseases of peach, blueberry, mango, and avocado in five states (Florida, Georgia, South Carolina, California, and Hawaii). The overarching goal of this project is to increase organic orchard productivity, allow for the production of low-residue fruit crops, and offer growers an organic spray program using organic plant EOs.

Farmer takeaways

The essential oil formulations tested did not effectively control fungal diseases in field evaluations of blueberry, peach, avocado, or mango
- Non-EO-derived OSO (Polyoxin D) showed some promise as an organically approved fungicide in peach.
- Non-EO-derived Kocide®-2000-O was effective for controlling select fungal pathogens of avocado and mango.
Variety had more of an effect on disease incidence than EO treatment in blueberries, highlighting the importance of using disease resistant varieties as part of an IPM program
Thyme oil as a post-harvest treatment (e.g., fumigation or dipping) can reduce the severity of brown rot in stored peaches

Project objectives and approach

Testing of selected plant EOs for plant safety and plant disease control in lab and greenhouse trials

In 2023, on-farm peach trials investigated control of brown rot with fungicide sprays in Florida. Fungicide treatments consisted of combinations of OSO, PureSprayGreen (an OMRI listed mineral oil), Thyme Guard and Cinnerate. An additional on-farm trial was established on avocado and mango. Fungicide treatments consisted of an untreated control, TG, TA, Kocide®-2000-O (KO – an OMRI listed copper fungicide) or TG+KO. In-field assessments of phytotoxicity of the different fungicides were recorded, along with disease incidence and severity.

On-farm testing of disease suppression with various mixtures and concentrations of EOs

In 2023, on-farm blueberry trials were set-up to evaluate essential oils alongside other organic fungicides for control of fruit rot diseases (Anthracnose ripe rot, Botrytis fruit rot, and Alternaria fruit rot) and leaf spot diseases (Anthracnose leaf spot, blueberry leaf rust, and Septoria leaf spot) at three organic blueberry production sites in GA and FL.

Fungicide treatments consisted of the OMRI-listed products OSO (Polyoxin D), Thyme Guard (TG), Timorex Act (TA), and Cinnerate (CI) at recommended low and high rates, and a 5x concentration of the high rate. In-field assessments of phytotoxicity of the different fungicides were recorded, along with disease incidence and severity.

Testing the ability of EOs to extend fruit shelf life

Postharvest fruit decay incidence, fruit quality, and sensory evaluation for all fruit crops as affected by treatments in the field (in situ) and in the lab (in vivo) were determined.

Key findings

In-vitro, essential oils have potential to suppress the growth of certain fungal pathogens, but can also have no effect, or even a growth-enhancing effect

ThymeGuard (TG), followed by oregano and savory EOs showed efficacy against all fungal isolates from blueberry regardless of species or origin.
The same inhibitory pattern was observed with Monilinia isolates growth where they were highly or completely inhibited by TG, TO, OO and SO.
Timorex Act (TA) showed very low efficacy against all tested isolates and at times enhanced growth at some or all concentrations across species.
In vitro, biofungicides with thyme oil (TO, TG) or cinnamon oil (CI) completely inhibited the mycelial growth of E. perseae at active ingredient concentrations higher than or equal to 125 µl/l and showed fungicide activity at a minimum active ingredient concentration of 250 µl/l and 125 µl/l, respectively.

The in vitro effects of EO’s on disease development were much different than the on-farm result

In the field, EO’s were not effective in controlling fungal pathogens in blueberry or peach. Variety had more of an effect on disease incidence than EO treatment in blueberry. In peach, OSO (Polyoxin D) showed promise as a fungicide.

Commercial essential oil formulations can be used safely when label rates are followed. Use caution after bloom

In the first year of field trials, essential oils did not damage leaves when applied at the recommended rates, but in the second year, phytotoxicity was observed in blueberry plants after multiple Timorex Act applications and in peach after multiple ThymeGuard applications.

The EO’s tested were not as effective as a standard copper fungicide for disease control in avocado and mango

The two treatments that included KO were the most effective treatment for control of powdery mildew, blossom blight, anthracnose, algal leaf spot, and scab, while few differences were observed between the TA, TG, and untreated control.

EO’s have limited efficacy in reducing post-harvest fruit rot

Pre-harvest spray of blueberry, peaches, mango, and avocado with EO’s did not reduce disease incidence
Thyme oil vapor fumigation and dipping fruit in ThymeGuard solution post-harvest can reduce the severity of brown rot in peaches.

Resources

Essential oils for managing anthracnose in mango (Mangifera indica): laboratory results do not translate into field efficacy

In Vitro Antifungal Activity of White Thyme, Oregano, and Savory Oils Against Five Monilinia fructicola Isolates from the Southeastern United States

Genome Sequence Resource of the Avocado Scab Pathogen Elsinoe perseae

Biocontrol Potential of Essential Oils in Organic Horticulture Systems: From Farm to Fork

Prevention and Management of Peach Diseases in Florida

Evaluating Fungal Disease Management in Organic Blueberry Production

Plant Derived Essential Oil Products: Safety and Efficacy for Organic Peach and Blueberry Disease Control [Video 40:50 to 60:01]

Hawaii Mango Research Projects Workshop Presentation and Q&A Recording

USDA - Project Report - OREI 2020-51300-32181

Location

Florida

Collaborators

Jonathan Crane, University of Florida

Guido Schnabel, Clemson University

Jeffrey Brecht, University of Florida

Danielle Treadwell, University of Florida

Bruce Schaffer, University of Florida

Jonathon Oliver, University of Georgia

Daniel Carrillo, University of Florida

Juan Carlos Melgar, Clemson University

Patricia Manosalva, University of California, Riverside

Romina Gazis, University of Florida

Jeffrey Williamson, University of Florida

Phil Harmon, University of Florida

Andrea Kawabata, University of Hawaii

Lisa Keith, USDA-ARS

Region

Southern

Topic

Disease Management

Year Published

2023