Etiology and Management of Rind Breakdown of Mandarins

Etiology and Management of Rind Breakdown of Mandarins J. H. Connell, University of California Cooperative Extension, Butte County, Oroville, California H. Forster (1), G. Driever, D. Thompson, and J. E. Adaskaveg (2) (1) University of California, Davis (2) University of California, Riverside

The Problem In fall 2002, an epidemic rind disorder occurred on Satsuma mandarin throughout the central valley of California from Kern to Butte Co. The initial problem developed three to four days after an early November rain and development continued following additional rain storms.

Mandarin Rind Breakdown Paradise, 2002

Literature Review üFawcett (1936) described rind breakdown in California on Navel and Valencia oranges and attributed the disorder to wet weather and temperature changes.

Objectives 1. Determine the etiology of rind breakdown of mandarins ü Collect diseased fruit and isolate from symptoms ü Reproduce the disease using wetting and temperature treatments (& pathogens? ) ü Monitor the field environment that occurs prior to development of disease

Objectives 2. Evaluate the effect of fungicides and water repellants on the incidence and severity of rind breakdown of mandarins ü Initiated trials in selected mandarin orchards. ü Compared fungicides, water repellants, and combinations on the incidence of rind breakdown of Satsuma mandarins.

Fruit Isolations and Inoculations

Biotic cause of mandarin rind breakdown? Fungal isolations fall/winter Grove 1 (Fresno Co. ) 66% of lesions Alternaria sp. 34% of lesions Fusarium sp. Grove 2 (Tulare Co. ) 70% of lesions Ulocladium sp. * Isolations show no 20% of lesions Fusarium sp. consistent pathogen Grove 3 (Butte Co. ) from orchards with the 18% of lesions Alternaria sp. disorder. 41% of lesions Fusarium sp. 29% of lesions Macrophomina sp. 6% of lesions Cladosporium sp. Grove 4 (Fresno Co. ) 83% of lesions Alternaria sp. Grove 5 (Fresno Co. ) 80% of lesions Alternaria sp. Fungi isolated are common air-borne or soil-borne fungi. These fungi are commonly found on plant surfaces.

Laboratory Fruit Inoculations with Fungal Isolates from Mandarin Rind Breakdown Inoculations Fusarium sp. AN. 419 Healthy Areas Water-Soaked Fusarium sp. AN. 420 Alternaria sp. AN 421 Alternaria sp. AN 422 Alternaria sp. AN 423 0 20 40 60 80 100 Incidence of decay (%) Incidence of Decay in Inoculation Areas Summary: Non-inoculated fruit did not develop symptoms, whereas fruit that were soaked in water had a higher incidence of decay than fruit inoculated in healthy areas. Fruit were soaked in water for 6 hr and rind symptoms developed in approximately 5 hr. Inoculations were done using aqueous spore preparations of each fungal isolate (10 5) either on healthy fruit surfaces or in symptomatic areas after the water soaking treatment. Inoculated fruit were kept at 100% humidity for three days.

Fruit Treatments - - Initial Lab Evaluations

Effect of Postharvest Fruit Coatings in Reducing Symptoms of MRB in Water-Soaked Fruit - Laboratory Study Treatments Control Decco 202 Decco 400 0 20 40 60 80 Incidence (%) 100 Control Summary: Fruit coatings decreased the incidence of the rind disorder. Furthermore, nonwater soluble (e. g. , Decco 400) coatings developed less symptoms than water soluble coatings (e. g. , Decco 202) Fruit were treated using labeled preparations of fruit coatings and dried at 30 C for 30 min. Treated fruit did not develop symptoms after 24 hrs. Fruit were then soaked in water for 6 hr, placed in a humidity chamber for 18 hrs, and evaluated.

Effect of Oil and Anti-Transpirants in Reducing Symptoms of MRB in Water-Soaked Fruit - Laboratory Study Soaked control Vaporgard Oil Dry Control 0 20 40 60 80 Incidence (%) 100 0 0. 5 1 1. 5 2 Severity 2. 5 Summary: Non-water soluble fruit treatments decreased the incidence of the rind disorder. These products are registered on citrus as antitranspirants or insecticides and 3 could be used as water repellants. Fruit were treated at labeled preparations of the treatments and air-dried for 24 hrs. Fruit were soaked in water for 10 hr, placed in a humidity chamber for 48 hrs, and then evaluated. Severity was a scale of 0 -3 (0 = no symptoms and 3 symptoms greater than 25% of the fruit surface area.

Conclusions – Objective 1 Cause of mandarin rind breakdown and reproduction of the disease ü Trials indicated rind breakdown symptoms primarily resulted from environmental factors causing oil gland injury. ü Epiphytic fungi including Alternaria spp. were not found to be virulent pathogens of healthy tissue. ü The disorder was reproduced in the lab by soaking orange-colored fruit in water for several hours. ü The disorder can be reduced with water repellents.

Objectives 2. Evaluate the effect of fungicides and water repellants on the incidence and severity of rind breakdown of mandarins üInitiated field trials in selected mandarin orchards. üCompared fungicides, water repellants, and combinations on the incidence of rind breakdown of Satsuma mandarins.

Field Trials in Butte County To evaluate fungicides and water repellants (oils and antitranspirants)

Efficacy of Fungicides in Reducing Mandarin Rind Breakdown Butte Co. 2002 Check Topsin 75 WP Abound 2 F Pristine 38 WG 0 20 0 5 40 60 80 100 2003 Check Abound 2 F Topsin 75 WP Vapor. Gard Omni Oil Topsin 75 WP+Oil 10 15 20 25 MRB Incidence (%) Air-blast sprayer calibrated to 100 gal/A. Four quadrants of each replication tree (5 replication/treatment) were evaluated for the incidence of MRB. Symptoms were observed on the exposed portion of outside fruit in all quadrants of the trees.

Effect of fungicides and water repellants on the incidence and severity of rind breakdown of mandarins in field trials Field trial, Butte Co. 2004 Trt Rate (/A) Check Oct. Nov. 22 9 19 26 --- --- Abound 12. 8 oz @ --- Vapor Gard 1 gal @ @ --- @ Vapor Gard 1 gal @ --- --- Omni Oil 6 qt-0. 75% @ @ --- @ Omni Oil 6 qt-0. 75% @ --- --- Vapor. Gard /Nordox 1 gal/6 lb @ --- --- Protected --- --- --- Incidence of MRB (%)* a a b b b ** 0 5 10 15 20 25 30 35

2005 Season Efficacy of preharvest treatments in reducing MRB in California

2005 Precipitation in Butte County…. . Northern vs. Central California 35 Parlier, CA Precipitation (mm) 30 Durham, CA Totals: 27. 5 mm 144. 2 mm 25 20 15 10 5 Date Data from CIMIS. 15 /2 00 5 12 / 20 05 8/ 12 / 20 05 1/ 12 / 24 /2 00 5 11 / 17 /2 00 5 11 / 10 /2 00 5 11 / 20 05 3/ 11 / 27 /2 00 5 10 / 20 /2 00 5 0

Summary --- üForanti-transpirant three years in Butte Co. , an or an agricultural oil significantly reduced rind breakdown whereas fungicides were mostly ineffective. üFurthermore, trees physically protected in each of two seasons had no symptoms developing on fruit.

Conclusions – Objective 2 Management of mandarin rind breakdown üOur trials indicate MRB symptoms on Satsuma mandarins can be reduced using an anti-transpirant or an oil. üFungicides were ineffective in Butte Co. trials done over four seasons. üThe disorder begins to occur at the color break stage of fruit development.

Benefits to the Industry 1. Correct identification of the cause of mandarin rind breakdown allows the development of strategies to protect fruit and reduce crop losses in the future. 2. Understanding the disorder also provides an opportunity for good fungicide stewardship and cost savings to growers.

Joe Connell, Farm Advisor, Butte County 538 -7201