Etiology and Management of Rind Breakdown of Mandarins

1. 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) • University of California, Davis • University of California, Riverside

2. The Problem In fall 2002, an epidemic rind disorder occurred on Satsuma mandarin throughout thecentral valley of California from Kern to Butte Co. The initial problem developed three to four days after an early November rain anddevelopmentcontinued followingadditional rain storms.

3. Mandarin Rind Breakdown Paradise, 2002

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

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

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

7. Fruit Isolations and Inoculations

8. 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.

9. Laboratory Fruit Inoculations with Fungal Isolates from Mandarin Rind Breakdown Inoculations 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. Fusarium sp. AN. 419 Healthy Areas Fusarium sp. AN. 420 Water-Soaked 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 Fruit were soaked in water for 6 hr and rind symptoms developed in approximately 5 hr. 5 Inoculations were done using aqueous spore preparations of each fungal isolate (10 ) either on healthy fruit surfaces or in symptomatic areas after the water soaking treatment. Inoculated fruit were kept at 100% humidity for three days.

10. Fruit Treatments - - - Initial Lab Evaluations

11. Effect of Postharvest Fruit Coatings in Reducing Symptoms of MRB in Water-Soaked Fruit - Laboratory Study - Treatments Summary: Fruit coatings decreased the incidence of the rind disorder. Furthermore, non-water soluble (e.g., Decco 400) coatings developed less symptoms than water soluble coatings (e.g., Decco 202) Control Decco 202 Decco 400 0 20 40 60 80 100 Control Incidence (%) 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.

12. Effect of Oil and Anti-Transpirants in Reducing Symptoms of MRB in Water-Soaked Fruit - Laboratory Study - Summary: Non-water soluble fruit treatments decreased the incidence of the rind disorder. These products are registered on citrus as anti-transpirants or insecticides and could be used as water repellants. Soaked control Vaporgard Oil Dry Control 0 0.5 1 1.5 2 2.5 3 0 20 40 60 80 100 Severity Incidence (%) 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.

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

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

15. Field Trials in Butte County To evaluate fungicides and water repellants (oils and anti-transpirants)

16. Efficacy of Fungicides in Reducing Mandarin Rind Breakdown Butte Co. 2002 Check Topsin 75WP Abound 2F Pristine 38WG 0 20 40 60 80 100 2003 Check Abound 2F Topsin 75WP VaporGard Omni Oil Topsin 75WP+Oil 0 5 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.

17. Oct. Nov. Nov. Nov. Incidence of MRB (%)* Trt Rate (/A) 22 9 19 26 a Check --- --- --- --- a Abound 12.8oz @ --- @ --- b Vapor Gard 1gal @ @ --- @ b Vapor Gard 1gal @ --- --- --- b Omni Oil 6qt-0.75% @ @ --- @ b Omni Oil 6qt-0.75% @ --- --- --- VaporGard b 1 gal/6 lb @ --- --- --- /Nordox Protected --- --- --- --- --- ** 0 5 10 15 20 25 30 35 Effect of fungicides and water repellants on the incidence and severity of rind breakdown of mandarins in field trials Field trial, Butte Co. 2004

18. 2005 Season Efficacy of preharvest treatments in reducing MRB in California

19. 2005 Precipitation in Butte County….. Northern vs. Central California 35 Totals: Parlier, CA 27.5 mm 30 144.2 mm Durham, CA 25 20 Precipitation (mm) 15 10 5 0 11/3/2005 12/1/2005 12/8/2005 10/20/2005 10/27/2005 11/10/2005 11/17/2005 11/24/2005 12/15/2005 Date Data from CIMIS.

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

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

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

23. Joe Connell, Farm Advisor, Butte County 538-7201