Phytophthora Brown rot of Citrus - A Quarantine Issue for Fruit Exports to China - - GAPS for Managing Brown Rot -

Transcription

1 Phytophthora Brown rot of Citrus - A Quarantine Issue for Fruit Exports to China - - GAPS for Managing Brown Rot - J. E. Adaskaveg University of California, Riverside Cooperating H. Forster and W. Hao University of California, Riverside

2 Phytophthora diseases of citrus trees Healthy tree Foot rot & Gummosis Historically primary species: P. citrophthora - fall, winter, spring P. parasitica (P. nicotianae) - summer Tree decline, dieback, yield reduction Root rot

3 Citrus Brown Rot Causal pathogens: species of Phytophthora - P. citrophthora - P. syringae - P. parasitica (P. nicotianae) - P. hibernalis Occur in all growing regions in CA. P. citrophthora is considered most important. The four species also cause Phytophthora root rot, foot rot, and gummosis. Losses are associated with periods of high rainfall.

4 Citrus Brown Rot Symptoms and Economic Impact Develops mainly on mature fruit in the lower tree canopy Olive-brown discoloration of the rind Distinctive pungent odor Fruit remain firm and leathery, unless invaded by secondary decay organisms. At high humidity, fruit become covered by white growth of the fungus. Fruit infected before harvest may not show symptoms. If infected fruit get mixed with healthy fruit, the disease may spread quickly from fruit to fruit in storage and during transit. Citrus brown rot: pre- and postharvest losses

5 Phytophthora diseases of citrus occur throughout California Historical distribution of Phytophthora diseases of citrus in California Survey area Brown rot caused by Phytophthora spp. infection through intact tissue.

6 Disease cycle of Phytophthora species 18 h of wetness required for sporangia production and zoospore release. 3 h of wetness required for infection. Zoospores produced in sporangia on the ground may be splashed up onto low-hanging fruit and the trunk. Brown rot mainly develops on fruit growing near the ground. Continuous rainy periods are important in forecasting brown rot epidemics. Inoculum levels in orchards determines severity of infections.

7 Wetness and temperature effects on infection of Navel oranges by P. citrophthora Zoospores encysted within an hour at incubation at 20C. Germ tubes were observed after 1 h. 9 hr at 10 C 4 hr at 20 C 4 hr at 20 C Cyst Germ Tube Cyst Germ tube Infection hypha Infection hypha Appressorium Fruit inoculation studies at 20C: 1 h wetness - no disease 1.5 h wetness - 10% incidence 2 h wetness - 70% incidence Experiments with P. syringae pending

8 Phytophthora syringae is an ongoing regulatory issue in the exportation of California orange fruit to China.

9 Summary Part I- Phytophthora brown rot in CA P. citrophthora, P. syringae, P. hibernalis, and P. parasitica are responsible for brown rot of citrus in California. P. citrophthora and P. syringae are most common. Copper is the cornerstone for disease management Phosphonates are effective as pre- and postharvest treatments for the management of brown rot but cannot be used because there are no MRLs in China. New fungicides are in development. Management practices historically included preharvest copper applications (postharvest applications with phosphonates are proposed). Integrated strategies required to open China market.

10 Industry s response Improved understanding of Phytophthora root rot and brown rot: Species: P. syringae, potentially P. hibernalis (quarantine reasons) New product registrations for management of brown rot & root rot Characterize new treatments - guidelines for usage GAPs prepared for industry-wide meetings - Guidelines to manage Phytophthora brown rot Information on how to meet Chinese export agreement (2-yr pilot program) Management: Efficacy of preharvest cultural practices and preand postharvest chemical treatments is cumulative and warrants a systems approach for control of Phytophthora brown rot of citrus.

11 Good Agricultural practices (GAPs) for the Management of Phytophthora Brown Rot content/uploads/jea-brown-rot-gaps- Citrus20141.pdf

12 Management of Phytophthora Diseases P. citrophthora releasing zoospores Cultural practices Resistant rootstocks Planting on berms for adequate drainage Avoid over-irrigation Alternate side irrigation Drainage tiles Skirting of trees 24 in Fumigation Surfactants Fungicides Preharvest Postharvest

13 Management of Phytophthora Diseases - Rootstocks Type Rootstock Root rot Gummosis Lemon Macrophylla Tolerant Tolerant Rough lemon Susceptible Susceptible Volkameriana Susceptible Susceptible Yuma ponderosa Tolerant Tolerant Orange Taiwanica Susceptible Tolerant Sour orange Intermediate Tolerant Sweet orange Susceptible Susceptible Trifoliate Tolerant Tolerant Hybrids C-35 citrange Tolerant Tolerant C-32 citrange Tolerant Tolerant Carrizo citrange Intermediate Tolerant Troyer citrange Intermediate Tolerant Swingle Tolerant Tolerant Source: UC ANR Publication 21477

14 Alternate Side Irrigation to Control of Phytophthora Root Rot Single-line microsprinkler system A Alternating Irrigation B Dual-line microsprinkler system

15 Management of Phytophthora Brown Rot - Preharvest Fungicide Sprays - Current guidelines: - First spray of copper fungicide between October and December before or just after the first rain. - Apply at gal/a (lower 4 ft of tree > whole tree). - If frequent and high rainfall occurs after the first application, repeat applications in January or February. - Spray the skirts to about 4 feet above ground; whole tree applications may be necessary for some varieties or in orchards with a history of the disease or for management of P. hibernalis. - Spraying the ground underneath the trees may also reduce brown rot infections.

16 Objective: Persistence of new preharvest treatments for control of brown rot caused by Phytophthora spp. 100 Control 80 Presidio 4 fl oz Prophyt 64 fl oz 60 Badge SC 128 fl oz + Lime 16 l Mandipropamid 8 fl oz 40 Field applications 20 0 Note: Presidio was not evaluated after 4 wks. 2 wk 3 wk 4 wk 5 wk 6 wk 7 wk 8 wk Revus (Mandipropamid), Prophyt (phosphorous acid), and Badge-Lime (copper oxychloride- copper hydroxide) were very effective when fruit were harvested 2 wk after application. After 3 wk, Presidio was no longer effective, efficacy of Prophyt was reduced after 4 wk. Copper effective for ca. 6 wk; whereas Revus was still very effective for 8 wk.

17 Management of Phytophthora Brown Rot - Preharvest fungicide sprays - Most effective orchard sprays: Bordeaux mixture (copper sulfate + lime) with 1.6 to 2.4 lb of metallic copper/a. ( MCE/100 gal) Neutral (fixed) coppers (copper hydroxide, copper oxide, ) see label ( MCE/A) Phenylamides (e.g., mefenoxam) Ridomil Gold qt/a applied to soil Phosphonates (e.g., fosetyl-al - Aliette 5 lb/a, potassium phosphite - Prophyt 4 pints/a, etc.) Not approved in China.

18 Recommendations for copper sprays Always check labels for rates. TABLE 1 First Application Season Zinc-Copper-Lime Applications Fixed coppers (e.g., copper hydroxide and copper oxide) Application Volume Metallic Zinc/100 gal Metallic Copper/100 gal Hydrated Lime/100 gal 200 gal/a lb lb lb 400 gal/a lb lb lb 600 gal/a lb lb lb Total* lb/a * - If brown rot was observed in a grower lot last season, use a higher rate of each spray component within the range provided. ** - Note that other fungicides can be used in rotation with copper. TABLE 2 First Application Season Zinc-Copper Bordeaux Applications (Zinc monohydrate + Copper pentasulfate) Application Volume Metallic Zinc/100 gal Metallic Copper/100 gal Hydrated Lime/100 gal 200 gal/a 1.65 lb lb lb 400 gal/a 0.83 lb lb 5-17 lb 600 gal/a 0.55 lb lb lb Total* lb/a * - If brown rot was observed in a grower lot last season, use a higher rate of each spray component within the range provided. ** - Note that other fungicides can be used in rotation with copper.

19 Models for industry-wide forecasting of brown rot and timing of fungicide applications 1. Prediction of infection periods Numerical risk model for forecasting brown rot caused by P. syringae Wetness period (h) Temperature range ( F) Temperature range ( C) < >25 <41 < > >50-68 > >68-77 > >77 > Numerical risk model for forecasting brown rot caused by Phytophthora syringae based on cardinal temperatures, temperature range for growth, and wetness periods.

20 Models for industry-wide forecasting of brown rot and timing of fungicide applications 2. Persistence of copper applications Agroclimate - Citrus Copper Application Scheduler (A) and overview (B). Weather station or uploaded weather data (C) can be used for different citrus crops with their bloom date (D). Application attributes are entered for dates of application, amount of copper, volume of application (E).

21 Models for industry-wide forecasting of brown rot and timing of fungicide applications 3. Risk assessment of orchards Risk categories for monitoring orchards for Phytophthora brown rot based on field surveys of 50 orchards Rating Category China Export 1 Low risk: <10 fruit with brown rot per acre Shipped 2 Moderate risk: fruit with brown rot per acre Caution if shipping 3 High risk: >20 fruit with brown rot per acre Ship to other markets Field monitoring - monthly or within 14 days after every major rainfall, and one week before each harvest.

22 Summary Part II - Implementation of Agreement Two approaches to solving Phytophthora brown rot for orange export to China Preharvest management practices Tree skirting (UC Guidelines - 24 in) (61 cm); Fruit harvested above 20 in (50 cm) are sent to China (lower fruit sent to other markets) Foliar and fruit applications with copper (1 st application mand.) Development of new fungicides for season-long control Managing soil populations of pathogens and root rot control with fungicides (e.g., mefenoxam), tolerant rootstocks Monitoring orchards and forecasting environmental conditions conducive for disease and removal of copper Postharvest treatment Future registration in China Potassium phosphite (Not available for this season) New guidelines currently being discussed by APHIS (USA) and AQSIQ (China)

23 Postharvest Fungicides A. Potassium phosphite (Not available) Potassium phosphite is registered for postharvest use on domestic fruit and for countries that have MRLs for postharvest usage. China is currently registering potassium phosphite for postharvest use. At this time, fruit should NOT be treated postharvest with potassium phosphite or other phosphonate fungicide. B. Fruit may be treated with registered postharvest fungicides for management of green and blue mold (Penicillium decays). Aqueous treatments of imazalil (e.g., Fungaflor, Deccocil, Freshgard, etc.), pyrimethanil (Penbotec), sodium bicarbonate, TBZ (Alumni), or other registered fungicide should be applied prior to a fruit coating or wax. Fungicides including imazalil, pyrimethanil, and/or TBZ may also be applied in a fruit coating. Currently, MRLs for azoxystrobin and fludioxonil have not been established in China. China MRLs Crop Imazalil Pyrimethanil TBZ Orange Lemon

24 Postharvest Heated-Water Treatments Reduction in decay incidence (%) y = x r 2 = P < Temperature ( C/F) Note: Dip temperatures are for fungicide reservoir solutions. Dip times were 15 sec. Fawcett (1936) - 2- min dips at 49C (30 h after inoculation) Klotz and DeWolfe (1961) - 4-min dips at 48C after 48 h at 25C or 60 h at 12C after inoculation. Adaskaveg et al. (2015) linear response for reduction in decay from 50 to 60C (24 h after inoculation at 20C). Fig. to right

25 Postharvest Heated-Phosphite Solutions Reduction in brown rot incid. (%) K-phosphite - ambient Imazalil+K-phosphite - heated y = x, r 2 = 0.95, P < 0.01 y = x, r 2 = 0.94, P < Treatment time after inoculation (h) Adaskaveg et al. (2015) linear response for reduction in decay using heated or ambient solutions of phosphite from 24 to 48 h after inoculation at 20C). Fig. to right

26 Regulatory Aspects Grading - All fruit destined for China should be graded. 1. Fruit with symptoms of brown rot should be identified and reported to packinghouse managers. 2. If fruit lots are confirmed to have brown rot, the lots should not be further considered for export to China. Phytosanitary inspection prior to export 1. APHIS will apply a 0% tolerance for any type of decay during inspection. Any grower lot displaying decay of any kind (brown rot, green mold, sour rot, etc.) will be rejected and not certified. 2. All fruit lots that pass inspection shall be provided with a Phytosanitary Certificate and state the additional declaration: This shipment complies with The Protocol of Phytosanitary Requirements of California Citrus exported to China and Supplementary Inspection and Quarantine Requirements for California Citrus to be Exported to China.

27 Good Agricultural practices (GAPs) for the Management of Phytophthora Brown Rot content/uploads/jea-brown-rot-gaps- Citrus20141.pdf

28 GAPs - Fungicides Fungicide treatments for brown rot control: 1) Fungicide treatments can protect fruit from infection by Phytophthora spp. Multiple treatments may have to be applied during the harvest season. 2) The first protective application is mandatory and must be a registered copper compound and must be done after the first rain to all citrus planned for exportation to China. October 15 and November 30. 3) Second and third applications may be needed 4) Registered fungicides include fixed coppers, Bordeaux mixtures, and mefenoxam (this latter fungicide is used as a soil treatment) can be used. Phosphites not allowed at this time. 5) Foliar applications of copper sprays - effective for ca. 6 weeks. 6) Pesticide Use Reports should be available.

29 GAPs Timing of Fungicides and Monitoring Timing of additional fungicide applications: 1) Based on rainfall and when copper residues are significantly depleted. 2) Based on empirical forecasting model - numerical risk based on cardinal temperatures (i.e., minimum, optimum, and maximum temperatures) and wetness periods for growth and sporulation of P. syringae. Monitoring guidelines: 1) All grower lots must be field scouted for brown rotted fruit. 2) Risk assessment: a)low risk: <10 diseased fruit/a OK to ship to China b)moderate risk: diseased fruit/a - Caution in shipping c)high risk: >20 diseased fruit/a Do not ship to China 3) Frequency Monthly or within 14 days after rainfall or 7 days before harvest.

30 Potential Changes for Next Season Whole-tree fungicide applications - Phytophthora hibernalis detected - second quarantined pathogen detected along with P. syringae. Stricter requirements Documentation (checklists & records: orchard, spray, harvest, etc.) Tree Skirting Harvesting and segregation of fruit (low fruit) Monitoring, sampling, and certification Diseased fruit vs. soil? Postharvest heated water treatments?

31 Questions?