Pre- and postharvest control strategies to prevent decay and meet quarantine requirements for Phytophthora brown rot

Transcription

1 Pre- nd posthrvest control strtegies to prevent decy nd meet qurntine requirements for Phytophthor brown rot Updtes on current disese mngement J. E. Adskveg Deprtment of Plnt Pthology nd Microbiology University of Cliforni Riverside, CA Phytophthor diseses of citrus ffect roots, tree trunks, fruit Helthy tree Foot rot & Gummosis Tree decline, diebck, yield reduction Brown rot Root rot 1

2 Phytophthor diseses of citrus ffect roots, tree trunks, fruit Minly 4 species of Phytophthor re involved: P. citrophthor P. prsitic (P. nicotine) P. syringe P. hibernlis These species my ll cuse fruit brown rot, but root rot nd gummosis re minly cused by P. citrophthor nd P. prsitic. Occurrence of the 4 species is sesonl: Winter: P. citrophthor, P. syringe, P. hibernlis Summer: P. prsitic Epidemiology of Phytophthor root rot Phytophthor root rot cuses slow decline of the tree. The disese destroys the feeder roots of susceptible rootstocks. The pthogen infects the root cortex, which turns soft nd seprtes from the stele. If the destruction of feeder roots occurs fster thn their regenertion, the uptke of wter nd nutrients will be severely limited nd stored energy reserves will be depleted. Disese symptoms re often difficult to distinguish from nemtode, slt, or flooding dmge; only lbortory nlysis cn provide positive identifiction. 2

3 Epidemiology of Phytophthor root rot Mostly cused by P. citrophthor nd P. prsitic Phytophthor species re present in most citrus groves. P. citrophthor: Active during cool sesons when citrus roots re inctive nd their resistnce to infection is low. P. prsitic: Active during wrm wether when roots re growing. Survivl of dverse conditions in the soil s persistent spores. Source of wter my be fctor for disese severity well wter vs. surfce wter (i.e., rivers) Chlmydospores of P. prsitic re survivl structures Citrus Brown Rot Species of Phytophthor involved: - P. citrophthor - P. prsitic (P. nicotine) - P. syringe - P. hibernlis Occur in ll growing regions of CA. P. citrophthor nd P. prsitic re considered most importnt. Losses re ssocited with periods of high rinfll. Other species re qurntine or potentil qurntine problems P. syringe, P. hibernlis 3

4 Citrus Brown Rot Symptoms nd Economic Impct Develops minly on mture fruit in the lower tree cnopy Olive-brown discolortion of the rind Distinctive pungent odor Fruit remin firm nd lethery, unless invded by secondry decy orgnisms. At high humidity, fruit become covered by delicte white growth of the fungus. The most serious spect: Fruit infected before hrvest my not show symptoms. If infected fruit get mixed with helthy fruit, the disese my spred quickly from fruit to fruit in storge nd during trnsit. Citrus brown rot: pre- nd posthrvest losses Citrus Brown Rot Economic Impct P. syringe recently hs become regultory issue in the exporttion of Cliforni ornge fruit to Chin - P. syringe hs been considered of limited distribution nd minor importnce s compred to P. citrophthor or P. prsitic. 4

5 Citrus Brown Rot Distribution of cusl pthogens Survey on the geogrphic distribution of Phytophthor species cusing brown rot of citrus. Isoltes re chrcterized using morphologicl nd moleculr methods. In winter smplings, we found P. citrophthor nd P. syringe. P. syringe my be more widely distributed thn previously thought. Oospore of P. syringe Sporngium of P. syringe Hyphl swellings of P. syringe Sporngi of P. citrophthor (no oospores re produced) Disese cycle of Phytophthor spp. The root rot nd brown rot phses re connected 18 h of wetness required for sporngi production nd zoospore relese. 3 h of wetness required for infection. Zoospores from sporngi on the ground my be splshed up onto lowhnging fruit nd the trunk. Inoculum levels nd wetness length re the most importnt predictors of brown rot epidemics. Smple P. prsitic July through September, P. citrophthor Jnury through Mrch. Phytophthor popultions >15 to propgules/g root zone soil my wrrnt tretment. 5

6 Wetness nd temperture effects on infection of Nvel ornges by P. citrophthor Zoospores encysted within n hour t incubtion t C. Germ tubes were observed fter 1 h. 9 h t 1 C 4 h t C 4 h t C Cyst Cyst Germ Tube Germ tube Infection hyph Infection hyph Appressorium Fruit inocultion studies t C: 1 h wetness - no disese 1.5 h wetness - 1% incidence 2 h wetness - 7% incidence Experiments with P. syringe re currently being done Mngement of Phytophthor Diseses P. citrophthor relesing zoospores Culturl prctices Resistnt rootstocks Plnting on berms for dequte dringe Avoid over-irrigtion Alternte side irrigtion Dringe tiles Skirting of trees Fumigtion Surfctnts Fungicides Prehrvest Posthrvest 6

7 Mngement of Phytophthor Diseses - Rootstocks Type Rootstock Root rot Gummosis Lemon Mcrophyll Tolernt Tolernt Rough lemon Susceptible Susceptible Volkmerin Susceptible Susceptible Yum ponderos Tolernt Tolernt Ornge Tiwnic Susceptible Tolernt Sour ornge Intermedite Tolernt Sweet ornge Susceptible Susceptible Trifolite Tolernt Tolernt Hybrids C-35 citrnge Tolernt Tolernt C-32 citrnge Tolernt Tolernt Crrizo citrnge Intermedite Tolernt Troyer citrnge Intermedite Tolernt Swingle Tolernt Tolernt Source: UC ANR Publiction Alternte Side Irrigtion to Control of Phytophthor Root Rot Single-line microsprinkler system A Alternting Irrigtion B Dul-line microsprinkler system b b Alternte row irrigtion 7

8 Mngement of Phytophthor root rot with chemicls Orchrd Evlution site of nd evlution soil ppliction of the efficcy of fungicides of & surfctnts for concentrtion mnging nd frequency of ppliction Phytophthor root rot Wter Ridomil 2E 1 mg/l Nid mg/l Nid 8

9 Tree excvtion nd determintion of root weight Control ppm root flush ppm every irrig. Ridomil Selected Fungicides with Activity Aginst Oomycetes Clss FRAC Common Nme Trget Appliction Inorgnic* M1 Coppers, Bordeux Folir Folir Phosphontes* 33 Fosetyl-Al, Folir, soil, Folir, soil phosphorous cid posthrvest Phenylmides* 4 Metlxyl, mefenoxm Folir, soil Soil, trunk QoIs* 11 Azoxystrobin, Folir, Folir fenmidone, others posthrvest Dimethomorph, CAAs mndipropmid**, Folir Posthrvest iprovlicrb Benzmides 43 Fluopicolide** Folir (soil) Folir (soil) Crbmtes 28 Propmocrb Folir, soil Folir, soil Piperidinyl thizole isoxzoline New group Oxthipiprolin Folir (soil) Folir (soil) Surfctnts*** --- Vrious Soil Soil Fungicide clsses evluted for root rot mngement * - Registrtion on tree crops including citrus. ** - Proposed to IR-4 for tree crops (e.g., citrus). *** - Soil mendment, not lbeled for disese control. 9

10 Trget sites of chemicls ctive ginst Phytophthor prsitic surfctnts, fenmidone phosphontes Zoospores phosphontes, mefenoxm, iprovlicrb Sporngi 2n Asexul 2n Mycelium Chlmydospores Sexul Oospores n+n n Sporngi mefenoxm phosphontes Trget sites of newer fungicides re currently being evluted. Effect of single soil ppliction of fungicides on root rot of citrus in greenhouse studies mefenoxm D fenmidon/iprovlicrb CD fenmidon C iprovlicrb BC propmcrb AB wter check A Incidence (%) Citrus seedlings were trnsplnted from flts into pet pots contining soil inoculted with chlmydospores ( 32/g soil). Fungicides were prepred in wter t concentrtion of 2 ppm nd pplied to seedlings ( ml/pot). Check plnts received ml wter. There were seven single-seedling replictes per tretment. The experiment begn in August 1 nd concluded 9 dys lter. Mefenoxm is highly effective, but resistnce occurs t mny loctions. New soil fungicides re currently being evluted in lrge-scle field study. 1

11 Conclusions Mngement of root rot Fungicides cn be effective ginst species of Phytophthor cusing citrus root rot in Cliforni - Mefenoxm ws the most effective fungicide. Citrus root rot ws effectively controlled in greenhouse nd field experiments. Phosphontes were lso very effective ginst citrus root rot. Efficcy of fenmidone, iprovlicrb, nd propmcrb ws lower nd thus, these fungicides were not developed for use on citrus. New fungicides re currently under investigtion. New fungicides for mngement of Phytophthor root rot Mndipropmid (evluted, but is plnned only for posthrvest pplictions) Fluopicolide Oxthipiprolin A field tril with nvel ornge on Crrizo rootstock ws estblished t UC Riverside in Sept

12 New tretments for brown rot nd root rot In vitro fungicide sensitivities ginst mycelil growth Fungicide FRAC P. prsitic (ppm) (16 isoltes) P. syringe (ppm) (28 isoltes) Mefenoxm Fluopicolide Mndipropmid Oxthipiprolin New*.4.11 <.1 Mndipropmid nd oxthipiprolin re most effective Oxthipiprolin: new clss - piperidinyl thizole isoxzoline Additionl isoltes nd isoltes of P. citrophthor re being evluted Toxicity ginst other stges in the life cycle (zoospore production, cyst germintion, oospore production) re lso being evluted In vitro ctivity of potssium phosphite ginst P. citrophthor nd P. syringe P. citrophthor ppm P. citrophthor1 ppm P. syringe ppm P. syringe 1 ppm Three isoltes of ech species. 12

13 Regressions of mycelil growth inhibition of P. citrophthor nd P. syringe on concentrtion of potssium phosphite Inhibition of mycelil growth (%) 1 1 P. citrophthor P. syringe Regressions y = x R 2 =.92, P <.1 y = x R 2 =.96, P < log1 concentrtion (mg/l) Adskveg nd Forster, 14. Concentrtions of potssium phosphite were from to mg/l. Regressions were performed using nlysis of vrince procedures. Mngement of Phytophthor Brown Rot - Prehrvest Fungicide Sprys - 13

14 Mngement of Phytophthor Brown Rot - Prehrvest Fungicide Sprys - Current guidelines: - One spry of copper fungicide between October nd December before or just fter the first rin. - Apply t -7 gl/a. - If frequent nd high rinfll fter the first ppliction, repet pplictions in Jnury or Februry. - Spry the skirts to bout 4 feet bove ground; whole tree pplictions my be necessry for some vrieties or in orchrds with history of the disese. - Sprying the ground underneth the trees my lso reduce brown rot infections. Mngement of Phytophthor Brown Rot - Prehrvest fungicide sprys - Most effective orchrd sprys: Bordeux mixture (copper sulfte + lime) with.6 to.8 lb of metllic copper/1 gl. Neutrl (fixed) coppers (copper hydroxide, copper oxide) Phosphontes (e.g., fosetyl-l - Aliette 5 lb/a, potssium phosphite - Prophyt 4 pints/a, etc.) re systemic nd provide effective control when pplied up to 5 weeks prior to infection. Phenylmides (e.g., mefenoxm) Ridomil Gold.5-3 qt/a pplied to soil 14

15 Selected Fungicides with Activity Aginst Oomycetes Clss FRAC Common Nme Trget Appliction Inorgnic* M1 Coppers, Bordeux Folir Folir Phosphontes* 33 Fosetyl-Al, Folir, soil, Folir, soil phosphorous cid posthrvest Phenylmides* 4 Metlxyl, mefenoxm Folir, soil Soil, trunk QoIs* 11 Azoxystrobin, Folir, Folir fenmidone, others posthrvest Dimethomorph, CAAs mndipropmid**, Folir Posthrvest iprovlicrb Benzmides 43 Fluopicolide** Folir (soil) Folir (soil) Crbmtes 28 Propmocrb Folir, soil Folir, soil Piperidinyl thizole isoxzoline New group Oxthipiprolin Folir (soil) Folir (soil) Surfctnts*** --- Vrious Soil Soil Fungicide clsses evluted for brown rot mngement * - Includes registrtion on tree crops including citrus. ** - Proposed to IR-4 for tree crops (e.g., citrus). *** - Soil mendment, not lbeled for disese control. New prehrvest tretments for control of brown rot cused by Phytophthor spp. Control Bdge 7 pts + Lime 3.5 lb Fruit hrvested 6 weeks fter field tretment nd inoculted with P. citrophthor Revus 8 fl oz Oxthipiproline 4.8 fl oz 15

16 Persistence of new prehrvest tretments for control of brown rot cused by Phytophthor spp Control Presidio 4 fl oz Prophyt 64 fl oz Bdge SC 128 fl oz + Lime 16 l Mndipropmid 8 fl oz 2 wk 3 wk 4 wk 5 wk 6 wk 7 wk 8 wk Field pplictions UC Riverside Note: Presidio ws not evluted fter 4 wks. Revus (Mndipropmid), Prophyt (Phosphorous cid), nd Bdge-Lime (copper oxychloride- copper hydroxide) were very effective when fruit were hrvested 2 weeks fter ppliction. After 21 dys, Presidio ws no longer effective, wheres efficcy of Prophyt ws reduced fter 4 weeks. Copper effective for c. 6 wk; wheres Revus ws still very effective for 8 wk. Temperture (C), Precip. (mm) New prehrvest tretments for brown rot - 14 Temporl efficcy of prehrvest tretments to nvel ornges 1/1/14 Brown rot incidence (%) 1 Control Kocide lb + Zinc 4.5 lb + Lime 1/8/14 1 1/15/14 1 1/22/14 1 1/29/14 2/5/14 Presidio 4 fl oz Prophyt 64 fl oz 1 2/12/14 1 2/19/14 1 A941A 4.8 fl oz oxthipiproline Tril t Kerney Ag Center Tretments pplied t gl/a on Jn. 3, 14. Fruit were hrvested weekly for 8 weeks nd inoculted with P. citrophthor. Totl precipittion during tril period 55 mm. 2/26/14 1 3/5/14 16

17 Avg. Temperture(C), Precip. (mm) New prehrvest tretments for brown rot - 14 Temporl efficcy of prehrvest tretments to nvel ornges Inc. of brown rot 2/1/14 1 Control Bdge 7 pt + Lime 3.5 lb 2/8/14 2/15/14 2/22/14 Presidio 4 fl oz Prophyt 64 fl oz P. citroph. P. syr. P. citroph. P. citroph. P. citroph. Tril t UC Riverside Tretments pplied t gl/a on Feb. 3, 14. Fruit were hrvested t selected intervls nd inoculted Totl precipittion during tril period 41.9 mm. 3/1/14 Not done 3/8/14 A18269A oxthipiprolin 4.8 fl oz Revus 8 fl oz 3/15/14 Not done Not done 3/22/14 3/29/14 Mngement of Phytophthor Brown Rot - Posthrvest Fungicide Tretments - 17

18 New posthrvest tretments for control of brown rot cused by Phytophthor spp. Lbortory studies: Tretment of fruit 15 h fter inocultion Control ProPhyt 12 ppm New posthrvest tretments for control of brown rot cused by P. citrophthor Post-infection ctivity Pre-infection ctivity Wter (control) Potssium phosphite 63 mg/l b bc Potssium phosphite 12 mg/l b cd Mndipropmid 3 mg/l Fluopicolide 3 mg/l Azoxystrobin mg/l d cd b 1 1 Incidence of brown rot (%) Post infection ctivity: Dip tretments 15 h fter inocultion Pre infection ctivity: Inocultion 6 h fter tretment Azoxystrobin, mndipropmid (Revus), fluopicolide (Presidio), nd potssium phosphite (Prophyt, Fungiphite) were highly effective s preinfection tretments Only potssium phosphite ws effective s post-infection tretment. Potssium phosphite ws lso highly effective ginst brown rot cused by P. syringe nd P. hibernlis in other studies. 18

19 Potssium phosphite nd het tretments for control of brown rot cused by P. citrophthor in the lbortory Chemicl Aqueous dip Temperture Wter (control) mbient --- Fruit coting spry Wter 56C --- Imzlil 1 mg/l mbient Imzlil 1 mg/l + TBZ 35 mg/l Potssium phosphite mg/l mbient --- b bc Potssium phosphite mg/l Potssium phosphite mg/l Potssium phosphite mg/l + imzlil 1 mg/l Potssium phosphite mg/l + imzlil 1 mg/l mbient 56C mbient 56C Imzlil 1 mg/l + TBZ 35 mg/l Imzlil 1 mg/l + TBZ 35 mg/l Imzlil 1 mg/l + TBZ 35 mg/l Imzlil 1 mg/l + TBZ 35 mg/l 15-sec dip tretments done h fter inocultion. 56C = 133F d cd b b 1 Incidence of brown rot (%) Slight negtive interction between K-phosphite nd fruit coting, but tretment t higher temperture ws effective. p p brown rot cused by P. citrophthor in the lbortory Tretment temperture mbient nd 1F = C Tretment temperture mbient nd 13F = 54C Aqueous dip 15 sec Dip temperture Wx spry Wter mbient --- K- phosphite ppm mbient --- K- phosphite ppm + Imzl. 1 ppm K- phosphite ppm + Imzl. 1 ppm Aqueous dip 15 sec mbient 1F Dip temperture Imzl 1 ppm + TBZ 35 ppm Imzl 1 ppm + TBZ 35 ppm Wx spry Wter mbient --- Wter 13F --- Incidence of brown rot (%) c bc b 1 Incidence of brown rot (%) b K- phosphite ppm + Imzl. 1 ppm 13F Lb studies, 15-sec dip tretments -24 h fter inocultion. Imzl 1 ppm + TBZ 35 ppm c 1 Tretments t 1F were consistently highly effective. Tretments t 13F were vrible in efficcy. 19

20 Evlution of posthrvest tretments in commercil pckinghouse for control of brown rot of Nvel ornges Study 1 Control (untreted) Tretments Imzlil 1 mg/l b t 55C 131F, 11 sec Imzlil 1 mg/l c + potssium phosphite 1 mg/l Incidence of brown rot (%) Fruit were inoculted with zoospores of Phytophthor citrophthor nd treted fter h in heted (verge temperture 55º C) flooder for pproximtely 11 sec. This ws followed by spry ppliction with 1 mg/l imzlil nd 3 mg/l thibendzole (TBZ) in crnub-bsed pcking fruit coting. Fruit were incubted for 8 dys t C nd then evluted for the incidence of brown rot. Mngement of citrus brown rot cused by P. citrophthor on inoculted nvel ornges in commercil pckinghouse Study 2 Control Imzlil 1 ppm Imzlil-Potssium Phosphite 1/ ppm b b Imzlil-Potssium Phosphite 1/ ppm Tretments t 52-58C F, 11 sec c Incidence of brown rot (%) Tretments were pplied in heted flooder t F. Ech tretment hd 1 fruit. Fruit were evluted fter two weeks of incubtion t 68F (C). Percent control ws bsed on the reduction of brown rot incidence of ech tretment s compred to the control tretment.

21 New posthrvest tretments for Phytophthor brown rot Brown rot studies with inoculted fruit: 15-sec wter dips t 1F were highly effective 15-sec wter dips t 13F were modertely nd inconsistently effective 15-sec dips with K-phosphite t ppm were highly effective Negtive interction with imzlil nd subsequent ppliction of fruit coting Heted K-phosphite tretments re the best option: contct ctivity nd residul ctivity. Summry: New tretments for Phytophthor brown rot of citrus Potssium phosphite is highly effective ginst Phytophthor brown rot nd cn be used prehrvest nd posthrvest to prevent decy. Severl phosphite products re registered. They hve exempt sttus in the US. IR-4 residue studies re being done to obtin interntionl MRLs/FAT As lwys, check MRL dtbses for the limits of specific export country. (Some countries consider phosphites s pesticides). The posthrvest fungicide Grdute A+ cn lso be used s protective tretment to prevent the spred of brown rot. Additionl mterils (mndipropmid, fluopicolide, oxthipipropline) hve been identified for pre- or posthrvest use nd re considered for registrtion. 21

22 Implementtion of Results by Industry Two pproches to solving Phytophthor brown rot for ornge export to Chin - Potssium phosphite posthrvest tretments Hot wter posthrvest tretments Prehrvest Mngement Prctices Skirting Folir nd fruit pplictions of copper Development of new fungicides for seson-long control Mnging soil popultions of pthogens nd root rot control with fungicides (mefenoxm, phosphontes, nd new fungicides) Results will hve to be pproved by APHIS nd Chin? Systems pproch llows for chieving 99% control (Probit 9 >99.9% is not requirement for plnt diseses) Questions? 22

23 Updte on posthrvest ctivities for decy mngement of citrus Evlution of new chemistries Resistnce monitoring Development of nti-resistnce strtegies Supporting current registrtions Developing new registrtions nd MRL/FATs in interntionl mrkets Posthrvest fungicides for citrus in the US Phenols Sodium ortho-phenyl phente (SOPP) 193s Phenylpyrroles Fludioxonil (Grdute) 6 Anilinopyrimidines Benzimidzoles Thibendzole (TBZ) 197s Strobilurins (QoIs) Azoxystrobin (Diplom) Pyrimethnil Potssium (Penbotec) Reduced risk fungicides Phosphite (Prophyt, Kphos) DMI-imidzoles Imzlil DMI-trizoles Propiconzole (Mentor) 1 Phosphontes New 12 EXP-13 19s New requirements Fungicide with resistnce in Penicillium spp. popultions Gol is to prevent resistnce to fludioxonil nd zoxystrobin nd to define usge pttern for fungicides with resistnce. New mixture prtners for other fungicides 23

24 Regultory sttus of posthrvest fungicides Compound Clss* FRAC No.* MRLs/FAT** Field Resistnce Azoxystrobin QoI (Strobilurin) 11 Mny/Yes No Fludioxonil Phenylpyrrole 12 Mny/Yes No Imzlil DMI Imidzole 3 Mny/Yes Yes Propiconzole DMI Trizole 3 Some/No Yes Pyrimethnil Anilinopyrimidines 9 Mny/Yes Yes TBZ MBC 1 Mny/Yes Yes Imzlil is still highly needed in citrus IPM progrms: Hs different mode of ction from other registered fungicides, except propiconzole Cn be used in rottions nd mixtures resistnce mngement Hs interntionl MRLs nd FAT Resistnt popultions of Penicillium spp. re less fit. Inevitbly imzlil my be cnceled if it stys on the Prop 65 list. Questions? 24