Controlling Root Rots

Controlling Root RotsJim DownerUniversity of California Cooperative ExtensionVentura County805-645-1458ajdowner@ucdavis.eduhttp://ceventura.ucdavis.edu

Why Root Rots• Destructive to a wide host range of plants– All plants are susceptible to some kind of rootrot• Economic: Cause large $$ lossessometimes resulting in complete loss ofcrops• Widespread: they are everywhere• Many organisms• Also can be abiotic

Causes of Root Rot• Water Molds (Oomycetes)– Pythium, Phytophthora,• Basidiomycetes– Ganoderma, Armillaria, Omphalotus, Oxyporus,Rhizoctonia• Ascomycetes– Rossalinia necatrix• Deuteromycetes– Fusarium and Fusarium/nematode complexes• Anoxic or Hypoxic soil conditions– Flooding, natural gas leak in soil

Root Rots• Armillaria mellea:Oak Root Fungus• Phytophthora spp.Various root rots• Anoxic conditions– Flooding– Natural Gas Leakage

Phytophthora Life History• Mycelium– hyphae• Zoosporangia– Zoospores----->Cysts– Zoosporangia– hyphae• Chlamydospores• Oospores– A1 and A2 mating types

Interrupt the Phytophthora lifecycle

Chlamydospores• Long-term survival insoil aschlamydospores oroospores in old rootpieces.• Chlamydosporesgerminate to formmycelium andsporangia

ZoosporesCysts• Zoospores will encyston roots in the zoneof elongation “enmasse”

Cysts germinate and then infect afterpenetration of the root

Diagnosis

Roots• Roots are often dark ormelanized. Melanin isa protective chemicalthat reduces microbialattack• Annual emergence ofyoung roots indicatestheir health• “Skinning” the root witha pocket knife willassure you that theyare not decayed.Roots of Prunusspp.

Some roots are so black they lookdecayed

Healthy vs. Not

Most Roots are mycorrhizal• Mycorrhizal roots arestubby and are oftenprolific• Some mycorrhizalroots may be swollenor appear to becovered in fungalmycelium.Gingko biloba

PhytophthoraWhat is it?• A microscopic water “mold”• A member of the Oomycetes• Not a fungus• Now considered more closely related toalgae• A genus name. The genus contains wellover 100 spp.• A worldwide organism. It occurs on everycontinent

Diagnosis: symptoms• Wilt whole plant death• Yellowing• Dieback at the top of the tree/shrub• Cankers– Oxidized tissue– Spreading above ground• Feeder root rot

Avocado Root Rot

• Bleeding exudates onthe woody stem oftrees is a hallmarksymptom ofPhytophthorainfections.Bleeding

Phytophthora: symptoms

Phytophthora:symptoms

Ficus• Thinning of foliage isreally lack ofregrowth. Canopyvigor is severelycompromised.

Damages many ornamental trees

Note pink rot pathogensporulating on Phytopthora killedtissuesPhytophthora is an important palmtree killing pathogen

Palm Root RotPhytophthora nicotianeae

Disease predisposing factors• Excess moisture• Planting too deep– Backfill over the crown• Salinity• Compaction

Flooding is deadly if Phytophthora is present in the soil

Planting Too Deep• Almost always leadsto problems/death ofthe plant• Associated withPhytophthora collarrots• “Kiss of death” fornative plants

The vascular cambium• A meristematic tissue• Subject to pathogenicattack• One cell layer thickVascular cambium

Stem/Root intersection• Crown of the tree• A metabolic region• Physiologicallysensitive to theenvironment

• Backfill surrounding atree can havedisastrous or noeffects at all!Backfill

Anoxic root rots• Due to rootsuffocation– Excess water– Natural gassuffocation– Compacted soils

Soil Salinity

The toxic proportion• >1 ppm boron• >100 ppm Na or Cl• >1000 ppm TDSFrom Dr. Ben Faber, University of California Cooperative Extension, Ventura, CA

Soil Composition• Pores• Water• Soils• Air• Biology

Soil Structure• Soil particles combine to form aggregates

Earth transport + compaction

Methods and Mechanisms ofPhytophthora control• Fungicides• Cultural controls• Biological controls• Resistance• Integrated management

Gypsum MulchesProvide a slow release Ca ++sourceWill not harm avocadorootsWill harm Phytophthorapropagules.Provides control equivalentto fungicides in some cases

Zoospore motilityCalcium at 1mM concentrations reducesthe ability of the zoospores to swimUni-directionally. Disrupted swimmingpatterns prevent the spores from findinghost roots.

Zoospore encystmentHigh calcium levels causeencystment of zoospores.Encystment must occur onroots for an infection to occurIf zoospores encyst beforereaching roots they areunableto infect and will die.

Calcium control• Calcium supplied as gypsum• Applied to young trees at 15#/treeannually.• Gypsum applied as a mulch and leachedinto the soil profile or over organic woodchip mulches.

Phos. Acids• Phosphorus acids have become popular“fertilizers” for control of root rot in manycropping and ornamental plant growingareas• Are they all alike?• How do they compare to Aliette for root rotcontrol?

P. Cinnamomi control withphosphorus acidsUninoculated control Inoculated control Fosfite drench

Effect of various phosphorus acidson root rot control.3025weights (g)20151050rootsshootsPhosguardFosphyteNutriphyteFormula 1Alietteinoc +inoc 1K-fight

Fungicides• fosetyl-Al Aliette• mefenoxam Subdue Maxx• azoxystrobin Heritage• pyraclostrobin Insignia• cyazofamid Segway• propamocarb Banol, Previcur• etridiazole Terrazole• dimethomorph Stature DM• captan Captan• fluoxaastrobin Disarm• fenamidone Reason (vegies)

Other fungicides/agents• Phosphorus acids– Fosfite, Agrifos, Alude, Vital, Profos, K-fightetc.• Actinovate• Muscodor albus• Silicone (Monterey Chemical)• Gypsum

Mulch-hugger!

Effects of organic mulches• Soil physical changes– Infiltration, porosity• Mycoflora changes– Antagonists, hyperparasites• Changes in soil enzyme levels

The canopy of the tree should be withoutdefect and covered continuously withfoliage.

The rhizosphere• As a concept it variesdepending on howyou study it.• From 10um to a fewmm from the root• The biology andchemistry near theroot are very differentthan that of the bulksoil

Mulch Transect StudiesSurface ofmulchMid mulchInterface0-7.5 cm7.5-15cm

Soil Fungi

Organisms seen in MulchesDeutermycotinaabundant sporesBasidiomycotinaabundant biomassPhanerochaetechrysorhizaCeraceomycestessulatus

Mulch full of fungi

• Trees produceabundant roots inmulch layers• These roots aregenerally free ofPhytophthora.• Mulch layers arewhere cellulaseenzyme levels arehighest.Roots

Organic Matter: Benefits•Many mulch fungi are hyperparasites.•Trichoderma, Gliocladium, Pennicillium etc.

Enzyme activities in transectprofilesurfaceSample depthmidmulchinteface7.515cmCMCase-soilCMCase-mulchinfections0 2 4 6enzyme activities8mg reducing sugars/g soil/h

Enzyme meltdownCellulaseNo enzymes present

Mulch FungiCeraceomycestessulatusContainer study of various mulch fungi on sporedevelopment of P. cinnamomi.

Response of P. cinnamomi to mulch andand cellulase producing decay fungienzyme activity (x100)Chlamydospors/mg mycelium8007006005004003002001000bno mulchChlamydosporesbmulchcellulaseamulch +Ceraceomyces

Cellulase effects onZoosporangia/spore productionZoosporania/spores/ml120100806040200ZoosporangiaZoosporesObviousdifferencesignificantaccordingtoTukey’sHSD P=.050 0.1 1 10 50 100Enzyme Concentration (units/ml)

Mulch effects• Mulches provide the fungi necessary tocreate an environment destructive toPhytophthora.• This is due to both biological control viahyperparasites and enzymatic degradationof the the pathogen in the mulch layers.

Integrated Control• Use all the methods discussed today– Mulching– Fungicides– Planting on mounds (berms)– Water management– Resistance

Conclusions• Organic mulches probably have variedroles in the suppression of diseases in soilParasitism, enzymes and soil modification.• Phosphorus acids are effective but alike• Calcium ion can be used as therapy