VEGEnotesYour levy @ workControl of Sclerotinia diseasesSclerotinia diseases cause major loss in manyhorticultural crops (e.g. lettuce, beans, carrots,brassicas and peas). Intense cropping and theuse of Sclerotinia susceptible crops in rotationshave led to a build up of Sclerotinia in soil.There are new control options that have thepotential to contribute to, when integrated withother control measures, improved and sustainablecontrol of Sclerotinia lettuce drop, and otherdiseases caused by S. minor. These optionsinclude:• non-chemical controls (e.g. biological controlagents, biofumigant rotation crops)• cultural strategies (e.g. rotation crops tolerantto Sclerotinia infection)• procymidone, while an effective fungicide, hasrecently been withdrawn from use. Boscalid(Filan) is a suitable alternativeThere are two species of Sclerotinia that causeLettuce drop.• S. minor usually infects through mycelium thatcomes in contact with lower leaves and stems.On rare occassions it also produces aerial spores.• S. sclerotiorum usually infects through aerialspores landing on flowers and senescent ordamaged tissues. The fungus spreads fromthese infected flowers or tissues to healthy leavesor stems. Sclerotia of S. Sclerotiorum can alsoproduce mycelium, which can directly infectlower leaves and stems. In some places thepathogen is more aggressive under hot and humidconditions (eg Queensland).Wet conditions favour disease development of bothspecies and they can both cause disease on brassicacrops (watery soft rot). Both species produce restingbodies (sclerotia) on infected tissue, which cansurvive in soil for up to 5 years (S. minor size up to 3mm, S. sclerotiorum 5 - 15 mm).S. sclerotiorum requires humid conditions to developthe fruiting bodies (apothecia) that produce aerialspores. S. sclerotiorum also infects carrots (soft rot),green and dry beans (white mold) and many otherhorticultural crops.Lettuce drop caused by Sclerotinia.The Bottom line■ Resting Sclerotinia bodies can survivefor 5 years or more.■ Biofumigant green manure crops andcrops more tolerant to Sclerotiniainfection should be used to reduce andprevent build-up of Sclerotinia.■ The fungicide boscalid is a suitablereplacement for procymidone, recentlywithdrawn from use.■ Better application, timing of fungicidesprays and the right volume of water isessential for effective disease control.Winter 2005
VEGEnotesYour levyFungicides are the most common means of controllingSclerotinia diseases. However, there is increasingpressure to produce vegetables with minimum to zeropesticide input and there are few fungicides currentlyregistered for control of S. minor and S. sclerotiorumin Australia.Note: Information on sclerotia numbers can beused as a general guide to predict the level ofdisease pressure in a given field and select themost appropriate strategy for disease control.Action: Keep records of history of Sclerotiniadisease and crops grown in each field. Use therecords to help you select the most appropriatemethod of disease control.The integration of non-chemical controls (e.g.biocontrol agents) and cultural strategies (e.g.biofumigation crops, rotation crops, soil amendments),in addition to fungicide applications, to controlSclerotinia diseases is essential to the sustainabilityof the horticultural industries.FungicidesThe efficacy of registered fungicides is greatlyaffected by disease pressure, weather conditions,method of application, overuse and crop canopy size.Research in Victoria and Tasmania tested a rangeof fungicides for Sclerotinia control and found thatboscalid (Filan ) was an effective replacement forprocymidone.In fields with high incidence of Sclerotinia, twoto three applications of registered fungicides attransplanting and repeated at a two week intervalcan be effective in controlling lettuce drop causedby S. minor. In low disease pressure sites, twoapplications of fungicide can provide excellentdisease control.Fungicides must be directed at the base ofyoung plants and repeated before plantsbecome too large. Irrigation after spraying canhelp to distribute the fungicide into soil andaround the base of plants. For S. sclerotiorum(airborne spores), fungicides should be appliedpreventatively at flowering, ensuring goodcoverage of all flowers.Biological control agentsBiocontrol agents have been proposed as potentialalternatives to fungicides. Biocontrols are fungior bacteria, commercially formulated, which candestroy S. minor sclerotia.These agents use mechanisms such ascompetition for nutrients and space, productionof antimicrobial chemicals (antibiosis) andparasite sclerotia in soil (specialised sclerotialmycoparasite) to reduce their viability.To be effective, biocontrol agents must be appliedstrategically to colonise the soil, or the rootzone, quickly and at high levels. They shouldbe applied so as to directly parasitise sclerotia insoil to reduce viability (incorporate into soil priorto planting) and/or to colonise in the plant’s rootregion (apply into seedling mixes or seedlingplugs prior to field transplanting) to protect frommycelium of sclerotia.HAL project VG00048 focused on improving theformulation, shelf life and application of biocontrolagents (Table 1). Dry powder preparations ofbiocontrol agents can be incorporated into seedlingmixes at sowing. Liquid preparations can also beapplied to mixes and as a drench to the seedlingtransplants.Trials showed commercial seedling mixes witha high percentage of composted pine bark werebetter substrates to incorporate Trichodermaspecies into because they had less naturallyoccurring non-pathogenic microbes, and thereforemore space and food sources for Trichodermabiocontrol agents to grow.Strategic application provides amore reliable pattern and should bedirected at the root zone and underleaves.
Sclerotinia diseasesTabel 1: Biocontrol agents proven to be effective against sclerotia of Sclerotiniaminor and/or suppressing infection in root zone of lettuce plants in overseas trials.Biological control agent (isolate)Mode of action AConiothyrium minitans (Contans) BConiothyrium minitans (A69) CTrichoderma hamatum (6Sr4) CAAs reported by manufacturers.BProphyta, Germany.CLincoln University and Agrimm Technologies Ltd, New Zealand.Specialised mycoparasite of sclerotia of S. minorGood competition for nutrients and mycoparasiteGood competition for nutrients and antibiosisBiocontrol agents can also be incorporated intosoil, but this method is only effective if they aredelivered into the region of soil where the rootsgrow. For example, a maize-perlite method ofinoculum incorporation has delivered good levelsof the biocontrol agents (T. hamatum 6Sr4) to theroot region of lettuce plants.An added effect of biocontrol agents, and someother microbes sold as soil conditioners, is theymay promote better growth of seedlings. Thishas been observed on seedling roots in nurserieswhere there were high levels of biocontrolagent colonisation. For example, high levels ofTrichoderma 6Sr4 and Trich-A-Soil promotedbetter lettuce seedling root growth, and high levelsof B. subtilis GB03 (Companion) promotedbetter lettuce seedling growth.Biological control agents must be registered withthe Australian Pesticides and Veterinary MedicinesAuthority (APVMA) before they can be usedspecifi cally for the control of Sclerotinia diseasesin Australia.Note: Researchers are continually developingand testing new biocontrol products for use inhorticultural crops as soil conditioners, growthpromoters and for improved managementof soil-borne diseases. For updates on newproducts contact your local pesticide supplier,agronomist or State Agricultural Department.BiofumigantsAnother promising non-chemical measurefor Sclerotinia control is the use of inherentproperties of some plants for ‘disinfecting’ soilor suppressing infection. For example, someBrassica crops (e.g. mustard) release volatilecompounds (biofumigants) that are toxic to somesoil pathogens.Green manure Brassica crops that producehigh plant biomass and high concentrations ofbiofumigant compounds offer advantages over lowbiomass manure crops and non-manure rotationcrops for the control of soil-borne diseases.A green manure crop is a crop grown in a croprotation system for incorporation into soil to improvesoil conditions, such as water infiltration and nutrientsand organic matter levels. Information on differenttypes of green manure crops (legumes, brassicas,grasses) suitable for rotations is available fromGovernment agencies and agronomists.Research in Tasmania showed BQ-Mulch (Brassicanapus) and Fumus (Brassica juncea) crops, whenused in rotation with lettuce, reduced Sclerotinialettuce drop incidence by 89% and 46%, respectively.BQ-Mulch produces high levels of biofumigants(isothiocyanates or ITCs) in the roots and appearsto be more effective in suppressing Sclerotinialettuce drop infection than Fumus (mustard), whichproduced high levels of ITCs in its foliage.Other organic soil amendments can produce similarvolatile compounds when incorporated into soil. Forexample, ‘mustard meal’ and ‘neem-cake’ are twocommercially available soil amendments with reportedbiofumigant properties.Cultural and soil amendment strategiesManagement practices such as crop rotations andsoil amendments are becoming important tools formanaging soil-borne diseases, including Sclerotinia.Rotations with crops less susceptible to Sclerotiniacan prevent the buildup of inoculum insoil.Where possible,practice 3-4 yearcrop rotations toprevent the buildup of Sclerotiniainoculum in soil. Theuse of Sclerotinianon-hosts, such assmall grains andcorn, and greenmanure crops can beuseful in reducing thebuild up of inoculumand the incidence ofSclerotinia diseasesin high disease sites.Another example of thedamage caused by Sclerotinia.@ work
VEGEnotesSclerotinia diseasesIncorporating a manure crop.Some soil amendments with high content of nitrogenhave shown potential to reduce inoculum carry overof some soil-borne pathogens.Sclerotinia minor has a wide host range, whichrestricts the choice of a suitable rotation crop. InTasmania, research showed that S. minor infection isclosely correlated with plant architecture.Adoption of these practices may be limited bycropping practices, availability of suitable rotationcrops and soil amendments, and loss of income fromnot growing a commercial crop.Summary and future researchProject VG00048 endeavoured to provide lettuceand other vegetable growers with information onthe development of non-chemical control methods(biocontrol agents, biofumigant green manurecrops), cultural and soil amendment strategies, andimproved application of fungicide sprays for bettermanagement of Sclerotinia diseases in Australia.The project found that control of Sclerotinia diseasescan be improved by:• using green manure Brassica crops in croprotations• selecting rotation crops more tolerant toSclerotinia infection, especially in high Sclerotiniapressure sites• the fungicide boscalid is a suitable replacement forprocymidoneThis project has identified new methods to produce,formulate and deliver biological control agentsinto cropping systems. The results thusfar indicate some biocontrol agents havethe potential to contribute to improved andsustainable disease control, only whenintegrated with other control measures. Thus,biocontrol agents should be considered animportant component of an integrated controlprogram for Sclerotinia diseases.More information is required on thecompatibility of biocontrol agents with farmpractices (e.g. fertilisers, pesticides) and theirsurvival in Australian soils growing vegetablesunder a variety of rotational cropping systems.The use of crop rotations with Sclerotiniatolerant and non-host crops can prevent thebuild of inoculum in soils.Soil amendment strategies such as the use of preplantingapplications of organic and nitrogenoussoil amendment materials have the potential formaking soil conditions suppressive to sclerotia anddisease development. Soil amendment strategiesinvestigated by this project require furtherdevelopment to optimise their use for Sclerotiniacontrol. The effectiveness of other chemical andnon-chemical treatments available for inoculumreduction should also be investigated.Further InformationFor further information you can contact:Oscar Villalta,Primary Industries Research Victoria, DPI,KnoxfieldPhone 03 9210 9222e-mail email@example.comHoong PungServe-Ag ResearchTasmaniaPhone 03 6423 2044e-mail firstname.lastname@example.orgAcknowledgementsOscar Villalta - DPI VicHoong Pung - Serve-Ag Research, TasmaniaBiocontrol Centre - Lincoln University New ZealandDISCLAIMER: Every attempt is made to ensure the accuracy of allstatements and claims made in Vegenotes. However, due to the nature ofthe industry, it is impossible for us to know your precise circumstances.Therefore, we disclaim any responsibility for any action you take as aresult of reading Vegenotes.ISSN: 1449 - 1397Copyright©: Horticulture Australia 2005No part of this publication can be copied or reproduced withoutthe permission of the original authors.VEGEnotes is coordinated, edited & printed by:ARRIS Pty Ltd, ph 08 8303 7247 fax 08 8303 6752Level 1, 50 Carrington StreetSydney NSW 2000 AustraliaTelephone (02) 8295 2300Facsimile (02) 8295 2399www.horticulture.com.auYour levy @ work