Management and control of apple powdery Mildew Angela Berrie and Robert Saville East Malling Research

Subjects covered Apple powdery mildew  Background  Life cycle  The disease  Control  Fungicides  Research

Apple powdery mildew – The disease 1  Second most important disease of apple in UK  Present in all orchards, apple cultivars vary in susceptibility  Cox and Braeburn very susceptible. Golden Delicious more tolerant  Previous research at EMR in 1980s (Denis Butt) showed that for cv. Cox an average of 8% mildewed leaves over a season will result in reductions in yield and fruit quality

Apple powdery mildew – The disease 2  Mildew is a debilitating disease affecting most tree parts and reducing yield and fruit quality  Reduces yield directly by reducing number of viable blossoms and indirectly by reducing tree vigour  High incidence of mildew results in russeted fruit  Many commercial apple orchards high levels primary and secondary mildew  Requires season-long spray programmes to achieve control sprays

Apple powdery mildew - Lifecycle Primary mildew Secondary mildew

Apple powdery mildew – Epidemiology  Young leaves are most susceptible  Mildew spores do not need surface moisture to germinate on leaves  So, provided there is young leaf tissue (growing shoots) and it is not raining every day in summer is an infection day for mildew  In favourable weather (warm - > 18 o C, cloudy, humid) the fungus can infect leaves and produce sporing mildew colonies in about 4-5 days  So mildew can build up rapidly in summer on extension growth

Apple powdery mildew – Management and control  Mildew inoculum level is key factor in determining the seasonal epidemic  Control strategies rely on keeping primary mildew levels low  Season-long sprays required to achieve this (Green cluster (April)-end of shoot growth (July) and post-harvest if regrowth occurs)  Strategy for control based on –  monitoring mildew incidence 7-14 days  Adjust fungicide product, fungicide dose, spray interval and volume to match mildew epidemic activity  Proven strategy but very few growers follow it  Currently limited range of fungicide products which probably contributes to poor control – reliance on DMI / triazoles – Systhane and Topas  Limit to number of applications

Apple powdery mildew – Management and control  Management system developed by Denis Butt at EMR in 1980s  Assess primary mildew at start of season  Primary blossom  Primary vegetative Low = < 0.5% Moderate % High = > 2.0%  Gives measure of control success in previous year  High primary blossom = mildew problem in June / July  High primary vegetative = mildew problem at end of extension growth  Also gives measure of inoculum for current season

Apple powdery mildew – Management and control  Monitoring secondary mildew incidence on extension growth 7-14 days – Record number mildewed leaves in top 5 youngest on shoots per orchard Low = <10% Moderate = 10-30% High = > 30%  Adjust fungicide product, fungicide dose, spray interval and volume to match mildew epidemic activity  Continue sprays as long as extension growth continue  Sprays may be needed post-harvest  Alternate products to minimise resistance risk

Fungicides for apple powdery mildew in UK Active ingredient Fungicide product eg Mode of action Max No of treatments Chemical group bupirimateNimrod E/P 4Hydroxy- pirimidine cyflufenamidCosine E/P 2amidoximes fenbuconazoleIndar E/P 10DMI (triazole) kresoxim- methyl Stroby P 4Strobilurin (Qol) meptyldinocapKindred P 2Phenyl-acetamide myclobutanilSysthane E/P 10DMI (triazole) penconazoleTopas E/P 10DMI (triazole) Potassium bicarb various E Max dose 60kg/annum inorganic pyraclostrobin + boscalid Bellis P 4Strobilurin (Qol) + SDHI pyraclostrobin + dithianon Maccani P 4Strobilurin (Qol) + quinone Sulphurvarious E/P See labelinorganic

SCEPTRE project - Aims  Gap-filling – identifying fungicides or BCAs for control of diseases where products absent or limited  Identifying effective and crop safe actives  Develop sustainable IPM systems

SCEPTRE - Consortium members

SCEPTRE Project – Control of apple powdery mildew  Many orchards mildew is difficult to control  Several possible reasons but a main contributory factor is limited range of fungicides available  Heavy reliance on triazole fungicides – myclobutanil and penconazole  Main objective to identify new fungicides and biofungicides  Separate trials on fungicides and biofungicides

SCEPTRE Project – Control of apple powdery mildew Fungicide evaluation  2011 and 2012 experimental fungicides evaluated as 5 spray programmes  Most effective products from these trials combined in programmes in 2013  In 2014 best products combined into whole season programmes and evaluated in large orchard plots  Selection of products for programmes based on  Fungicide group (eg DMI, SDHI, QoI, novel)  Other diseases controlled

SCEPTRE Project – Control of apple powdery mildew Fungicide evaluation Method  Small plot experiment on cv. Cox 3 tree plots 4 reps  Treatments applied using Stihl air-assisted sprayer at 500 L/ha  Routine fungicide programme for scab and mildew control from bud burst to start of trial  5 spray rounds applied at approx day intervals from mid June  Trial targeted at control of secondary mildew  Mildew assessed on top 5 leaves on 7 occasions

SCEPTRE Project – Control of apple powdery mildew Fungicide evaluation Treatments 2012 Treatment number Sceptre code Active ingredient Rate of product / ha Chemical group 1Untreated--- 2Systhanemyclobutanil330 mlDMI 3APL LSDHI + DMI 4APL kgQoI + 5APL LSDHI + DMI 6APL-25a1.0 L SDHI + DMI 7APL L Aryl-phenyl- ketone 8APL L L SDHI + 9Cosinecyflufenamid0.5 L Phenyl acetamide 10APL-158 Potassium bicarbonate + Sulphur 10 g/L + 5 L Inorganic

SCEPTRE Project – Control of apple powdery mildew Fungicide evaluation Results 2012 % Mildewed leaves

SCEPTRE Project – Control of apple powdery mildew Fungicide programme evaluation 2013 Treatment Product / Timing 1 13 June 2 20 June 3 3 July 4 17 July 5 26 July Untreated----- StandardSysthane P1APL-32 CosineAPL-87APL-32 P2APL-17 CosineAPL-87APL-17 P3APL-25a CosineAPL-87APL-25a P4APL-128 CosineAPL-87APL-128 P5APL-32 APL-159 APL-32 P6APL-32 Kumulus DF APL-32 Experimental 1APL-88 Experimental 2APL-118

SCEPTRE Project – Control of apple powdery mildew Fungicide programme evaluation Results 2013

UntreatedSysthane Programme 5

SCEPTRE Project – Control of apple powdery mildew Programme evaluation Conclusions  Mildew in untreated plots increased rapidly to almost 100%  All treatments reduced the incidence of mildewed leaves  Least effective was the standard treatment Systhane  Most effective treatments were P1, P5, Experimental 1 and Experimental 2  In 2014 full seasons’ programmes (10-15 rounds) of products will be evaluated

SCEPTRE Project – Control of apple powdery mildew Programme evaluation 2014  Large plot trial 6 rows of apples 3 rows Cox and 3 rows Gala  2 replicates  Season long programme of 13 spray rounds at 7-14 day intervals  3 programmes compared –  P1 – Based on existing approved products  P2 – Experimental programme A  P3 – Experimental programme B  Sprays applied at L/ha  Mildew recorded on top 5 leaves on 8 occasions to assess success of programmes

SCEPTRE Project – Control of apple powdery mildew Programme evaluation 2014 TimingStandard programmeExperimental programme 1Experimental programme 2 Bud burst 12 March Dithianon WG 24 MarchDithianon WG + Indar Pre- Blossom 10 April Captan + Kindred Blossom 28 April Systhane + CaptanAPL-128APL MaySysthane + CaptanAPL-32APL MaySysthane + CaptanAPL JuneCosine 9 JuneTopas + CaptanAPL-88 + Captan 17 June Systhane + Stroby + Captan APL-25a + Captan 23 June*Cosine + Captan 30 JuneTopas + CaptanAPL-25a + Captan 9 JulyKumulus + CaptanAPL-88 + Captan 14 JulyTopas + CaptanAPL JulyTopas + CaptanAPL-32APL-17 7 August*Topas + Captan

SCEPTRE Project – Control of apple powdery mildew Programme evaluation – Results 2014 Standard programme Experimental programme 1 Experimental programme 2 cv. Cox cv. Gala

SCEPTRE Project – Control of apple powdery mildew Programme evaluation Conclusions  High incidence of primary mildew in the orchard  All three programmes reduced disease epidemic through the season  Experimental programmes resulted in lower incidence mildew at end of season

SCEPTRE Project – Control of apple powdery mildew Evaluation of biofungicides 2012  Pot experiment using MM106 rootstocks 7 pots per plot, 6 replicates per treatment  Mildew-infected potted trees present in each block as mildew inoculum source  Treatments applied using knapsack sprayer at 1000 L/ha  5 spray rounds applied at approx. 7 day intervals  Spray dates 13 June, 20 June, 26 June, 4 July, 12 July  Mildew assessed on 3 occasions on top 5 leaves

SCEPTRE Project – Control of apple powdery mildew Evaluation of biofungicides 2012 Products Treatment number Sceptre codeActive ingredient Rate of product / ha Product type 1Untreated -- 2Systhanemyclobutanil330 mlfungicide 3APL L/haPlant extract 4APL-146 Potassium bicarbonate 10 g/LInorganic salt 5 APL-160Sulphur5 L/ha Inorganic fungicide 6 APL-158 Potassium bicarbonate + Sulphur 10 g/L + 5 L/ha Salt + fungicide 7APL-0610 Lbacteria 8APL-3810 Lbacteria 9APL gMyco parasite 10APL-9010 ml / LPlant extract 11APL ml/L A + 1 ml/L B ml/L Addit Alternative chemical

SCEPTRE Project – Control of apple powdery mildew Evaluation of biofungicides 2012

SCEPTRE Project – Control of apple powdery mildew Evaluation of biofungicides 2012 Results % mildewed leaves mean of 3 assessments

SCEPTRE Project Evaluation of biofungicides Conclusions  Mildew incidence in untreated trees >70% mildewed leaves  All of the test products reduced mildew incidence  Best control achieved with Systhane and APL-160  APL-160 performed better on own than in combination with APL-146 (SF2012-APL-)

SCEPTRE Project Evaluation of biofungicides / fungicide programmes 2014  Evaluation of programmes combining fungicides and biofungicides  Small plot orchard trial (3 tree plots) on apple cv. Cox 4 replicates  Sprays applied at 500 L/ha. 10 spray rounds at ~7 day intervals  Systhane as fungicide standard  8 Fungicide / biofungicide programmes evaluated  2 managed programmes where product choice determined by disease incidence  Mildew assessed on top 5 leaves on 8 occasions

SCEPTRE Evaluation of biofungicide / fungicide programmes 2014 Treatment Number Product / Timing 1 22 May 2 2 June 3 9 June 4 16 June 5 23 June 6 30 June 7 7 July 8 14 July 9 21 July July Systhane 3APL-32 APL-105 APL-32 4 APL- 157* APL-32 5 APL-90 APL-32 6 APL-06 APL-32 7APL-17 APL-105 APL-17 8 APL- 157* APL-17 9 APL-90 APL-17 10APL-17 APL-06 APL managed APL-17 APL-88 APL-06CosineAPL-157APL-06APL-146APL managed APL-32 APL-88APL-06APL-157CosineAPL-06APL-157APL-146APL-32 FungicideBiofungicide

SCEPTRE Evaluation of biofungicide / fungicide programmes Results

SCEPTRE Project - Evaluation of biofungicides / fungicide programmes Conclusions  High incidence of primary mildew in the orchard at the start of the trial  Untreated plots mildew rapidly increased to 100 % mildewed leaves  All programmes reduced disease relative to untreated  An initial decrease in disease observed at the start of ALL the programmes (coinciding with chemical fungicides)  Mildew epidemic increased once biofungicides were included in the programme.  Managed programmes were as good/better than Systhane standard.

SCEPTRE – Control of apple powdery mildew Overall conclusions  Promising new fungicide products for mildew control were identified  When these products are registered they will most likely be limited to a maximum of 2-4 sprays per season  This presents problems for a disease which requires sprays per season for control  Biofungicides were only partially effective and in general are also expensive making their use as part of a programme with fungicides impractical

Control of apple powdery mildew Future research  Future work will focus on evaluating plant strengtheners / elicitors  These may be cheaper and if effective could form the basis of a programme with reduced fungicide use  They may also be effective against other apple diseases and possibly have benefits for fruit yield and quality

Thanks to HDC and Defra for funding and to Trials team at EMR for applying the sprays Karen Lower, Tom Passey, Joyce Robinson for assistance with the trials Acknowledgements