1.9 Case study: Integrated management of Alternaria blight in carrots

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1 1.9 Case study: Integrated management of Alternaria blight in carrots
Introduction Efficacy of sole control measures Integrated of control measures Concluding remarks

2 Alternaria dauci in carrots

3 Carrot field infected with Alternaria dauci

4 Carrot combine

5 Chemical management of A. dauci
1 2 3 4 5 6 7 8 9 Time (days) Sprinkler irrigation Air spraying Ground spraying

6 Fungicide treated plot Untreated control plot

7 For management of A. dauci
up to 4 sprays are applied each week and up to 40 sprays are applied in a growing season !!!

8 Objective of the research
To develop an integrated management strategy that will: 1. Reduce the number of sprays applied in a growing season; 2. Prevent disease development and yield losses

9 Management of A. dauci Sole application of measures
Chemical fungicides (protectant, systemic) Cultural measures (spatial organization of planting, sanitation, irrigation type) Genetic (cultivar resistance) Integration of measures Chemical and drip irrigation Cultivar resistance and chemical control

10 Temporal and spatial dissemination of spores
4 8 12 16 20 24 100 200 300 400 Hour of the day No. of spores trapped (m3 air/h) west east

11 Spatial influence of an infected field on neighboring fields
Distance from source field (m) 100 200 300 400 500 600 700 10 20 30 40 Y= X X2-4E-08X3 R2=0.97 Disease severity (%) Infected source field Neighboring affected field Wind direction

12 Spatial organization of plantings
Wind direction 1 2 3 4 4 7 6 5

13 No. of spores trapped (m3 air/h)
Effect of sanitation: burring of infected debris after harvest in the soil Hour of the day No. of spores trapped (m3 air/h) 4 8 12 16 20 24 100 200 300 400 500 Before after

14 Optimization of chemical control
Efficacy of various fungicides 20 40 60 80 100 Untreated Disease severity (%) Bravo, Score 60 70 80 90 100 110 Time (days after planting)

15 Why the systemic mobility of the fungicide is not an advantage?
Development of A. dauci on carrot leaves

16 Why the systemic mobility of the fungicide is not an advantage?
Protectant fungicide Systemic fungicide

17 Optimization of chemical control
Optimal timing for spraying initiation 100 80 Tebuconazole 60 Control efficacy (%) 40 mancozeb 20 Disease onset -20 -10 10 20 Time from disease onset and spraying initiation (days)

18 Optimization of chemical control
100 Untreated Last 4 80 60 Disease severity (%) Disease onset Optimal timing for spraying initiation First 4 40 20 8 sprays 80 90 100 110 120 Time from planting (days) Date of praying (DAP): Treatment Initiation Termination First 4 sprays Last 4 sprays 8 sprays

19 Optimization of chemical control
Optimal timing for spraying termination Last spray (days before harvest) 100 80 -14 Control -42 -29 -21 Disease severity (%) 60 40 20 20 10 Time before harvest (days)

20 Time from planting (days) Time from planting (days)
Disease severity (%) Time from planting (days) 60 70 80 90 100 110 20 40 cultivars Genotype resistance 20 40 60 80 100 70 90 110 Disease severity (%) Time from planting (days) Genotype resistance + fungicides

21 Time from planting (days)
Disease severity (%) Time from planting (days) 20 40 60 80 100 Overhead Drip 50 70 Type of the irrigation system 3/9 9/9 15/9 21/9 27/9 6 8 10 12 Hour of foliage dryness Overhead irrigation

22 Integration of drip irrigation and application of fungicides
Disease severity (%) Time from planting (days) 20 40 60 80 100 Overhead Drip 50 70 + fungicide

23 Effects of drip irrigation on the epidemic and on fungicide efficacy
Shorter wetness duration 70% host environment pathogen

24 Effects of drip irrigation on the epidemic and on fungicide efficacy
Lower weathering of fungicide from the foliage 30% host environment pathogen

25 Contribution of sanitation and spatial organization of planting
Disease severity (logit) Time

26 Disease severity (logit)
Contribution of cultivar resistance, drip irrigation protectant fungicides Disease severity (logit) Time

27 Contribution of systemic fungicides Disease severity (logit)
Time

28 Integration of control measures Disease severity (logit)
Resistant cv. +Drip irrig. Disease severity (logit) +systemic fung. +spatial organization Time

29 Concluding remarks The major means for suppression of Alternaria blight in carrots is chemical application of fungicides. Up to 40 sprays are currently applied in a growing season. Use of resistant cultivars, drip irrigation, burying infected debris after harvest and re-organization of planting in space, each may contribute to disease suppression. Integration of several control measures enable to reduce the number of sprays, without increasing the risk for disease outbreaks.