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

Alternaria dauci in carrots

Carrot field infected with Alternaria dauci

Carrot combine

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

Fungicide treated plot Untreated control plot

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

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

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

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

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=34.6-0 11X+0.0001X2-4E-08X3 R2=0.97 Disease severity (%) Infected source field Neighboring affected field Wind direction

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

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

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)

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

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

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)

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 29 77 29 65 119119

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)

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

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

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

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

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

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

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

Contribution of systemic fungicides Disease severity (logit) Time

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

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.