Cereal Disease Control 2024 Part 3 Disease Control Stategies in Wheat

1-* Sexual (ascospores) and Asexual (pycnidiospores) reproduction during the season 2-* when airborne ascospores are active in the growing crop then rainfall is not critical for infection spread 3-* hence there may be continuous development of the sexual phase of this disease - the disease evolves over time 4-* the pathogen may respond over time to selection exerted either by the introduction of new cultivars or by the application of site-specific fungicides (Hunter et al 1999) 5-* this disease is dynamic and changing over time slide 6= lifecycle Slide 8 The disease triangle

• Pathogen -Environment -Host

*Host Varietal resistance poor CROP Inoculum Early sowing, mild autumn, long spray intervals DISEASE Environment Rainfall, leaf wetness, multiple septoria episodes WEATHER

• 2002 was the highest disease pressure year in at least a decade • disease control on wheat started very well and finished very variably • high spend on strobilurin-based fungicide programmes with over 90% of crops getting strob at T2 • uneven control of Septoria across fields e.g. disease buildup in a very unusual spatial pattern • unexplained differences in efficacy of disease control between fields, farms, localities, regions • Lab tests found a new disease strain with a G143A mutation ( see next slide)- look at slide 14,15,16,17,18,19,20

• protective, eradicative and curative activity • reliable systemic movement • site-specific mode of action - DMI inhibitors • good broad-spectrum activity • good persistance of disease control ( 20-30 days ) • useful curativity on a number of key diseases like Septoria , Rhynco / Net blotch / Rusts

1- – analysis of experiments show that in last 2 decades the field performance of triazole fungicides against Septoria has been significantly poorer 2– due to the changing sensitivity to triazoles in the Septoria population 3– Moderate Septoria control can still be achieved with triazole fungicides but dose is more critical

1-* Recommend Practices – Limit the number of applications – To use the full-recommended rates – To mix fungicides with different modes of action 2-* Farm Practice – Limit the number of applications – to reduce cost – To use appropriate rates – to optimise returns – To mix fungicides with different modes of action – to optimise control and to increase spectrum of control 3- Dose rate

1-* multi-site inhibitors hence chances of resistance developing are very slight 2-* Preventative products with no curative activity 3- * Applied at 1.0-1.5 l/ha ( 500-750 grams of a.i.) * If applied in a situation where curativity is required its effect will be reduced * To be effective as a partner in an anti-resistance strategy contact products need to be applied preventatively 4-* There is some evidence of reduced triazole curativity when chlorothalonil mixtures are used in a curative situation (9-12 days curative 5-* There are label restrictions and CTL did not have its licence renewed in 2020 so its no longer on the market

1- Single site Mode of Action - SDHI 2- Good efficacy but in partnership with existing chemistry at T1 and T2 - partner product is also critical - uncertainty about optimum timing if only applying once a season 3-What is the risk of resistance – medium-high Mutations are found and well documented 79 and 152 mutations 4-Well integrated programmes are v important 5-Mixing options with other chemistry are essential

– early-season : GS 30-37 - CTL / triazole / SDHI – T Zero and T1 – sprays at GS 30 and GS 32 expected – mid-season : GS 37-50 - triazole / CTL / SDHI ( + triazole) * split T2 application in difficult growing season – late-season : GS 55-end – triazole (strob) ( + triazole) – T3 ( ear spray)

• CTL off the market in 2021 / replacement is Folpet ( cost-effect ??) – SDHI resistance moved quickly to moderate resistance – Current triazoles have moderate to high resistance

– Revysol (BASF) – 2020 ‘designer’ triazole fungicide to which current mutations are ‘sensitive’ – recently in 2023/2024 problem mutations emerging – Inatreq – 2021 : new mode of action fungicide from Corteva

– ISY from Bayer – another SDHI option – Pavecto 2027~ (Sumitomo/BASF) – novel QoI fungicide – Adepidyn (Syngenta) – 2026 ? : 3rd Generation SDH