Farm advice wanted: a fungus that keeps returning after treatment on a 5-hectare plot

I farm 5 hectares of cassava in Auckland. This season I'm dealing with a fungus that keeps returning after treatment. I've tried what the local suppliers recommended, but results aren't improving. I'm looking for an agronomist or experienced grower who can look at photos, soil-test results and my planting plan, and advise on what to change. A 30-minute call or exchange of messages would be fantastic. I'm happy to share photos and a soil test. I'm using only what I can afford, so low-cost suggestions are best. I'll share how it goes - and what worked - to help others in the community. If you can't give, please share this page. It does reach people.