My sunflowers have developed what I think is a disease in the top leaves surrounding the growth point. These leaves are dark brown and curling up on themselves. I have pulled a few leaves off and checked them for insect pests but there are no signs ofthat. I have found various diseases online but none match these symptoms. The seeds have been germinated in my greenhouse in trays of compost, so there should be no soil borne disease. I did have this problem last year though and some plants died, others had poor flowers.
Certified GKH Gardening Expert
If you found no signs of pests, it could be due to a fungus of some sort (of which there are many). Treat them with fungicide, like neem oil, and see if this helps any.