I had just planted sunflower seeds within the last month. The sunflowers love where they are and are already almost a foot tall.
But something has happened within the past week or so. In all of the leaves on pretty much all of the sunflower plants there are brown spots. And not just any brown spots, like a fungus. The brown spots are only on the top part of the leaf, the bottom is green and normal. Open closer inspection I was able to separate the top part of the leave from the bottom part because of this. I notice that inside these brown spots there are little white worms/larvae. What in the world is this? And how can it be fixed? These are only on the leaves of my young sunflowers.
Neem Oil is an Organic solution that acts not only as an insecticide, but also as a repellent and fungicide,,,,I know the fungicide probably isn't needed in your case.
It is relatively inexpensive, and is a good multipurpose product, so it will be less likely to have leftovers go to waste.
Apply early morning/late evening to avoid killing bees.
How'd the flowers do? Start over with more seed... maybe new seed. Season is young yet. :)