Answer: Sounds as though you've started your plants and transplanted them correctly, but the weather hasn't cooperated. Sunflowers need all that you've supplied, plus all day sunshine and warm temperatures. If they're overcrowded, or the spring was wet, rust can develop and take over in a hurry. The tell-tale signs of rust are little orange or brown spots, fuzzy looking when they mature enough to release their spores. Rust can kill a plant. If the leaves are wilted and the tops are brown, but you don't see the signs of rust, I'd suspect a vascular problem caused by soggy soil, either from lots of rainfall, or too much water from the hose. I don't think you'll be able to save fully infected or affected plants. Try again next spring, making sure the plants are in fast-draining soil where there's full sunshine and good air circulation.
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