Sunflower problems

i hav 1 to & mine dose the same not much help am i.

The water could be draining out too quickly, There may be a grub in the soil eating away at the roots and lower stem or it could be the wind is blowing so much that the water is drying out from the soil and through the leaves at the mo. The wind is warm and will dry the stem and leaves too quickly. Hope this is of help otherwise go to local garden centre and ask if it is local conditions.