Three huge sunflowers grew up to 10′ tall in my yard. We, in Arizona, had a major dust storm and the heads drooped and never have come back up. The large leaves are very unhealthy and also drooping. I watered after the dust storm, having read sunflowers need a lot of water. Nothing seems to help. Now the whole stalk and head is wanting to fall forward. We have them secured to a trestle. What should I do? Cut them down?
Dust on the leaves of a plant can block the sunlight and air flow the same as putting a black plastic bag over them. Try using the hose to spray down the whole plant to try to get embedded dust off the leaves and out of the pores of the plant. It may be too late for this, but it is worth a try.
Beyond this, the relative high speed of the dust particles also causes microscopic cuts to the plant, which can lead to accelerated water loss. Increasing water after a dust storm is recommended to replenish this. Watering daily will not be too much for at least a week after the storm to help keep the water up in the plant.
In the future, if you have enough warning, try to cover your plants with a secured sheet before the storm. You want to treat a dust storm like frost. Keeping the dust off the plant is the best thing you can do to improve the plant's ability to survive a dust storm.