How do I prevent and/or cure a fungus on my Iris? Some blooms are normal and some are not

Question

This is the second year for this to happen. The ones that bloom are beautiful but the fungus on a different bloom (on the same stem) never opens. It has now spread to a rhodendrum across the driveway about 25′ away. I pick off the fungal blossoms and incinerate in a bag.

Answer 1

Usually, infections are specific to plant families and won't spread to others. Dropping buds are often weather related, i.e., a cold night while the bud was forming. Also thrip feeding can cause blackened or dying buds.

https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm