Hi Diane,

Powdery mildew is one of the most common diseases we hear about.  It grows easily and is virtually everywhere.  It does not need water and usually starts when it warms up.  It does need humid weather which we have had with the rains and then the hot days.  You see it on the tops of leaves but it can grow on the underneath side as well as stems and flowers.

Thank you for your pictures.  It does look like powdery mildew on each picture.
 
You can remove those leaves affected with the fungus and continue to grow the plants.  Watch for more growth.  Do not compost infected leaves or plant parts.

A simple spray you can make at home is 2 tablespoons of baking soda, with a small amount of veggie oil, regular cooking oil, a teaspoon is sufficient and fill a spray bottle with water.  Shake and spray.  Shake every time you stop spraying to make sure the solution is mixed.  The oil will help the baking soda stick to the leaves.

I would not feed my rabbits food with fungus on the leaves.  However, that is your decision.

Do not fertilize with nitrogen if you keep these plants.  It enhances the growth of the fungus.

Powdery mildew can infect most types of plants.  If you have it on a plant near another valued plant, remove the infected plant and put in the trash.  

The 'why' you have it now?  It has a sufficient growing environment to multiply.  Some things you can do to help prevent it include no overhead watering.  Use a drip system that does not wet the plant.  Good airflow, do not overcrowd the plants.  Sunshine without dampness in the air, which would include no overcrowding as the wind is able to flow through the plants.  This is good not only for vegetables but shrubs and trees.  

If you have further questions, please contact us again.