Thanks for the input so far. A few other pieces of info. 1) I increased the amount of water (sometimes sequential days, sometimes longer duration) starting about 3 weeks ago when I first noticed the problem (thinking it was not ENOUGH water that was the problem - I'm sure that's a common response). 2) On the edges of the lawn where there is treated lumber edging I've been dowsing the lawn w/ a hose since that seemed to be more yellow a few weeks ago and/or I thought perhaps my Melnor fan sprinkler wasn't hitting the edges enough. Those edges seem very lush and green. 3) On some spots near the Yucca palm I have where I drove in palm food spikes, the lawn is also noticeably greener (circles 8"-12" right where the spikes went in). So I'll experiment a little w/ the watering volume & frequency (less of each, though maybe in a small patch I'll do more.) Will keep apprised.

The powdery stuff looks like powdery mildew. The plants also show evidence that they're functioning with minimal water (brown edges) and fertilizer (yellow leaves).

If you search for 'grape leaf disease pictures' on google and then look at the 'image' results, you can often identify the disease. I did a quick search and the pictures looked most similar to Phomopsis leaf fungus. I have had this before and it is most noticeable on the young canes. Captan usually does a good job treating this type of fungus.

Hey folks! I posted a few before and after pictures below. It just rained here in Charleston, SC. I have pole beans growing on a teepee and bush beans in a bed 10 feet away. Prior to the rain, the plants displayed some tannish/brown dried patches. The local garden center thought it could be powdery mildew. I treated both bean plants with copper fungicide and neem oil. Treatment separated by 7 days. After the rain, the pole beans look worse!! The patches are now gray and brown and new leaf growth is displaying more concentrated symptoms. The bush beans haven't changed much since the rain. I can't seem to find similar photos on the web. Any help is appreciated! Before Rain- Bush Beans: I removed a few leaves but plants look pretty healthy overall (2nd photo) Before Rain - Pole Beans: A few dry tannish/brown spots but very contained. This is before neem oil treatment. It rained 2 days later. After Rain: Pole Beans. Most plants have symptoms. Last succession planting does not.