Question
We have a garden in front of our house that we planted earlier this spring. The petunias we planted were coming along beautifully and now all of a sudden are just drying up and dying. Quite similar to what it would look like if you sprayed them with round-up. Very bizarre. None of the other plants are doing this and we have never seen this before. Along with the petunias are marigolds, bottle brush and black eyed susans. And they seem just fine.  We also have some sunflowers planted and they are fine. We have a sprinkler system so they get plenty of water. Any Ideas?

Answer
Louise,
Are they in the front of the bed where they get the brunt of the sprinkler system, and does it go off every day or every other day? If so, they might be either getting too much water or the ground is being kept so constantly wet around them that they have gotten crown rot.  If the roots or the stem at soil level are kept too wet they will rot, and then you see what looks like drying up - the plants first wilt and then turn yellow or brown, because the roots can't deliver water to the top of the plant.  

Other possibilities include that they got the drift from something applied to the lawn, or that a liquid fertilizer was applied that was either too strong or when the plants were dry - fertilizer on a dry plant, or one that's too strong, can cause fertilizer burn.  

The fourth possibility is that the automatic system isn't reaching these for some reason - I've seen flower beds where you think that the entire thing has been watered because the foliage is wet and the ground looks damp on the surface, but the watering is too shallow and brief to throughly soak down into the soil so that the plants are actually drying up.

After the system runs, and each time it runs for the next few days, dig down six inches around the petunias and see what you find.  If you find that it's really dry, that's the problem - if constantly wet, it's rot. (or if the soil smells "swampy")

I hope this helps,
C.L.