Thanks all for suggestions. (Great photos, Bev.) What I saw on one semp didn't look like any of the photos supplied by Bev and they didn't look like the online photos of root aphids, fungus gnats and mealy bugs. I only saw the small larvae on one of the affected semps so I'm not sure what that means. I think I'll have to see what happens (and it only happens occasionally) and take pictures to post. But it doesn't sound like this is just rot that occurs every now and then. Pretty sure it isn't just rot because we had no rain for two months and I only watered once each month when the soil was really dry. I'll keep an eye out and report back. Again, thanks for all the comments.
John
