What the heck? I am gone for a week and the population of two-spotted spider mites on my Baptisia australis (baptisia) exploded! I don't know why I am surprised because these guys love it hot and dry and can complete a life cycle in five to seven days under these conditions.
I had one plant infected ten days ago and now all eight of them are loaded with this mite. The lack of rain has also been a positive factor for their development. A good spray with a hose or a heavy shower washes off some of the pests and in this case didn't happen. In the above photo, the plant in the back was the first one damaged and is showing the worst symptoms compared to the others.
It's fairly easy to identify the two-spotted spider mite with a hand lens. The adult is about 1/60" long and ranges from pale yellow in color to orange, green and brown. There are two distinct black spots on what appears to be the back; these dark spots are actually the contents of the gut showing through the body wall according to a Purdue University Factsheet on this mite.
Feeding from the two-spotted spider mite makes the leaves on baptisia kind of look dried out, washed out and tired. Looking at the leaves closely, they are mottled or spotted with tiny yellow pin-sized spots. Given the populations on my plants, leaf drop is inevitable.
If I would have been on the ball earlier, I should have sprayed insecticidal soap or summer horticultural oils. At this point, I will leave them alone and hope for a buildup of beneficial insects to help clean them up a bit. In addition, I will be sure to keep the weed population around the perennial beds down this fall as they tend to overwinter in this habitat.
Purdue Extension Department of Entomology has an excellent handout on Spider Mites on Ornamentals which covers all types of spider mites and recommended controls.