Plant Diseases/Butterfly Bush Problem
QUESTION: Hello, Dr. Vann. Thanks again for answering my question. I have two Black Knight Butterfly Bushes. They are planted on the south-west corner of my house where they receive morning shade and afternoon sun. I noticed about a month ago that they were beginning to get brown colored spots on the leaves. Now about half of the leaves are dead on each of the plants. There is, however, new growth at the base of each plant that doesnít seem to be affected yet.
I have included links to a couple of photos at the end of this question. From the photos, can you tell if they have a fungus or do you think it is just a climatically caused situation as a result form the unusually wet cool summer followed by a hot, dry late August and early September? I hope the photos are clear enough. If you canít tell from the photos, please let me know, and I will get you some better ones.
Tim Elliott (SC Kansas, zone 6b)
(1) Can you send a closeup of a group of representative symptomatic leaves? Try to get as close as you comfortably can. Review your images on your computer before sending. They will need to be in focus and crisp.
(2) Do the leaves become yellow first, then get spots or vice versa?
(3) Do the older leaves show symptoms before/after/or at the same time as the younger leaves?
---------- FOLLOW-UP ----------
QUESTION: Dr. Vann,
Below are several links to close-up photos of the leaves. As far as I can tell from my observation and from what I remember, the leaves get the brown spots before turning yellow, which can also be seen on the younger foliage in a couple of the photos. It appears that the older leaves get the spots before the younger leaves, which can also be observed in the photos...I think. Some of the younger leaves have no spots at all while a few are starting to get them. Also, the photos you see of the yellowing leaves with the spots is how all of the older leaves are now. I cannot find a single large green leaf on either plant. But the leaves are not wilted and the plant is not drooping. Also, the soil around each plant is moist without being boggy.
Tim (links below)
Older Leaves with Younger Leaves:
Thnx for your images!
I do not recognize an infectious disease here. This damage looks like a good candidate for spider mites. These tiny (pin point sized) 8-legged critters can definitely be an issue, especially during hot weather. Enough of them can burn up leaves. They start out by feeding on the under surface of the leaf. That is the best place to look for them. If they get bad enough, you can often see small delicate webbing in the area where the leaf petiole attaches to the stem. These things are hard to see w/o magnification. Usually a 10X lens is adequate however. You can also tap groups of 2 or three affected leaves over a white sheet of paper. They can better be seen on this white background when they crawl. They appear reddish-orange. Try this on several groups of leaves OR get yourself a magnifying glass and look on the undersurfaces of several leaves. Often the white sheet test is easier!
FYI. Marigolds are considered spider mite magnets!!Ha-Ha
Eventhough these things are not true insects, there are several effective insecticides such as insecticidal soap that can help. This and other insecticides will not reverse the damage on afffected leaves, but can protect newer leaves that are forming.