What's causing the tan spots on leaves?

Asked September 13, 2016, 9:31 AM EDT

(I apologize if this has been submitted twice, there's no confirmation that it went through.) Photo shows Tan spots on marigold leaves, but the spots are also on a weed growing In the area. Tomato, beans, watermelon growing in area don't seem to be affected with the exact condition. Sunny location Amended soil No mulch Brick wall a few feet behind / fence a few feet to the side. Watered with soaker hoses / possible overhead watering a cpl times

Montgomery County Maryland

1 Response

It is hard to say for sure what is going on here. How does the whole patch look? Is it blooming? Any problems with the flowers?
Marigolds are generally pretty tough, and anything that does bother them tends to be outgrown.
Possibilities that come to mind include rasping damage from plants bugs or tiny thrips (look for insects, but they could be gone now). We see a squiggly line or two which suggests a leaf miner that feeds between the leaf surface. They are not serious either.
Another possibility is a disease of some sort like botrytis, but that would likely eventually show up as a hairy, grey mold on the flowers too.
This late in the season we wouldn't worry too much and do not recommend control.
You might consider pinching some of the plants to increase airflow. Do the soaker hoses spray up droplets? The leaves in your photos look wet, which would encourage disease.

cm