Question

marigold disease   Hi Jennifer, I am living in north India with tep ranging between 22-30 deg. I have a few potted marigold which are showing some signs of disease.I use organic compost in equal ratio with garden soil.I am attaching a photograph for you.I greatly appreciate this forum and the initiative taken by you.
Warm Regards
Dr Shailesh Mehta

Answer
Hi Dr Mehta,

I am sorry to tell you, but I'm relatively certain that your marigold is affected by a plant virus.  The most likely culprit is Tomato spotted wilt virus (TSWV) or Impatiens necrotic spot virus (INSV).  I have seen TSWV on marigold a few times and the symptoms were identical to your photo.

Unfortunately, there is no cure for a plant virus.  The recommendation is to discard and replace the plant.  It is likely that the plants were infected in the greenhouse by an insect called thrips.  It is also possible that the insects were present in nearby plants and moved to your marigolds.  These insects can carry the virus and transmit it to healthy plants.  

For more information about these viruses and thrips, you can review the factsheet at this website:
http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_SpottedWilt.htm

If you want to have your plant tested, you may want to contact your local county extension office.  I am not certain if the diagnostic lab at Purdue charges a fee for testing, but the county agent can let you know.  The contact info for your local office can be found at:
http://www.ag.purdue.edu/extension/Pages/Counties.aspx

Good luck with your plants!
--Jen