Brown spots - Ask Extension
There are brown spots on my herbs. It started on one and has gone to several different plants
Knowledgebase
Brown spots #287097
Asked October 26, 2015, 3:10 PM EDT
There are brown spots on my herbs. It started on one and has gone to several different plants
Marion County Florida
Expert Response
It
is really hard to tell from pictures. Basil
is susceptible to downy mildew – especially in Florida which is caused by Peronospora belbahrii or Pseudoperonospora cubensis and can
spread easily via wind-dispersed spores that it produces abundantly – confirm this
by looking for these spores which look
like dark purplish grey fuzz on underside of leaf when high humidity. (For
basil specific mildew see http://extension.udel.edu/blog/tag/basil-downy-mildew/) You could also have black rot Didymella bryoniae in which case you'd
have Leaf symptoms varying from browning at leaf edges and between veins which
is what your picture looked like to circular tan to brown spots. This is often accompanied by "rot" on
the stem which appear as tan lesions, often with black spots and may have a
dark gummy exudate (see http://www.extension.umn.edu/garden/diagnose/plant/vegetable/cucumber/leavesspots.html). But my best guess at this point is Bacterial
Leaf Spot (Pseudomonas cichorii) (see https://growingsmallfarms.ces.ncsu.edu/growingsmallfarms-basilproblem/). In any case, remove all of the affected
leaves and take them far from your plants.
Do not overwater – all of the plants you specified are mint family and
do not like to be overly wet.