basil fungus #363052 - Ask Extension


basil fungus #363052

Asked September 15, 2016, 11:05 PM EDT

After decades of growing many varieties of basil in ground and pots without issue, this yr there is a disease affecting all my plants. Mature leaves fade to yellow (but presumably not chlorosis since no vascular difference), with a grayish brown spot or 2 on each leave. Doubt it could be anthracnose since it is only a spot or 2 on a leaf and some are 1/4" d without any other blemishes on that leaf. Knowing that fungicides are not very effective after the fact , and since an edible, is there any hope? I've heard mancozeb recommended for crops, but would it be appropriate for a leaf crop? I did use a new pack of seeds this yr, so might i assume it is a susceptible strain, so throw out and start with a new brand next yr? tnx

Anne Arundel County Maryland

Expert Response

What you are describing sounds like downy mildew.  Mancozeb and other fungicides would make the basil inedible.  Pick off all affected leaves or cut it off close to the ground.  Regrowth might be free enough from disease to eat.  The fungal spores come in from the south.  There is no reason to throw out your seeds.  There  is no huge likelihood that the seed is the source of the fungus. The next packet that you buy might be infected or it might not.  It never hurts to plant an assortment of cultivars to see if there are any that are less susceptible.   As of yet, we do not have a list of resistant cultivars.  vw
Tnx, but reason i did not think that it is d.m. is that all the google pics show very irregular edges to the affected area but the rest of the leaf remains quite green.  However, 95% of my blemishes have been quite circular, and the whole leaf has faded to light yellow so no green remains.  I know it is difficult without a pic, and will send one if can arrange.  In mean time, here is the closest pic i found on google, but again, my leaves are entirely light yellow and spots (1 or 2 per leaf) more circular.  Regardless, glad for confirmation that no spray will help.
The Question Asker Replied September 16, 2016, 5:51 PM EDT
PS  i should have thought to state that over half the leaves just fade to pale yellow without any blemishes, which leads me to think it is something else.
The Question Asker Replied September 17, 2016, 3:16 PM EDT
The undersides of the leaves hold the identifying characteristic--they are probably purplish greyish, an indication of downy mildew.   If the undersides of the leaves are normal, we cannot identify the disease from the information that  you have sent.  Whatever it is, if you plan to eat it, do not spray and cutting it back may enable you to get edible regrowth.   vw
Yes, that's it.  Even with no blemish on top of leaf, it shows on underside.  Hadn't thought to look there; shame on me.  Tnx for your superlative help.
The Question Asker Replied September 21, 2016, 5:52 PM EDT

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