Could these spots be anything but Botrytis?

Cercospora or alternaria?

We can't really tell from the images but are you seeing in tan or yellow halos around the spotting? Any sporulation?

Corynespora bract and leaf spot can cause black to brown spotting on the bracts but generally they are much larger. It can look very similar to botrytis but corynespora produces brown conidia where botrytis produces gray conidia. The spots of corynespora are also generally surrounded by a halo.

With Alternaria the spotting begins as small spots with tan centers.

It is not uncommon as the temps drop to see spotting on the bracts like this and it is usually botrytis. At night moisture condenses on the foliage and bracts and it’s wet long enough for botrytis spores to germinate. When the sun comes up the moisture dries and so does the infection leaving small spots. Unless you can see the characteristic gray spores of botrytis, the only way to know for sure which pathogen you have would be to have the material tested.


Corynespora, Alternaria, and botrytis are all more prevalent when the relative humidity is high and airflow is reduced in the greenhouse. Minimizing leaf and bract wetness and reducing relative humidity are both very important. Fungicide applications are also important, especially if your environment is conducive to these types of pathogens that require high relative humidity to germinate.

No sporulation or halos

The bottom side of the leaf these spots show a tan center.

What do you think?


Thanks again!

You can see a tan center with botrytis - when the infection dries up it can look tan and papery. Take an infected leaf and place it in a plastic bag. If it is botrytis in the humid environment of the bag you will see gray fuzzy mold which is the mycelia and spores from the botrytis. If you don't see any spores or mycelia after about 24 hours in the bag or what you do see is not gray let us know and you should have the material tested for other pathogens.