Is this powdery mildew??

Bob - Thanks for the images. The spotting actually doesn't really look like powdery mildew. It does look like damage from high light. What are your light levels like in the greenhouse?

Bob,
Not sure on how high light would account for your pictures under the leaf. Have you been applying weekly calcium sprays? Noticed on one of your pictures that the bract was damaged and there was a spot right there. How is the greenhouse for drips. Is it through out the crop or only in a section? If it's really bad, with were you are located there is a wealth of knowledge at Ball. Call Chuck Otto or Jim Nau. I'm sure they can help or direct you to the right person.
Jim Clesen

I'm glad it doesn't look like Powdery Mildew. It is very localized in the greenhouse. My first thought was water dripping on the bracts. The first place the spots showed up was under a recently fixed glass pane. The spots were on several different plants in that area and not entirely under the glass pane.

I then noticed another spot developing on the end of a bench near the aisle of the greenhouse. These plants were probably under the most water stress. I discovered another area recently in the middle of a bench.

All in all I have about 40-50 plants with spotted bracts. Most only have one or two spots on the bracts. I'm currently just practicing removal of the damaged bracts.

About light levels, we have had 7 days at or above 50 Klux since November 15th. One day was as high as 60 Klux. We had 3 days near 30 Klux. And we had 6 days at or below 10 Klux. That is back to November 15th. I first noticed the spots on November 25th.

Hi Bob - It is hard to say for sure what this type of spotting is from. It doesn't look like bract edge burn, usually on a red bract the edges will become necrotic and may take on a bluish cast if botrytis sets in.

High light levels at any time during production can cause damage similar to this, especially if the plants are under moisture stress but is doesn't look like your levels have been excessive at this stage in production.

Moisture condensing or dripping from the roof is also a possibility.

The most important thing to keep in mind is that any damage can be a perfect place for botrytis to set in. Removing the damaged tissue is a good idea as well as a fungicide application for botrytis. Decree would be a good choice on open bracts. It offers good prevention and when applied correctly will not leave residue or spotting. And as always when we are talking about botrytis prevention, don't forget your environmental controls (reducing relative humidity, minimizing leaf wetness, good airflow, etc.).

How is the situation right now? Do you feel like the spotting is spreading?

I have done some bract removal to get rid of what I was seeing and have not been seeing any new development. I still have a couple plants with the damaged bracts. I've been keeping a close eye on them and there seems to be no further development.

Water drops could have been the culprit. I had them growing under warm days making the bracts expand a little faster. If could water hit them from the roof, it could have had more of an effect on this tender growth.

The only varieties it has been evident on were Prestige and Cranberry Punch.