Foggy weather brings on attack of gray mold

So much for Christmas roses; three weeks of foggy weather finished them off.

After basking in the warmth of a sunny November, Sacramento area gardens have suffered under chilling, damp fog. Moist air (and so little sun) brought on a host of fungal diseases, finishing off summer annuals and vegetables.

In the rose garden, this persistent foggy weather ushered in a widespread outbreak of gray mold. That’s the common name for botrytis, a fungal disease the turns promising buds into ugly mush.

Gray mold – which actually looks more tan or brown on the rosebud – needs moisture for growth in plant tissues, particularly tender flower petals. To prevent outbreaks, rose gardeners strive to keep flower buds dry. That’s all but impossible on damp, foggy days.

And in Sacramento, we are already in record “Gloomy Day” territory. Through Sunday (Dec. 14), Sacramento Executive Airport had recorded 22 consecutive days of fog and low clouds, eclipsing the previous “Gloomy Days record of 16 set in January 2005.

This non-budging inversion layer also kept us very chill – Sacramento hasn’t seen 50 degrees since Dec. 4. Those low temperatures push plants (including roses) into dormancy.

Thanks to warm fall weather, I had dozens of rose buds in my garden and was hoping to make some Christmas bouquets. But after so much chilly fog, I’ll have few if any roses for my holiday table.

Gray mold starts out looking like pink measles or brownish water spots on light-colored flowers. Those brown spots rapidly grow until the fungus consumes the whole petal. The flower never fully opens.

Another victim to gray mold this season: Poinsettias. If left outside, they turn to mush.

Gray mold also attacks African violet, asters, begonia, carnation, chrysanthemum, cyclamen, cymbidium, gerbera, geranium, gladiolus, hydrangea, marigolds, orchids, petunia, primrose, ranunculus, snapdragon, zinnias and many other garden favorites.

According to UC Integrated Pest Management program, the best control of gray mold is “good sanitation.” Clip off infected blooms, put them in a plastic bag and dispose of them in the trash. Do not compost them; that just recycles the spores back into the garden. Pick up fallen blooms and petals around the bush and dispose of them, too.

(Since this is already pruning time, I’ll remove those infected blooms in a pass through my garden before I tackle pruning the canes.)

After pruning, rake out old mulch and fallen foliage. (This contains other fungal spores, too, for powdery mildew, rust, black spot and other rose diseases.) Then, dispose of that old mulch and replace it with fresh mulch.