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Weird weather brings botrytis outbreak

Sacramento Digs Gardening
BY Debbie Arrington PUBLISHED MAY 12, 2020

This poor Pink Promise hybrid tea rose was turned into a brown mess by botrytis. (Photo: Debbie Arrington)

Fungal disease loves cool, cloudy, moist conditions

“What is this and how can I fix it?”

That question came attached to a photo of what should have been a big beautiful red rose. Instead, each petal was deeply edged in brown.

In the days ahead, more Sacramento roses will seem to stop opening in mid-bloom and suddenly become covered with spots and brown patches. If left on the bush, these flowers turn to yucky gray mush.

It’s an early outbreak of botrytis, a common fungus that attacks a broad range of ornamental and edible plants.

Usually, local gardeners don’t see Botrytis cinerea on their roses until October or November. But recent weather conditions have been just right for this opportunistic pathogen. Botrytis loves temperatures in the 70s, cloudy afternoons and a little rain.

It’s that splash of moisture that really launched this attack – both in April and now in May. Botrytis needs moisture for growth in plant tissues and what it loves are tender flower petals. It can’t seem to resist a wet bud on a cool, cloudy day.

Nicknamed gray mold, botrytis will eventually overwhelm the flower and turn it into soft mush. The earliest stages look like pink measles or brownish water spots on light colored flowers. Those brown spots quickly grow until they consume the whole petal. The fungus grows so fast, the flower never fully opens.

Although botrytis is common in the fall, a spring attack seems worse because we have more flowers in the garden.

Besides roses, botrytis also attacks African violet, asters, begonia, carnation, chrysanthemum, cyclamen, cymbidium, gerbera, geranium, gladiolus, hydrangea, marigolds, orchids, petunia, poinsettia, primrose, ranunculus, snapdragon, zinnia and many other garden favorites.

According to UC Integrated Pest Management program, the best control of botrytis is “good sanitation.” Clip off infected blooms, put them in a plastic bag and dispose 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.

When the heat returns (which will be soon), botrytis will disappear – it can’t stand temperatures over 90 degrees. But expect it to come back again in October – especially after the first fall rain.

For more information on botrytis, check out these pest notes from UC IPM: http://ipm.ucanr.edu/PMG/r280100511.html

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Keywords:

gardening Sacramento integrated pest management roses botrytis pathogens disease control UC IPM plant diseases

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Garden Checklist for week of Oct. 13

Our break in the heat has arrived. Time to get planting!

* October is the best month to plant perennials in our area. Add a little well-aged compost and bone meal to the planting hole, but hold off on other fertilizers until spring. Keep the transplants well-watered (but not wet) for the first month as they become settled.

* Now is the time to plant seeds for many flowers directly into the garden, including cornflower, nasturtium, nigella, poppy, portulaca, sweet pea and stock.

* Plant seeds for radishes, bok choy, mustard, spinach and peas. Plant garlic and onions.

* Set out cool-weather bedding plants, including calendula, pansy, snapdragon, primrose and viola.

* Reseed and feed the lawn. Work on bare spots.

* Dig up corms and tubers of gladioli, dahlias and tuberous begonias after the foliage dies. Clean and store in a cool, dry place.

* Treat azaleas, gardenias and camellias with chelated iron if leaves are yellowing between the veins.

* Clean up the summer vegetable garden and compost disease-free foliage.

* Harvest pumpkins and winter squash.

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