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Weird weather brings botrytis outbreak

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:


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Dig In: Garden Checklist

For week of March 26:

Sacramento can expect another inch of rain from this latest storm. Leave the sprinklers off at least another week. Temps will dip down into the low 30s early in the week, so avoid planting tender seedlings (such as tomatoes). Concentrate on these tasks before or after this week’s rain:

* Fertilize roses, annual flowers and berries as spring growth begins to appear.

* Knock off aphids with a strong blast of water or some bug soap as soon as they appear.

* Pull weeds now! Don’t let them get started. Take a hoe and whack them as soon as they sprout.

* Prepare summer vegetable beds. Spade in compost and other amendments.

* Prune and fertilize spring-flowering shrubs after bloom.

* Feed camellias at the end of their bloom cycle. Pick up browned and fallen flowers to help corral blossom blight.

* Feed citrus trees, which are now in bloom and setting fruit.

To prevent sunburn and borer problems on young trees, paint the exposed portion of the trunk with diluted white latex (water-based) interior paint. Dilute the paint with an equal amount of cold water before application.

* Cut back and fertilize perennial herbs to encourage new growth.

* Seed and renovate the lawn (if you still have one). Feed cool-season grasses such as bent, blue, rye and fescue with a slow-release fertilizer. Check the irrigation system and perform maintenance. Make sure sprinkler heads are turned toward the lawn, not the sidewalk.

* In the vegetable garden, transplant lettuce and kale.

* Seed chard and beets directly into the ground.

* Plant summer bulbs, including gladiolus, tuberous begonias and callas. Also plant dahlia tubers.

* Shop for perennials. Many varieties are available in local nurseries and at plant events. They can be transplanted now while the weather remains relatively cool.

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