Foggy conditions prompted recent outbreak
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| Gray mold, also called botrytis, ruins rose blooms. (Photo: Debbie Arrington) |
Gray mold has me feeling blue. I love autumn roses. Hundreds of rosebuds in my garden had me envisioning fresh bouquets this holiday season.
But most of these November roses will never open. Instead, they turn to mush on the stem.
The reason? Gray mold. That’s the descriptive nickname of the fungal disease botrytis. It’s common in November rose gardens, and this season’s outbreak looks particularly yucky.
Rain storms in early November kicked it into full gear. Recent foggy conditions nurtured its rapid advancement.
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, keep flower buds dry. That’s all but impossible on damp, foggy days.
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.
Gray mold 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 gray mold 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. After pruning when roses are dormant, 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 with fresh mulch.
For more information on gray mold, check out these pest notes from UC IPM: http://ipm.ucanr.edu/PMG/r280100511.html
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Garden Checklist for week of March 16
Make the most of dry breaks between showers. Your garden is in high-growth mode.
* Pull weeds now! Don’t let them get started. Take a hoe and whack them as soon as they sprout.
* Prepare 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.
* Feed roses with a balanced fertilizer (such as 10-10-10, the ratio of nitrogen, phosphorus and potassium available in that product).
* Prune and fertilize spring-flowering shrubs and trees after they bloom. Try using well-composted manure, spread 1-inch-thick under the tree (but avoid piling it up around the trunk). This serves as both fertilizer and mulch, retaining moisture while cutting down on weeds.
* Cut back and fertilize perennial herbs to encourage new growth.
* In the vegetable garden, transplant lettuce and cole family plants, such as cauliflower, broccoli, collards and kale.
* Seed chard and beets directly into the ground. (To speed germination, soak beet seeds overnight in room-temperature water before planting.)
* Before the mercury starts inching upward, this is your last chance to plant such annuals as pansies, violas and primroses.
* 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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