Garden dectective: Rose bushes

Published: Saturday, Sep. 8, 2012 - 12:00 am | Page 6CALIFORNIA LIFE

I wonder what has happened to my rose bushes. In the middle of summer, they suddenly developed all these spots on their leaves. Any suggestions?

A Chinese elm has taken over a lot of the yard, so shade has increased for the roses. Did that have something to do with it?

– Anna N. Smith, Chico

After examining some leaves you provided, the UC master gardeners concluded that your roses are infected with the fungal disease called black spot.

More common in other parts of the country, black spot causes dark blotches on foliage and yellowing of leaves. It often spreads during rainy days in spring or summer.

Black spot spreads and reproduces on foliage that stays wet for several hours, so irrigate your plants from the base instead of overhead sprinklers. The shady elm also may have kept damp roses from drying out.

If you hose down bushes to knock off aphids, do it in the morning so the leaves have a chance to dry.

To control black spot, rake up and dispose of all the old leaves and mulch from the rose beds each winter. The fungus can survive many months in the mulch and other garden debris and is just waiting for its wet opportunity to attack fresh foliage.

In winter, prune bushes to allow for good air circulation and keep them uncrowded.

There are a number of products on the market for the control of black spot. Consult your local nursery staff.

Longtime Master Gardener Bill Pierce, who answered hundreds of "Garden Detective" questions before his death in May, had this recommendation for fighting black spot.

"One example that I've had good results with is ImmunoxPlus Insect and Disease Control, manufactured by Spectracide," Pierce said. "It is rainproof and gives protection for two weeks. You'll need to apply the black spot spray you buy at regular intervals in the spring until the rains end."

ImmunoxPlus is available at the Home Depot, Walmart, Target and garden centers.

The University of California also offers advice on controlling common rose diseases and other disorders in its Pest Note No. 7463. For a copy, send a stamped, self-addressed business-size envelope to: PN 7463, UC Cooperative Extension, 4145 Branch Center Road, Sacramento, CA 95827-3823. Or find it online at

After my red crape myrtle bloomed early, I cut the seed pods off. I now have a second bloom. Is this unusual? These are new trees, about 5 to 6 feet tall.

– Neta Athey, Sacramento

When plants are pruned, it usually stimulates growth; that's probably why your early-blooming red crape myrtles put out a second set of blooms, according to the UC master gardeners.

Different varieties (and colors) bloom at different times, according to Pierce, who was "a big crape myrtle fan."

"If several varieties are planted, you can have color from late June through September," he wrote. "I like the red foliage in the fall and their graceful branches and smooth bark provide winter interest."

Crape myrtles are relatively pest-free. Mildew can be avoided by planning for good air circulation or selecting one of numerous mildew-resistant hybrids.

"They surely are well suited for the Sacramento region," Pierce said.


Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h& Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned

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