Rose Diseases Require Moisture, Mild Temperatures; Ginger Loves Sun | Print |  E-mail
Thursday, 08 November 2012 16:45

110812re2By Buzz Bertolero

The Dirt Gardener

Q: When my gardener cuts back my rose bushes, can I spray an anti-rust agent onto them? Will this help hinder diseases next summer?

A: Yes, it is recommended that roses be sprayed once with a copper spray or dormant oil after pruning. If they have buds and blooms, I’m not so sure I’d prune them now. Roses do bloom year round, so enjoy the color even if the foliage looks bad.

When pruning early, it’s not necessary to spray right away. However, I’d wait until the end of January and spray at that time.

You should strip off all the remaining leaves and clean up all the debris from around the base of the bushes before spraying.

Rose rust, black spot and mildew will overwinter on the rose canes, the old leaves and other debris. Good sanitation practices are important in the controlling of these diseases, along with dormant spray; however, they will not prevent the disease, just help them from reoccurring next spring and summer.

Rose rust, black spot and mildew are airborne funguses that require moisture and mild temperatures for them to be a problem. So, once the rainy season concludes, it’s critical the foliage remain dry after the sun goes down. Avoid getting the foliage wet late in the afternoon.

Rose rust requires only two to four hours of constant moisture for the infection to begin. With black spot, it’s seven hours; hence, rose rust will always appear before black spot.

Mildew is present with temperatures in the mid 60s or above and moist conditions. In March, it makes sense to apply a systemic rose disease control after the new growth is about a half-inch long. Besides treating the fungus, it also feeds the plants and controls aphids. These products provide six weeks of protection with one application, as the rainy season concludes.

One final note: Disease-resistant rose varieties and disease control sprays are not the end-all solution to these problems. With the right conditions, Rose Rust, Black Spot and Mildew will inevitably appear.

Q: I bought a home and planted several yellow and white ginger plants from the Big Island of Hawaii about five years ago. They’re in the ground most of the year; but, when winter approaches, I put them in pots and bring them inside. Why don’t I get any flowers? My neighbor across the street from me gets flowers, but his plants get quite a bit more sun. I’m using a fertilizer that is high in phosphorus and potassium and low in nitrogen.

A: This is a tale of two locations — one favorable and one that’s not so.

Ginger is a sub-tropical plant, so the location is important in the Bay Area. They need a warm, sunny or very bright location to bloom. They don’t flower in a low-light area.

With our mild summers here in the Bay Area, this is particularly important the closer the location is to the water. Next year, you should look for a sunnier location.

Buzz Bertolero is Executive Vice President of Navlet’s Garden Centers and a California Certified Nursery Professional. His web address is and you can send questions by email to This e-mail address is being protected from spambots. You need JavaScript enabled to view it or to 360 Civic Drive, Ste. “D,” Pleasant Hill, CA 94523, and on Facebook at



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