problem solver

Rose rosette disease

IDENTIFICATION — Rose rosette is caused by an organism similar to a virus that’s transmitted by mites. Although you usually find it in weedy multiflora rose, all roses are susceptible. And it’s becoming more common in cultivated ones.

Symptoms include increased thorniness, small red or purple leaves and rapid, dense growth of the shoots in “witches brooms.”

CONTROL — Unfortunately, there’s no cure for rose rosette disease. If you think your rose has it, remove and send it away in the trash to prevent infecting others. Get rid of any nearby stands of multiflora rose, as well.

plant pick

Graham Thomas rose
Rosa ‘Ausmas’

Talk about romantic roses! The richly scented, voluptuous yellow blooms of Graham Thomas are the very definition of romance. Fully double, 3 1/2-in.-diameter flowers form in clusters on arching canes, leaving behind large yellow hips in fall. The effect is mesmerizing!

Graham Thomas has the upright, bushy habit typical of shrub roses. It usually grows to 3 to 6 ft. tall, but in warmer areas where it doesn’t die back in winter, the plant can reach 10 to 12 ft. tall.

Space plants for good air circulation, water deeply near the soil and add mulch to hold in moisture and discourage weeds. Remove faded flowers and fallen leaves to keep the plant tidy and to prevent disease.

TYPE Shrub rose SIZE 3 to 12 ft. tall by 2 to 4 ft. wide BLOOM Yellow flowers from early summer to fall LIGHT Full sun SOIL Moist, well-drained PESTS Blackspot and Japanese beetle are occasional problems HARDINESS Cold: USDA zones 5 to 9; Heat: AHS zones 9 to 1

Want to learn about more great shrub roses? Check out Issue 91 of Garden Gate magazine, on newsstands now!

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problem solver

Rose slug sawfly
Endelomyia aethiops

IDENTIFICATION — Smooth, translucent pale-green larvae could attack the leaves of your roses next May and June.

DAMAGE — Feeding on the surface of the foliage between the veins, larvae create a window-pane look. Leaves turn brown and curl. Large infestations may stunt the plant’s growth.

CONTROL — Prune out or handpick small populations. On cloudy days (so you don’t burn the leaves) in early summer, spray all plant surfaces with Safer^® insecticidal soap or horticultural oil to smother younger larvae. These controls don’t work as well on older larvae, but most of the damage has already been done by then.

If there are so many larvae that the plants stop growing and blooming, dust the affected plants with an insecticide containing carbaryl, such as Sevin^®. Or dilute and spray spinosad on all leaf surfaces in early summer. And all season, pick up debris and leaves from around plants to remove any larvae that may be hiding there.

Learn the secrets of helping your grafted roses survive the winter. It’s easier than you think. We’ll share tips on how and when to cover them so you’ll enjoy beautiful blooms next year.

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problem solver

Blackspot on roses
Diplocarpon rosae

IDENTIFICATION – The name says it all. This fungal disease causes black spots with fringed margins and a yellow halo on leaves. Infected leaves drop early, often leaving the plant almost bare. Blackspot doesn’t kill roses, but it weakens them, making them susceptible to insects, cold and other diseases. Warm, humid summers make blackspot worse.

CONTROL – The best control is prevention: Plant blackspot-resistant varieties. Ask at your local garden center which ones are best. Make sure roses have good air circulation and full sun, and water with a soaker hose. If you use overhead watering, water in the morning so the leaves dry quickly. Rake out fallen leaves around the plant to get rid of as many spores as possible. You can’t get rid of the spots already on leaves, but you can prevent more from forming. Spray your roses with a mix of 1 tablespoon baking soda and 1 tablespoon horticultural oil in 1 gallon of water once a week if you see signs of blackspot. Shake the sprayer to keep the mixture stirred and spray until all the foliage is coated. Try this on a few leaves first, to make sure it doesn’t burn them. If it does, use less baking soda. Neem oil is also effective. Spray on cloudy days or early morning, not in full sun, to avoid burning the leaves.