Fungi Turn Garden Hopes From Rosy to Disappointing

— Written By and last updated by Diane Lynch

Q: It looks like my roses have a disease. What is it and how can I control it?

A: Roses are a popular plant known for their large, elegant flowers. Many gardeners try their hands at growing roses in gardens and landscapes. Poor disease control is one of the most common problems with roses. Black spot and powdery mildew are important diseases to be aware of when growing roses.

Black spot is the most serious disease of roses in North Carolina. Black spot is a fungal disease that causes circular black spots with a frayed margin on the upper leaf surface. These black spots start small and will enlarge and increase in number. Eventually the infected leaf will turn yellow resulting in premature defoliation. If no action is taken to control the disease, defoliation will continue which will weaken the plant and reduce flower production. These weakened plants will become much more susceptible to other diseases and to winter injury. Black spot spreads from leaf to leaf during wet periods and new spots develop in 5 to 10 days.

Black spot has to be controlled in order to grow healthy roses. Black spot cannot be adequately controlled without a good spray program. Do not let the disease build up before starting a spray program. A complete uniform spray on both sides of leaves is necessary. Spray applications must begin as new growth starts in the spring and continued at 7 to 10 day intervals and after heavy rains for the entire growing season. If the disease occurs, immediately remove infected leaves from the rose garden as they appear and rake up and/or discard old fallen leaves during the winter months. During the winter, remove all leaves from the plants and discard. In the fall prune hybrid tea roses to about 18 inches and destroy the prunings. In the spring, prune again to about 10 to 18 inches and destroy the prunings.

Powdery mildew is a very common fungus disease on roses. Powdery mildew is evident by the white mold that occurs of the surface of young leaves, shoots, and flower buds. The disease causes leaf distortion but less leaf drop than black spot causes. Powdery mildew is usually more severe in shady areas and during cool periods. The fungus is windborne and can increase during periods of heavy dew. The diseased foliage and canes should be removed and destroyed during the growing season along with following a fungicide spray program.

There are several fungicides that can provide control of black spot and powdery mildew. A recommended spray program includes the use of chlorothalonil (Daconil) and alternating with one of the following three fungicides: triforine (Funginex), propiconazole (Banner Maxx), or myclonbutanil (Immunox, Eagle, or Systhane). Spray applications should be made every 7 to 10 days. Remember when spraying to completely cover all plant surfaces for best results. Read and follow all label directions when using fungicides.

If you want roses in your landscape but don’t want to deal with a spray schedule, there are some options. New rose types continue to show up on the market that is disease resistant. One of the most popular rose types that have disease resistance is the popular Knock-Out roses. When shopping for roses, be on the outlook for disease resistant types and you can avoid being as dependent on pesticides but yet can still have beautiful roses in your landscape.

For your gardening, landscape, and lawn questions contact the Wayne County Extension Master Gardener Volunteer Plant Clinic on Mondays and Wednesdays from 10 am to 1pm. The plant clinic is a free service open to any citizen in Wayne County that has home gardening questions. One can reach the Wayne County Extension Master Gardener Volunteer Plant Clinic by phone at 919-731-1433, e-mail at Master.Gardener@waynegov.com, or stopping by Room 100 of the Wayne County Extension Office (208 West Chestnut Street, Goldsboro). People contacting the plant clinic with questions are encouraged to bring samples and/or pictures that could help in reaching a solution. Extension Master Gardeners are trained volunteers with the Wayne County N.C. Cooperative Extension Service.

Recommendations for the use of chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services does not imply endorsement by the North Carolina Cooperative Extension Service nor discriminated against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent from North Carolina Cooperative Extension Service.

Upcoming Local Gardening Events:
• We are now on Facebook ! “Like” us on Facebook to receive timely garden tips, ask questions, and find out about upcoming events. Go to: www.facebook.com/waynecountygardening

• Gardening 101 Workshop Series in June! The Wayne County N.C. Cooperative Extension Service will be holding a Gardening 101 Workshop Series in June. This workshop will be three sessions on Saturdays, June 15, 22, and 29 from 9 am to noon at the Wayne Co. Extension Office at 208 W. Chestnut Street, Goldsboro in the Wayne Center. This free workshop is open to the public to learn the basics of gardening whether its for a landscape, lawn or vegetable garden. Session 1 will cover basics of plant selection and plant care. Session 2 will cover soils and fertilizer, while session 3 will be on managing pest problems. Pre-registration is required by June 12th. Please call the Wayne Co. Extension Office at 919-731-1520 to register. Call soon to register because the class minimum is 20 and maximum is 50. The workshop will be presented by Jessica Strickland, Wayne County Horticulture Extension Agent.

NCSU & NC A&T University commit themselves to positive action to secure equal opportunity regardless of color, creed, national origin, religion, sex, age or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.

Jessica Strickland
Extension Agent
Horticulture
North Carolina Cooperative Extension
Wayne County Center
P. O. Box 68
Goldsboro, NC 27533
E-Mail: jessica.strickland@waynegov.com
Phone: 919-731-1525
Fax: 919-731-1511
https://www.ces.ncsu.edu/wayne

Written By

Photo of Jessica StricklandJessica StricklandExtension Agent, Agriculture - Horticulture (919) 731-1521 (Office) jessica_strickland@ncsu.eduWayne County, North Carolina
Posted on Jun 5, 2013
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