Your roses can be beautiful right up to frost if you maintain constant vigilance with a spraying or dusting program.
How well you keep the foliage and stems protected from September to frost may well determine how old man winter treats your roses, plus the number and quality of blooms you get next year.
Spots Before Your Eyes?
To keep roses presentable to frost —and extract that last gorgeous bloom—several diseases need to be kept in check:
- Blackspot
- Powdery mildews
- Stem cankers
- Rusts
- Spot anthracnose
- Minor leaf spots
Blackspot, known to all rosarians, appears as roundish black spots with feathery margins. Affected leaves turn yellow and drop early.
Plants are weakened, and blooms are reduced in number and quality. Defoliated roses are also susceptible to winter injury and drouth.
Powdery Mildews Thrive Now
Powdery mildews produce whitish-gray, powdery coatings on leaves, flower buds, and young shoots. Cane tips and flower buds may be distorted and killed.
Diseased leaves turn reddish-purple, twist, wither, and drop early. Plants are often stunted with poor vigor and scarce, inferior bloom.
Stem cankers, dieback, and cane blight form a disease complex often confused with winter injury. Cankers usually start as minute white, reddish, or purple spots on the stems.
Stems Dieback
Stems later die back and turn light brown to burgundy or black. Dieback starts from pruning cuts and flower stalk stubs. graft unions, or other wounds. Mature cankers are commonly sprinkled with black dots (fungus-fruiting bodies).
The stems or crowns are girdled, causing the foliage above to wilt, wither and die. Entire plants may die. Cut-rate, undersized roses are usually infected — or dead —when you buy them.
Related: Critical Time of Roses in Spring
Rust Corrupts Even the Rose
Rusts appear in the spring as bright orange, reddish, or orange-brown, dusty pustules on petioles, young shoots, underleaf surfaces, and buds.
Towards fall, the pustules turn chocolate-brown to black and become crusty. Leaves often wilt, wither and drop early. Plant vigor may be reduced in severe attacks.
Anthracnose and Minor Leaf Spots
Spot anthracnose and minor leaf spots appear in various colors, shapes, and sizes on the leaves.
Some have a distinct margin and may drop out, leaving shot holes and ragged leaves. Plants may be defoliated and thus weakened considerably.
To control these diseases, apply a spray or dust weekly throughout the season.
Materials For Effective Controlling Rust
Be sure the material contains phaltan, maneb, captan, or zineb to control blackspot, stem cankers, spot anthracnose, and other leaf spots. Maneb, zineb, ferbam, and sulfur are effective in controlling rust.
Phaltan does double duty, for it controls powdery mildews, also. Other effective mildewicides include Karathane, sulfur, and the excellent Acti-dione PM. Warning: Do not use the last three chemicals when temperatures exceed 85 degrees F.
A bag of multipurpose rose dust or spray needs to contain malathion and another insecticide, such as DDT or methoxychlor, to control insects and mites.
Recipe for All-Purpose Rose Spray
A good combination spray for roses may be made with the following ingredients added to each gallon of water:
- 11/2 tablespoons of phaltan or maneb, 75-80% wettable powder;
- 2 tablespoons wettable sulfur (dry) ;
- 2 tablespoons methoxychlor,
- 50% wettable powder; and
- 3 tablespoons of malathion, 25% wettable powder.
Spraying is more effective than dusting, especially if you are growing many roses. Cover all above-ground parts with each application, concentrating on the underside of the leaves.
Prune out and burn cankered, weak, or gall-like stems as soon as they are found. Make clean cuts three to four inches below the canker and close to a bud.
To prevent spreading infection, dip or swab the pruning knife or shears in 70 percent alcohol between cuts. Cut off and burn old flowers.
Mulching Roses Is Important
Mulch roses throughout the season to prevent water and soil from splashing on the foliage. When watering, avoid sprinkling the foliage. Where practical, collect and burn fallen leaves.
Related: Learn About What Makes A Good Soil For Roses
Local Recommendations By Horticulturist
Space, plant, fertilize and prune plants properly, based on local recommendations as outlined by your extension horticulturist, nearby American Rose Society test garden, a top local rose grower, or a reputable and experienced nurseryman.
Avoid overfertilizing, especially with nitrogen.
Where feasible, grow varieties resistant to blackspot, powdery mildew, rusts, root-knot, and other pests.
Select winter-hardy varieties adapted to your area. Rosarians will gladly help select roses that should do well for you.
Buy only the best-quality, disease-free plants from a reputable nursery. You won’t go wrong with All-America Rose Selection winners adapted to your area.
Many of these magnificent roses have a built-in resistance to several of the most serious diseases.
Protect for winter by following recommended local practices. If in doubt, check with your nurseryman, a successful rose grower, your county extension office, or an extension horticulturist.
- Spray the roses thoroughly just before applying winter protection.
- Apply a dormant spray of liquid lime-sulfur (one part in ten parts of water) before growth starts next spring.
This is a general sanitation spray effective against a wide range of diseases and insect pests.
44659 by Malcolm Shurtleff