Control Black Spot on Roses

Controlling black spot on roses is crucial to any rose grower. Black spot is a fungal disease characterized by black spots on the upper side of leaves. Tending to occur in warm, wet weather, usually during wet summers, the leaves of infected roses turn yellow and fall off. This weakens the plant by making it more susceptible to other diseases or opening it up to injury for the next winter. The organism responsible for black spot spreads quickly and can move from plant to plant if proper care is not taken.

Steps

Starting with Resistant Roses

  1. Plant black spot resistant roses, as many beautiful rose varieties are resistant to the diseases and fungi. Control black spot by not planting varieties that are prone to it. Maintenance of the resistant varieties is much less than those that fall victim to every rose disease.
    • Specific lists of disease-resistant roses are online, and nurseries likely have their own list. All roses vary by region, so do a local check for varieties that grow best in your area.

Decreasing the Opportunities for Black Spot

  1. Choose rose growing locations carefully. The best tactic to control black spot is to plant roses in locations that benefit the rose and thwart the fungus.
    • Roses should get 6-8 hours of sunlight daily. Morning sunshine is best: it quickly dries out nighttime dew.
    • Growing locations should get plenty of air circulation. Space rose bushes far enough apart to allow for good circulation and prune out some center branches to allow internal air circulation.
    • Prepare the soil well. Ensure that it is rich in broken-down organic matter and that it drains well. Well-rotted compost is a good soil enhancer.
  2. Water your roses appropriately. Excess moisture encourages black spot, so it's important to water with care and to not over-water rose plants. When it's cooler, water weekly with a deep soak at the base. For hot, dry weather, more frequent watering will be required, without wetting the leaves.
    • Use soaker hoses or drip irrigation at the roots of roses for more frequent watering.
    • Take care when watering––black spot spores get moved about by splashing water. Using soaker hoses or drip irrigation is always better than using hoses with spray watering devices.
    • Water roses only in the morning so that the leaves can dry out by nightfall.
  3. Prune regularly. Remove any weak or damaged branches and leaves as part of regular pruning.

Dealing with Black Spot Infestations

  1. Know what you're looking for. Black spot has the following indicators:
    • Circular black spots with fringed margins on the leaves.
    • The lower leaves tend to be infected first, after which it spreads quickly.
    • Upper leaves often turn yellow and fall off.
    • The plant becomes weaker and it either blooms less or not at all.
  2. Remove and place in trash bag any infected leaves and branches as soon as you see signs of black spot. This helps to slow down any further progression of the fungus.
    • Clean up and safely dispose of black spot infected leaves that have fallen to the ground immediately. If left to lie below a rose, the spores of the fungi will start climbing the rose again as soon as the temperature and moisture are right in the spring.
  3. Spray roses every 7 to 14 days with a fungicide during growing months. Even without signs of black spot, this is an important part of good rose preventative maintenance. Fungicides include trifloxystrobin, Ziram, chlorothalonil, mancozeb, Thiophanate-methyl, and several others. For advice on an appropriate spray or powder for your local area, discuss directly with your local garden center.
  4. Prune canes back to wood uninfected by black spot before the growing season. In severe cases black spots can be seen on the stems of the roses. Be sure that these are removed as quickly as they are noticed.

Tips

  • A simple method for working out whether or not roses need watering is to poke your finger into the soil around the base of the plant as far as it will go. If it feels dry, it's probable that the roots need a good soaking.
  • Add a spreader to the fungicide spray to get better coverage on the waxy leaves of the roses.
  • Black spot appears most often in early summer.

Warnings

  • Do not compost rose leaves infected with black spot. The composting process will not kill the fungi and you may be re-infecting your plants. Dispose in the garbage or burn black spot cuttings. Wash all cutting tools with soapy water, then rub down with isopropyl alcohol or similar.

Things You'll Need

  • Fungicide spray
  • Sprayer
  • Spreader
  • Pruning shears

Related Articles

  • Trim Roses

Sources and Citations

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