Home Garden
# Home & Garden >> Plants, Flowers & Herbs >> Growing Roses

When to Spray Roses for Blackspot

Blackspot is one of the most common and pervasive diseases of roses in the U.S. If untreated, it will weaken or kill affected roses. As a fungal disease, blackspot develops and spreads because of a number of specific factors, including climatic conditions. A combination of site selection and the application of properly timed disease-specific fungicides will help to control blackspot on roses.

  1. Symptoms

    • Blackspot most often occurs during the warmest summer months.

      As the name implies, blackspot causes round black spots on the leaves of roses. It usually first appears on the upper surfaces of rose leaves, but occurs on the undersides, as well. The spots have irregular margins and often merge to form blotches on the leaves. The remainder of the leaf will turn yellow and drop if untreated. Occasionally blackspot will appear as a reddish hue with purple to black lesions on the stems.

    Conditions for Development

    • Like other fungi, blackspot spreads by spore distribution.

      Blackspot develops when rose leaves are actively growing. Temperatures between 72 degrees F and 86 degrees F are the prime range for blackspot. A period of 7 hours of continual moisture on the leaves sets the stage for the disease to develop and thrive. Spores of blackspot can easily travel from leaf to leaf by splashing water either from rain or irrigation. Roses that are compact and do not have proper air circulation between the leaves also contribute to the disease.

    Sprays

    • Sulfur sprays are a centuries-old remedy for fungal diseases on plants.

      A variety of preventative and control sprays are effective for combating blackspot. Fungicides containing one or more of several ingredients, including captan, chlorothalonil, mancozeb and copper-sulfate, are effective when applied to susceptible roses at the time of bud break and then twice per month until the rose leaves have fully developed. Applications during the growing season should occur every 7 to 14 days. To avoid the disease developing a resistance to a particular fungicide, it is advisable to rotate applications among sprays containing different active ingredients.

    Prevention

    • A soaker or drip hose not only uses water more efficiently, but helps reduce the incidence of disease.

      To prevent blackspot on roses, start by selecting disease-resistant varieties. Do not allow any fallen, diseased leaves to decompose into the soil. Remove and destroy any infected leaves. Pruning rose canes in winter before new growth appears and altering your irrigation practices can help to prevent blackspot. Do not water overhead; instead, water at soil level so that rose leaves do not get wet. Moisture on the leaves that does not evaporate contributes to the development and spread of fungal diseases like blackspot.

Previous:

Next:

Growing Roses
  1. When to Pick Mint Leaves for Tea?
  2. When to Spray for Clovers in the Spring
  3. Home Remedy for Aphids Spray for Roses
  4. When to Prune Roses for a Specific Bloom Date?
  5. Home Remedies for Killing Bugs on Roses
  6. Home Remedy for Aphids Spray for Roses
  7. Remedies for a Fungus on a Rose Bush
  8. When to Spray Roses With Spinosad for Sawfly
  9. When a Rose Bush Is Losing Leaves
  10. The Best Homemade Spray for Black Spots on Roses
  11. When Is the Best Time to Spray Roses?
  12. What Causes Roses to Get Black Leaves?

Home Garden © https://www.98905.com