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Knowing how to control black spot on roses is an important weapon in a rose grower's arsenal. Black spot is a fungal disease characterized by the appearance of black spots on the upper side of the leaves. It tends to occur in warm, wet weather, usually during a wet summer. The leaves of an infected rose will turn yellow and fall off, weakening the plant and making it more susceptible to other diseases, or opening it up to injury during the next winter. The organism responsible for the unsightly spots spreads quickly and can move from plant to plant if proper care is not taken to control black spot on roses.
Starting with Resistant Roses
- 1Plant black spot resistant roses. There are many beautiful rose varieties that are resistant to the diseases and fungi that have been the bane of rose growers in the past. One of the simplest means of controlling black spot on roses is to not plant those varieties that are prone to getting black spot. The overall maintenance of the resistant varieties is much less than those that fall victim to every rose disease and fungus that blows in on the wind.
- Specific lists of disease-resistant roses will be found online; just do a quick search. And possibly your local nursery has even produced its own relevant list (check its website or call the nursery or garden center direct). The rose varieties will likely vary by region and country, so it makes sense to do as local a check as possible for varieties that grow best in your area.
Decreasing the Opportunities for Black Spot
- 1Choose your rose growing location with care. One of the first tactics of controlling black spot on roses is to plant the rose in a location that is beneficial to the rose and unfriendly to the development of fungus.
- Choose a location for your rose plants that gets 6 to 8 hours of sunlight each day. Morning sunshine is best for roses, it dries out the nighttime dew faster.
- Ensure that the growing locations gets plenty of air circulation. This includes spacing rose bushes far enough apart to allow for good circulation and pruning out some of the 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.
- 2Water your roses appropriately. Excess moisture encourages the growth of 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. However, this should be done without wetting the leaves.
- Use soaker hoses or drip irrigation at the roots of rose plants for more frequent watering.
- Water rose plants only in the morning so that the leaves have a chance to dry out.
- Take care when watering––spores of black spot get moved about by splashing water. This is why soaker hoses or ground irrigation is always better than using hoses or spray watering devices.
- 3Prune regularly. Remove any weak or damaged branches and leaves as part of regular pruning.
Dealing with Black Spot Infestations
- 1Know what you're looking for. Black spot has the following indicators:
- Circular black spots with fringed margins can be seen on the leaves.
- The lower leaves tend to be infected first, after which it spreads quickly.
- Upper leaves often turn yellow and will fall off.
- The plant becomes weaker and it either blooms less or not at all.
- 2Remove infected leaves and branch areas as soon as you see signs of black spot infestation. By removing the leaves with black spot infection on them, you help to slow down any further progression of the fungus.
- Remove dead, 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 a soon as the temperature and moisture are right in the spring.
- 3Spray the plants every 7 to 14 days with a fungicide during the growing months. Even without signs of black spot, this regular form of protection 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.
- 4Prune 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.
- Black spot shows up most often in early summer.
- Add a spreader to the fungicide spray to get better coverage on the waxy leaves of the roses.
- Do your roses need watering? A simple method for working out whether or not they need watering is to poke your finger into the soil around the base of the rose plant as far as it will go. If it feels dry, it's probable that the roots need a good soaking.
- 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.
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- http://www.extension.purdue.edu/extmedia/BP/BP-139-W.pdf – research source
- http://ohioline.osu.edu/hyg-fact/3000/pdf/3072.pdf – research source
- http://umaine.edu/ipm/ipddl/publications/5097e/ – research source
Recent edits by: Wikihow4eva, Leona
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