Rose black spot?
dandth
16 years ago
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Comments (18)
buford
16 years agochezron
16 years agoRelated Discussions
Joseph's Coat Rose & Black Spot
Comments (3)Both sulfur and copper can burn rose foliage. Be sure the plants are well hydrated and spray in the morning. Don't apply copper on a drizzly day--it is less likely to burn if it dries quickly. Don't use sulfur in very hot weather. I've used the copper soap product Soap Shield successfully. Wear standard PPE when applying copper products....See MoreCleanup important if roses have black spot
Comments (23)I think I found a possible explanation for what I've observed often enough to keep bringing up that I don't strip on the first sign of leaf infection. If this does explain it (or if it's a good theory anyway), then it does seem to have to do with my choice of roses or the aggressiveness (lesion expansion rates) of the local strains of BS here. From http://www.rosehybridizers.org/Fall_2012_Zlesak_long_version.pdf "...We have blackspot resistance field data for the roses that are designated Earth-Kindî in the South Central US. As we correlate the mean lesion size in the lab with the percentage of defoliation due to blackspot in the field, r=0.62...So in this case there is a pretty strong trend that as lesion size goes up for a rose in the lab, the more defoliation we see for that rose in the field. Since different isolates of different races can be more aggressive and lead to different lesion expansion rates, it is very promising to see such a strong correlation in the midst of that variability. As more blackspot resistance data are collected from other ongoing Earth-Kindî trials involving some of these 70+ roses, it will be interesting to revisit the correlation between the laboratory and field data...." And the RHS has seen what I'm talking about, so at least I don't feel so crazy ;) http://apps.rhs.org.uk/advicesearch/Profile.aspx?PID=270 "Typically, a rapidly enlarging purplish or black patch appears on the upper leaf surface, with diffuse and radiating strands of the fungus sometimes just visible. Leaf tissues may turn yellow around the spots and the leaf often drops, even though other parts are as yet unaffected. At other times, the yellow colour does not appear, but infected leaves still drop. Sometimes, the spots remain relatively small and the leaf does not drop. [!]" I'm not trying to tell anyone how to do anything if it goes counter to their local experience, of course. I guess I'm saying that folks might wait a bit and see what happens if they don't strip leaves if the plant will be very defoliated if they did strip so many leaves that don't look too bad. See what happens, perhaps. Or not :) Here is a link that might be useful: Strategies and resources for breeding blackspot resistant roses, DAVID C. ZLESAK...See MoreBare root rose having black spots
Comments (2)Yes, trim off any dead wood. You may lose those early leaves if you get another freeze but the roses should still be OK and leaf out again. If you know it's going to freeze can you move the pot into a garage or shed to protect it some?...See MoreSad Roses - Black Spot and Maybe other issues
Comments (55)louislinus You have a beautiful house. I love your gorgeous stone-walkway. The above pic. (white rose) has a green rose slug. Rose slugs (sawfly larvae) infest roses in poor-drainage clay. You have lots of Walker's low blue catmint, which thrive in heavy clay here. The second pic. (from the top of your post) shows lots of holes in leaves, besides black spots. I also see rose-slug damage (brownish-latticed leaves). Holes in leaves are typical of slow drainage dense clay in heavy rain. I used to get holes in leaves right after heavy rain, then I moved roses and found water could not drain fast in that spot. Roses that like fast-draining like Queen Nefertiti is most susceptible to rose-slug and holes in leaves. I fixed the soil with fast-draining coarse sand, dug out all the rocks below, and NO MORE green ROSE SLUGS. Do you have dense clay soil? If so, then poor-drainage is a problem in mid-west heavy rain. I would check for drainage: dig a hole near the MOST black spotted rose, pour a 5 gallon bucket of water down that hole. If the water doesn't drain within 10 min, any rose would black spot in that area during heavy acidic rain. pH of rain in Midwest area is 4.5. With my 134 varieties of roses, black spot is no longer a problem once I check the planting hole for fast drainage by pouring a 5-gallon bucket of water, before planting a a rose. If the water doesn't drain fast enough, I keep digging and often I would find large stones that block drainage. High Country roses recommend digging a hole 3 feet wide and 2 feet deep. But I often dig deeper than that to check for stones. A quick fix to slow down the heavy & acidic rain is to pile up horse manure (the type with wood-chips, rather than hay). Hay is acidic, but sawdust/woodchips decomposes to alkaline. There's a poor drainage spot where I dug down 2 feet and found water .. but Golden Celebration (black spot-prone) was 100% healthy. I piled up ALKALINE horse manure (with wood-chips) up to 1 feet tall. When acidic rain at pH 4.5 poured down, it was instantly neutralized by that pH 8 horse manure. Stable here deodorizes horse manure with shell lime (high in calcium & high pH). Calcium is the best buffer against acidic rain. The LEACHING of calcium is what causes holes in leaves after heavy rain. Once the leaves are thinned out with acidic rain, they are more susceptible to rose-slugs (green sawfly larvae). I never have rose slugs in the years with horse manure, despite poor drainage clay. In the years of topping roses with horse manure (pH 8), zero black spots in raised beds, and very few leaves with black spots in poor-drainage clay. (posted plenty of pics. in Organic Rose forum). Besides calcium, horse manure has anti-fungal trace elements (zinc and copper) to thicken leaves. Pics below are my roses with horse manure, note the THICKER foliage. Decades ago I saw the same flawless foliage in a neighbor who used horse manure & same with another garden with horse manure. From that time on, I started topping roses with horse manure. I don't spray....See Morechezrondirtface
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