HELP am I killing my roses or is my neighbor

rosenewbie(z9 CA)May 24, 2004

I recently moved to a home that has 6 rose bushes. 4 of them have black spot. 3 have a mild case and one has a very severe case. On the advice or a nursery, I began the process of removing all the affected leaves. I started with the worst bush and after removing all affected leaves, only 5 leaves remain on the entire bush. I immediately felt a huge amount of remorse, feeling that this couldn't possibly be enough leaves for adequate photosynthesis. This same nursery told me to spray neem oil after removing the affected leaves, but my internet research informs me that neem oil interferes somewhat with photosynthesis, so I'm afraid to use it on this now-fragile plant. I called another nursery which said to do absolutely nothing to this plant until it has more leaves. A third nursery told me to use Bayer systemic on all my plants and the problem will go away. I'm a bit nervous about applying chemical sprays, so I started looking for alternatives on gardenweb which is where I heard about cornmeal usage. It sounded a bit unusual, but certainly the least invasive method I've heard of so far. I've decided that I don't care if my leaves have a few black spots on them. I'm not after perfection. But I do want to save this rose bush and have healthy blooms but I don't want to have to wear a respirator to achieve this state. Any suggestions? By the way, my neighbor waters her bushes in the afternoon with a spray hose and a fair amount of water gets on the rose bushes--could this be what's spreading the black spot? I hate to confront her unless it's absolutely necessary. The nursery said that her watering practices won't harm my roses because black spot is caused by poor soil conditions, so they say that I must improve my aerate my clay soil and fertilize. I'm guessing that I can't aerate the soil until the winter when the plant is dormant and I would then have to remove the plant to do so? Also I drip irrigate them at 5a.m.every day because they are on the same system as plants that need frequent watering--but am I harming the rose bushes by doing that? Your advice before I screw this up even further would be much appreciated.

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Your nursery advice is all wrong. Wet foliage is exactly what allows blackspot spores to germinate and flourish. Research also shows no need to remove the affected foliage, although you will hear that advice all the time. There is no clear evidence that cornmeal will help with BS on roses. There are "soft" methods for control, such as sulfur, the Cornell formula, and others. A search of Gardenweb "Roses" forum archives will provide you with loads of information about this. While a healthy rose will be able to better outgrow disease, a BS susceptible rose will get it no matter what. However, you should be fertilizing your roses throughout the growing season and doing what you can to improve the soil tilth, such as adding compost top dressing. You might consider replacing your roses with more resistant varieties over time if you don't want to deal with controlling diseases. Good luck.

    Bookmark   May 25, 2004 at 12:25AM
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rosenewbie(z9 CA)

I made an error in my original message. My apologies. Someone else in my household is in charge of the watering, hence my error. The roses are on their own irrigation system and are only watered once a week unless you count the unintentional watering that the neighbor gives them. Thank you JAYK for your advice. You said just what I was afraid of--that it wasn't necessary for me to pull the leaves off the plant. I just spent over an hour reading some of the rose forum thread on chemicals to use on black spot and am still (more?) confused. Do you or anyone else have any advice for the rose bush that I pruned almost all the leaves off of (only about 6 leaves left on it now)? Do I use the neem oil my local nursery suggested (and have already purchased)or do I heed some research I did that shows neem oil can interfere with photosynthesis and wait for more leaves to grow before using neem? Or use something else entirely? A relative says he remembers using something many years ago that went in with the fertilizer in granular form and so didn't need to be sprayed and thus limited the safety precautions which I would certainly appreciate if it works. I didn't see anything about this product in the thread on black spot that I read; maybe it was there and I missed it but most of the discussion seemed to focus on commercial sprays. I'll do so more reading tomorrow and see if I can find a reference to it. I'd very much like to save the bush; it was well-established, planted about 15 years ago. I'd rather not be the one to kill it. Thanks.

    Bookmark   May 25, 2004 at 2:54AM
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I think your best approach at this point is to nourish the roses and keep them well watered. Try alfalfa and kelp. Avoid getting foilage wet, water in the a.m. so foilage that might get wet has a chance to dry. Some people, I'm not one of them, have had good luck using cornmeal to prevent and slow the advance of blackspot. Nandina, a respected member of GW, started a popular thread on the Garden Experiments forum about cornmeal/blackspot. You might want to review that thread.

The Cornell Method of blackspot/mildew prevention calls for fine horticultural oil. I don't know if neem oil would interfere with photosynthesis. Field has some good info on neem oil, organic and non-organic rose growing on his website.

Here is a link that might be useful: Field's site

    Bookmark   May 25, 2004 at 7:03AM
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If you want to go organic, the Cornell spray or wettable sulfur are the way to go. Search the archives and you'll find lots of posts on this. Since you are in CA, where blackspot usually isn't much of a problem, you can probably get good control of the situation this way. I agree with the other posts that your nursery was full of bunk. Stripping leaves is not a good idea and doesn't solve the problem.

If you want a simple fertilizer solution, go with Rosetone.

    Bookmark   May 25, 2004 at 8:15AM
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hershigrl(Coastal CA 10)

This time of year, roses usually need more water than just once a week, even on the coast where I am. I would water them at least every other day until you get more leaves.

- HershiGrl

    Bookmark   May 26, 2004 at 7:06PM
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michaelg(7a NC Mts)

Check to see whether the problem is true black spot. Black spot spots have fine fringy margins. Another spot disease is anthracnose, which makes reddish ring spots with gray or tan centers, and there are others. Where are you located? True black spot is rare in many parts of California.

Water on the foliage causes true black spot to spread only if it is continuously wet for 9-12 hours. So a sprinkle doesn't hurt if the humidity is low.

    Bookmark   May 27, 2004 at 2:40PM
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Rosenewbie, don't worry, new leaves will grow back, I have had many a bush loose all its leaves after digging up the bush in mid summer etc... As long as its well watered, a few weeks or a month later, new leaves will sprout.

    Bookmark   May 27, 2004 at 5:01PM
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I have found some small particles in two pots of roses. Within a day, they died. I didn't place those particles in the pot, but I know they were placed there purposely. What could it be and how can I protect them?

    Bookmark   April 13, 2011 at 1:54PM
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