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What to expect after treating black spot

Posted by sara82lee 8a - SE Va (My Page) on
Sat, May 24, 14 at 12:27

I feel plagued by fungus :( Last year I had a hydrangea that got a bad case of cercospora that completely defoliated it for the remainder of the year. I feel like I have finally gotten a handle on that and have prevented it from returning this year (so far!), and the hydrangea looks very healthy again. However, after the cercospora it seemed fungus started popping up everywhere last year - from a very sturdy hawthorn to some annuals growing in pots. Ironically it seemed the healthiest plants were the most affected. This year I committed myself to do everything possible to fight back - and things are much better so far.

But I didn't anticipate issues with my roses. They were newly planted last year as bare roots. This year they seemed to come back strong and are currently covered in huge blooms! However, after some heavy rain, now all but one is covered with black spot. In some ways I feel like I know what to do to keep it from spreading, after learning how to handle the cercospora. . . as far as treating the bushes and cleaning things up, how to water, etc. But will the bushes lose all of their leaves? Should I really pick them all off? The largest two have spots on every leaf. If I remove all of the infected leaves, there won't be any left.

Follow-Up Postings:

RE: What to expect after treating black spot

How did you treat the hydrangeas? I'm afraid in the southeast, blackspot is a fact of life on roses. They almost all get it eventually. What I find the most effective is the Bayer Advanced disease control. It's best used as a preventative, but if you apply it now, it can stop the fungus from spreading even further. You don't have to remove the leaves, they will fall off eventually. But most likely they roses will put out more leaves. But you will have to start a spray program of at least every 2 weeks over the summer.

RE: What to expect after treating black spot

Bayer Disease Control for Roses etc, a spray concentrate containing only tebuconazole, will kill the blackspot inside the leaf. The leaf will survive if the spots on it were only a week or so old. However, more mature blackspots will have damaged the leaf irreparably. The leaves will drop and new leaves will appear. If you keep those protected with fungicide, they will last all season. With active infections, I would apply tebuconazole twice at a 7-day interval, and thereafter at 14-day intervals. If it is extremely hot and dry, you can skip a turn.

What product are you using (exact name, please)?

Most other fungicides will not kill the fungus inside the leaf, but will protect against new infections.

RE: What to expect after treating black spot

Hmmm, the Bayer products are good? Last year I used the Bayer 3 in 1 granules once a month, which has the tebuconazole in it:

This year I didn't see that same product so I just picked up their 2 in 1 product instead - doesn't have the disease control:

Sounds like I should have looked harder for the 3 in 1.

I will look for the products you've listed. I'm glad to hear that they should put out new leaves!

For the hydrangea, I've been using a combination of two products, actually mixed together, as recommended by my local garden center: fertilome horticultural oil with a bonide fungicide. She said the idea is that the oil will help the fungicide to not wash off and that it has antifungal properties of its own as well. It seems like a lot to me, but I sprayed with Daconil last year up to every other day and it did virtually nothing. I'm hoping that after this year I can back off a little with so much spraying?

I really appreciate your advice!

This post was edited by sara82lee on Sat, May 24, 14 at 13:48

RE: What to expect after treating black spot

No, no--please don't buy the combination products. Warning: the insecticide in Bayer 2-in-1 is extremely dangerous. I would never use it.

Buy the fungicide spray concentrate "Bayer Disease Control for Roses, Shrubs, and Flowers." You may need to get it online. It needs applying only every two weeks. I don't know it it would work on the unknown hydrangea disease. Sound like you have a bad variety of hydrangea for your climate. These normally do not need spraying.

Bonide Fung-onil is the same chemical as Daconil. (chlorothalonil).

RE: What to expect after treating black spot

what Michael said, please!!

RE: What to expect after treating black spot

Oh dear. I'm very glad I asked here. No more Bayer combo stuff then. I don't even really think I need the insecticide. I don't have much of an issue with insects for the most part. I don't want to use something that is harmful on top of being unnecessary.

My hydrangea isn't anything terribly exotic - just some unknown endless summer variety that was here long before I ever moved in. It was always healthy before last year. So I don't know. But what I'm doing with it now seems to be working well, so I'll keep up with that.

Thanks again to everyone. I really appreciate what you've shared.

RE: What to expect after treating black spot

  • Posted by seil z6b MI (My Page) on
    Sat, May 24, 14 at 18:50

Besides the insecticide being toxic stuff you don't need all those other products. If you don't have a specific insect infestation why spray for bugs? There are specific insecticides for specific bugs and you could be killing off some of the beneficial bugs that help control the pesky ones which could lead to a worse pest problem down the road. I presume you fertilize you plants regularly so why add that to your spray program too? Just use the proper thing for the specific problem you have at the moment and don't add stuff you don't need.

RE: What to expect after treating black spot

Daconil will work as a preventative, but it won't save leaves already infected.

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