Gambling: do you spray when rain is in the forecast?

9 years ago

Ok, hello folks, I'm back again. So far things were looking better for me. The roses were coming back despite improper winterization, horrible dieback and nasty blackspot.

Well, nothing is ever perfect. Before the humidity struck, I was able to get a good preventative black spot spray in. Following that preventative spray, each time I've sprayed (only twice more), within 12 hours, rain comes out of nowhere and washes it all away.

Since then, any time I make time to spray, it either looks like it's going to rain or the forecast is indicating rain. Right now it looks like it could rain but the local weather is saying that there's only a 30% chance. Would you spray if you were me?

Oh and check out my poor Scentimemtal (photo is below). This is blackspot, isn't it? Whatever happened to floribundas being more resistant to blackspot that hybrid teas? This totally came out of nowhere!

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Comments (3)

dublinbay z6 (KS)
9 years ago
If it rains 12 hours after you sprayed, there should be no problem. It only takes the spray 1-2 hours to dry, and once it is dry, rain doesn't affect it.

Well, maybe I should first ask what you are spraying before I say that. If it is something like Bayer Garden Disease Control for Roses, Flowers, and Shrubs, all it needs is to get dry. Then rain doesn't matter.

If I were getting ready to spray and noticed that the weather report said 30% chance of rain, I would go ahead and spray under most circumstances. A 30% chance of rain means that there is a 70% chance that it won't rain. I don't even let a 40% chance of rain stop me--unless it actually starts sprinkling out there. At 60% chance of rain, I figure the odds are now in favor of the rain--although even then, it may not rain--and I do not spray on that day.

As for your picture, unless you can show me a more detailed, close-up picture showing blackspot, I would say that No, that is not blackspot.

Some of the yellowing leaves could be older leaves which the bush is shedding, making way for young new leaves, or the yellowing could be caused by too much or too little water (either will produce yellowing leaves).

However, some of the other leaves appear to be suffering from RMV (Rose Mosaic Virus)--there appear to be yellow markings on some of the leaves. There is nothing you can do about RMV--in fact, a goodly number of roses on the market are all infected with RMV. Most of us find that the symptoms (gold marks on leaves) only show up occasionally in the spring. Other than that, the rose seems to suffer no problems as a result of the RMV. (There are a few posters who take a different approach to the subject, however.)

Hope that helps.

Kate
michaelg
9 years ago
We would need a sharp closeup of a typical spot to say for sure (blackspot vs other fungal disease), but basically I agree with what Kate said. The yellow veins are a probable virus symptom.

If it doesn't rain for a couple of hours, a fungicide like Bayer tebuconazole will be OK. It is absorbed into the leaf.
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henry_kuska
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The following was stated: " Most of us find that the symptoms (gold marks on leaves) only show up occasionally in the spring. Other than that, the rose seems to suffer no problems as a result of the RMV. (There are a few posters who take a different approach to the subject, however.) "
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H.Kuska comment: PNRSV (apparently the most common rose virus found in the U.S.) is a temperature sensitive virus. At high temperatures the roses' immune system is effective in controlling the virus, at milder temperatures a controlled published scientific study (2007) reported that: "The effect of infection with Prunus necrotic ringspot virus (PNRSV) on growth, flower production and quality of three field-grown rose cultivars: Ingrid Bergman', 'Mr Lincoln' and Queen Elizabeth' was assessed in 2005 and 2006. One and two years after inoculation fresh and dry weight of flowers, diameter of flowers, diameter of shoots, length of shoots, number of shoots, number of flowers and number of flower petals decreased significantly."

This conclusion was consistent with earlier mild climate controlled scientific studies.

http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.element-from-psjc-2c8acda3-1843-304e-89bf-2ad2962af074

Will PNRSV affect the roses in your climate? Unfortunately Zone numbers cannot answer this question. Zone numbers are mainly useful for cold, freezing information. To find high temperature information, take the nearest city of appreciable size and do a Google search of the monthly average high temperatures.

Here is a link that might be useful: summary of high temperature effect information

Gambling: do you spray when rain is in the forecast?

Comments (3)

dublinbay z6 (KS)

michaelg

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