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

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.

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

Personally, if the forecast says only 30%, I usually go ahead and spray. Unless the sky looks really threatening, there's a decent chance the spray will have enough time to dry and do its thing. I’ve been burned before by putting it off and then dealing with a full-on blackspot outbreak that takes weeks to manage. I’ve also noticed floribundas can be just as sensitive some years if the weather's really working against you, so I don't take chances anymore.

When I’m doing anything that involves timing and chance, like spraying before possible rain or even playing online games, I usually try to check resources that help weigh the odds. I actually used Bonus Burst in the past to compare online casino bonuses, kind of the same vibe of trying to make the smartest call with the highest reward.