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my sister sent me these three pictures of her neighbor's Knockout Roses. she wanted my opinion on the problem but i would like to hear from people on this forum before i talk to her again.
the roses are in st.louis, missouri. they have had a lot of rain, a very mild winter by their standards, cool temps then really hot ones interspersed. my sister says there are no webs or evidence of spider mites or any other pest. i'm leaning towards some kind of fireblight but i really just don't know.
any comments are appreciated.
Just found this thread so I'm throwing in my two cents worth of ideas.
Three things come to mind, but not in any specific order:
1.) Possible damage from overspray from a weed killer like Roundup ???
2.) Fertilizer burn ??? (Too much nitrogen ???) Am leaning towards this one.
3.) You mentioned they had a lot of rain and then heat spells alternately...I've had that happen when it's been really rainy and then a week or more of heat...the new growth (or all of it for that matter) seems to burn up due to the extremes.