Can anyone tell me what is going on with my Knockout Roses?
by
P
+14
They have a white powdery substance on some of the leaves and the buds and blooms are malformed. They have developed an overgrowth of thorns. If this is a disease process, can it be treated and how? Thank you all in advance for your input.
10 answers
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Powdery Mildew lots of cures if you google Powdery Mildew
Meg Wylie
on Sep 22, 2013
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1 Teaspoon Baking Soda to 1 quart water I add a TBSP of cooking oil to help the baking soda stick to the leaves! Spray all the leaves of your knockout Roses, also raise the acid content of your soil Epsom Salts at the base of your stems and or used coffee grounds around your roses!
Meg Wylie
on Sep 22, 2013
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From the pics I see gnarly stems happening? If this is what you are talking about it is Rose Rosette disease which has been hitting Knockouts this year. It is caused by a virus and it will spread fast by going internally and killing the roses and spreading to others. You may be able to save this and others by pruning the rose back quite a bit and clean up any debris around the rose. Good luck
The Garden Frog with C Renee
on Sep 22, 2013
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Yes, there are gnarly stems happening. I think this may be what it is. However, I haven't really seen the red stems...they are more silver gray in appearance, but all the other characteristics are there. I am wondering if I have 2 different disease processes taking place on them...both the Rose Rosette and Powdery Mildew. From the looks of my plants and what I have read I am doubtful I will be able to save them.
P
on Sep 22, 2013
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Agree with C Renee. That is Rosette, however, looks like it's just starting. So you have a good chance of saving the plant. Cut it back by at least one-third. Be sure to keep your pruners sterile!! (1 pt bleach to 9 pts water) then use a fungicide. The baking soda and oil is a good organic fungicide to use. In the spring, add rich organic materials to your bed. Avoid commercial chemical fertilizers as they kill off the microorganisms in your soil. Good soil health leads to healthier plants with can better withstand disease and insect pests.
Catherine Smith
on Sep 23, 2013
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Rose Rosette disease is carried by a very small mite that carries the virus. It is an airborne mite that carries the virus not through the soil or garden tools (even though you should clean your pruners after you cut any diseased plant) except if the infected plants is not removed and roots remain. I HAVE SAVED Knockouts with this disease and if you catch it EARLY, you can save the plant. The virus stays in infected leaves for a couple weeks and then travels down the stem. You should also use a miticide to kill the mites which have a cycle of 7-14 days. Closeness of roses can spread this virus and roses need room to have air flow. Cut back your roses every winter to keep the mites under control. http://www.greenhousegrower.com/video/c:271/webinars/1454/ This is a very informative webinar about the disease and precautions, control, and eradication. horticultural oils and miticides are explained. It is about an hour webinar with Q&A at the end. the symptoms your rose is also displaying could be from using an herbacide. So another question is if you have sprayed any weed killer around your roses that could have blown onto the plant?
The Garden Frog with C Renee
on Sep 23, 2013
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No, we have not sprayed anything this year at all. No herbicides, pesticides or otherwise. I have 2 bushes and over the course of the last 4 years they have grown significantly and grown together.
P
on Sep 23, 2013
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Our extension office says that if you have Rosette, dig up the plant, bag it, and throw it in the garbage. Do not compost or keep the roots in the ground. Since you have received a wide variety of advice, I would suggest that you do your own research on Rose Rosette and make your own decision.
Gretchen
on Sep 24, 2013
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A couple years ago my sister-in-law had a huge knockout that all of a sudden hers started doing the same thing, she had no choice but to cut it down, and dig it up.
Patty
on Sep 24, 2013
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Several months ago another member of HT asked he same questions. Several answered that it was "Rose Rosette disease" for which there is no cure but to dig it up and not plant another rose in the same spot. So sorry.
Liliana Wells
on Sep 25, 2013
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