The nursery news proclaimed the Knockout was the disease resistant answer to growing roses.
And it was, for a while…
The Knockouts are not disease resistant and when it comes to the destruction of Rose Rosette disease, I find first hand that the Knockout goes down with a fight…
I have also discovered after 3 years of growing Knockouts, that they are not as invincible as the garden centers want you to believe. Now I am not saying “do not buy them” but I am giving you warning that they are not as carefree as you have been told. They need pruned to keep their shape in many gardens and the tag may read 3-4′ but that means in a season (here in zone 7). If you have a part sun area that receives morning sun, then the Knockout will perform and bloom but pruning to retain a compact shape is necessary- otherwise the plant tends to get a bit leggy. As long as the Knockout gets about 6 hours of sun, you can get it to perform. I have seen it perform mediocre in dappled shade. It is truly an adaptable rose but it is not without its problems.
Rose Rosette disease-the symptoms of death.
I have saved one of my Knockouts twice now in 3 seasons by pruning the infected branches past the obvious signs of disease at least a foot. The disease was limited to 2 branches and for the growing season of 2013 the Knockouts had grown to over 5 1/2’h x 4’w bloomed beautifully with no signs of the disease. In late November while I was raking leaves and listening to my husband say those roses are too big in front, I decided to whip out the pruners and cut it way back to the ground so that it would grow fuller and reach its 4′ height. The weather here in VA is still warm enough where the roses still had some leaves and sporadic blooms so I left it prune until December when the weather I knew would be cold enough to kill any bugs that could cause harm. So in December I went out to prune the Knockouts to find them literally covered in white flies and aphids! So I cut the Knockouts way down to about 6″ above the ground and coated them with my arsenal of natural pesticides since I knew the weather was going to turn cold. Plus I knew the Rosette disease was spread by the very tiny eriophyid mites so I was not too concerned since the Knockout had shown no signs of the disease.
April 2014 the Knockouts start to emerge and they were looking good and by the middle of May the blooms were setting on the 2 foot high plants and I was ecstatic that they were looking so good. Then I mowed on Monday and noticed that the new growth was a beautiful burgundy color and I knew…
It had spread full blown to all 3 of the Knockouts and so I initially thought that it was contained to a couple stalks and that when I had time in a couple days I would cut them down again. I waited too long…Today I took off to do my own gardening and the Knockouts were all emerging with new burgundy shoots and the telltale witches broom thorns. I could not believe that in 4 days my roses the disease spread that fast.
Since some jokingly refer to me as the plant whisperer, I thought I can save these as long as the disease is not too far gone. I am a saver and so I have to try. I grabbed my pruners, the rubbing alcohol to clean my pruners in between each cut, and an empty dog food bag to gather the infected stems. I started with high hopes since I had saved the Knockout before but my hopes quickly sank as I realized that the infection had hit all 3 and telltale signs of the disease went all the way down to the old cane. I still cannot admit defeat. I have saved plants from the dump with most of their roots gone and I have even saved plants from dumpsters but nothing prepares you to dig up and throw away 3 plants that were big and beautiful just last season.
Identifying the telltale signs of this disease, which can easily be overlooked, because new growth on Knockouts and other roses can be red. I hope the pictures show that the color of the new growth emerges as a beautiful deep red almost burgundy color and the leaves do not appear to have any deformities. However, upon further inspection you will see very large thorns and then a bunches of small or even larger thorns appearing in clusters (which is known as witches broom). I also include the pictures to show you that the thorns of the infected canes are also red in color and the older leaves are tinged in red. This disease can happen in days and as I have written it took over all 3 of my plants in less than 4 days!
From this blog I hope to educate you on what to look for and take quick action to remedy any bug or disease infestation you may have. What bothers me the most about this lesson…I do walk around my beds and inspect on a weekly basis and am vigilant about watching for signs of distress and disease and usually I take immediate action. I was not able to this time and now I have to dig up 3 well established Knockouts and watch the others closely.
But there is good news…I now have a place to plant some more hydrangeas.
I still believe if you catch this disease early you can save the plant but I know you must be very careful about what the consequences are if the attempt fails. I hope anyone reading this takes the time every time you mow the lawn to walk and check your plants and be watchful for any signs of pest and disease. Happy Gardening!
Update as of June 9, 2014
Lost another Knockout in another area but in the front yard and it has affected my climbing rose about 30 feet away. I have 1 left in front and 3 in the back yard so far not affected. I am making the decision to remove all Knockouts when I find a replacement for them and will carefully watch my rescue roses for any signs.
I have also come to the conclusion that any disease may affect Knockouts who have been distressed before planting. I bought mine all on the clearance racks and have had to battle pests and disease. The Rose Rosette disease is a virus spreading from the Phyllocoptes fructiphilus, a microscopic mite, which is carried by the wind and feeds on the roses. Many of the sources say that the disease is spread via the root systems of the roses-which I believe only to partially true. I believe if the mite is carried by the wind, then this should also be classified as an airborne disease as well since it is carried by the mites to each rose. My hypothesis comes from my own experience wherein I have other roses not in the same area affected. So no rose is safe if one rose has become infected in a garden or area.
Just my opinion…
So my thoughts would be to apply a preventative insecticide to your roses and keep a vigilant watch for any distress and keep your roses cloaked in protection from a reliable pesticide/insecticidal soap.
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