kfelton0002
Full Member
Posts: 18
Joined: Sat May 09, 2015 7:28 pm
Location: KY Zone 6b

Blackspot on DBL Knockouts

My husband bought me two new 3 gallon double knockout rose bushes last month. I didn't really notice it until a month after I had them planted (I'm new to gardening) but they were completely infested with black spot, all the way down to the very bottom of the canes. They had brown spots on the leaves when my husband brought them home but I didn't know what blackspot was until I recently read about it. I did not want to take any chances with them possibly infecting my other roses so I immediately cut out all diseased foliage and cut the canes down to around 2 inches from the soil. I sprayed what was left with antifungal and medicated with Bayer Advanced 3 in 1. At this point since the plants were purchased without any kind of warranty (flea market type deal) my approach was heal them or kill them. With this treatment do the roses stand a chance of coming back without the infection and will they come back at all? Knockouts are supposedly really resistant to blackspot but it was not the case with these. I'm assuming they were kept in a really humid greenhouse environment because the new growth I saw after planting the roses had no blackspot, only the old growth. Thanks in advance for any input.

kfelton0002
Full Member
Posts: 18
Joined: Sat May 09, 2015 7:28 pm
Location: KY Zone 6b

Re: Blackspot on DBL Knockouts

They were in knockout containers and looked healthy other than brown spots on the leaves. I though at first maybe they had gotten too hot but then i researched blackspot and thats what it is. Knockouts are resistant to an extent but not immune. They can still get it if conditions are favorable for the fungus to grow. Or so Ive read. Thank u for the reply! I hope they come back.

imafan26
Mod
Posts: 11394
Joined: Tue Jan 01, 2013 1:32 pm
Location: hawaii, zone 12a 587 ft elev.

Re: Blackspot on DBL Knockouts

Roses with glossy leaves fare better against fungal diseases like powdery mildew and downy mildew, but when the weather is wet and humid the conditions are ideal for the fungi to grow.

Roses are high maintenance and for the most part require regular, pruning, feeding and fungicide and pest control.

Plant them near a street light, it deters rose beetles. Plant four o'clocks and/or garlic under them. That will also deter bugs.
Make sure the plants are well spaced and they get good air circulation and they are not planted up against solid objects like walls which will block air flow.

I use systemic rose care on my roses when the weather is hot humid and wet. It works well controlling blackspot, powdery and downy mildew and deters most sucking pests. It lasts for about 6 weeks. I disbud my roses when I am treating them since I want to minimize the harm to bees and other beneficial insects. When I look for roses, I try to buy ones that have glossy leaves and not the ones with matte leaves.

Baby blanket, a landscape rose, and red buttons, a rambler, are so resilient that not only do I not spray them, they grow like weeds. Hybrid teas are going to be the fussiest roses.

My winner tea roses are Peace, Queen Elizabeth, Iceberg, Mr. Lincoln, Chrysler Imperial, baby blanket, Neil Diamond, Scentimental, Proud land, Summer Fashion, Red masterpiece, Julia Child, Electron, and Chicago Peace. These have lasted the longest.

Simplicity also has survived since 1991 in my yard, and that is quite a feat. I am down to two from the eight that I had, but they pretty much are carefree roses.

Here are more suggestions for disease resistant roses.
https://extension.oregonstate.edu/garden ... tested-pnw
Happy gardening in Hawaii. Gardens are where people grow.

kfelton0002
Full Member
Posts: 18
Joined: Sat May 09, 2015 7:28 pm
Location: KY Zone 6b

Re: Blackspot on DBL Knockouts

Thanks so much for your knowledgable reply. I only hope to know so much about roses. I am just getting started growing them and actually taking care of them.

imafan26
Mod
Posts: 11394
Joined: Tue Jan 01, 2013 1:32 pm
Location: hawaii, zone 12a 587 ft elev.

Re: Blackspot on DBL Knockouts

It helps to join the rose society. You will get better help with learning to care for your roses and the members can help you choose the best roses for your area.

Knockout roses are supposed to be more disease resistant, but roses are roses, they won't be immune especially in hot, humid, wet conditions.
Happy gardening in Hawaii. Gardens are where people grow.

kfelton0002
Full Member
Posts: 18
Joined: Sat May 09, 2015 7:28 pm
Location: KY Zone 6b

Re: Blackspot on DBL Knockouts

I will look into that. Thanks! I dug up the worst one and put another knockout rose in its place. I put the one I dug up in a large pot until it starts looking better. I saw a little bud on it so it is still alive. Should I not have put another knockout in the place where I dug up the one with blackspot? I didn't really think about it until after I already had the other one planted. I treated with Bayer Advanced 3 in 1 Rose and Flower Care granules and I will spray it later this evening with fungicide as a precaution. Is this enough? I do not want my new knockout to become infected but the others are an eyesore and they are right in the front of my house. I am going to dig the other up as soon as I find a container large enough for it. Did I make a mistake in doing this? Jeeze gardening is so stressful. I thought it was supposed to be relaxing! lol

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