Ask a Question forum: Did I ruin my knockouts?

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zone 5 - northern Illinois
Jun 27, 2017 7:34 AM CST
So far this year my knockouts have had lots of problems - black spot, rust and fuller's weevils. They bloomed wonderfully in the spring, but once all the blooms died off they became terribly unhealthy. No signs of new growth and the canes were all spotted with black spot. I even started spraying them in April with a fungicide. Yesterday I treated them with Bayer 2 in 1 for the weevils, but this morning I broke down and pruned the heck out of them. Cutting almost all canes to the ground because they were covered with BS all the way down. Did I mess up by pruning so much off this late in the season(June)? They've become such a pain. I'm thinking if I ruined them forever it will be one less burden at this point.
Name: Elaine
Sarasota, Fl
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Jun 27, 2017 8:54 AM CST
Hi and welcome, Nina. Gosh it's unusual for Knockout roses to have that much problem with black spot. Did you have an unusually wet and rainy run of weather late in the spring?

Anyway, about all you can do now is put down a little fertilizer, be sure they're mulched over the root system and getting lots of water through the hot weather and walk away for a few weeks. Either they'll bounce back with nice new foliage and another round of flowers or . . . you get to replace them. (next spring, preferably)

The Bayer systemic you used should give them a measure of protection, but if you can manage to always water in the early morning, and see if you can keep the irrigation water off the leaves (water low down, soakers are great!) that will help.

"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill
zone 5 - northern Illinois
Jun 27, 2017 9:34 AM CST
Thanks for responding. Oddly enough the first 2-3 weeks of June were super dry. I'm thinking I didn't treat them well enough for BS last year and it came back with a vengeance. I've also read that fuller's weevils make them more susceptible to fungus and disease. Can't find a whole lot of info on those little monsters in order to confirm that though.
Name: Rita
North Shore, Long Island, NY
Zone 6B
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Jun 28, 2017 9:06 AM CST
I doubt the pruning would do any harm. Roses simply bounce back from pruning with new growth. But yes., I am surprised that your Knockouts are having so many problems. I think keep with the Bayer Systemic spray.

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