Rose heights, diseases shoot up this summer

Jody Jones’ Knock Out roses have shot up so tall in her Augusta yard that she’s going to have to have the neighbor boy come over to help her trim them down to size. She can’t see out of her bay window anymore.

“I have one cane that has shot up to 8 feet tall,” Jones said.

Earlier this spring, Betsy Latta saw, for the first time in her long rose-growing career, the trifecta of black spot, mildew and spider mites among the rosebushes. The fatal rose rosette – characterized by excessively thorny canes, distorted and frazzled foliage and strange red coloration – also has been spotted a lot around town.

It seems everything is up with roses this year.

“It’s like tropical. It’s like a jungle out there,” Latta said of the landscape. “Trees have grown, everything has grown with all the wonderful rain.”

But, Jones wonders, is the height of summer the time to go after the height of roses? She needs her view back.

“Right now is a good time,” Latta, who is a rosarian and member of the Wichita Rose Society, said. “If they’ve overstepped their bounds this year, you just have to whip them into shape.

“Whenever they’re between a bloom flush, just cut them back as far as you need to. You can shape them up. … Get the twiggy stuff down off the top.”

A couple of things to remember: Don’t remove more than 30 percent of a plant’s leaves at any one time. And don’t cut back after Aug. 1, because that will encourage growth that will be subject to winter kill, Latta said.

There are some other things to remember in the summer when it comes to roses. Fertilization can and should be done through Aug. 1, but don’t use a granular fertilizer after that, for the same reason you don’t prune after Aug. 1. But, “if you’re having a garden party in October, it wouldn’t hurt to put some Miracle-gro on the first of September to have blooms in October,” Latta said. In that case you’re using a liquid fertilize that isn’t as strong and will help with blooming rather than growing. It should not be used after Sept. 1.

“Fish emulsion is wonderful,” for that late fertilizer, Latta said. “It will give your roses a little boost without sending them out growing heavily.”

Latta recently saw some roses affected by rose rosette downwind of her yard in Riverside, and they were removed promptly. But “I have three roses that are looking suspicious,” she said.

Rose rosette, also called witches broom, is a virus carried by a mite that blows through the air, so removal and destruction of affected bushes is necessary to deter its spread. The virus always kills a rose, and there’s no treatment.

Black spot has been worse on roses this year because of the mild winter, extension agent Matthew McKernan said. Latta said that she sprays her roses through October, but black spot showed up last Nov. 1, and she didn’t do anything about it. Then this spring, “I had not only the few that had it in November but other plants. I had mildew and spider mites and black spot all at once. It was awful. The foliage looked terrible.”

Latta found that she had to use two chemicals: tebuconazole for the black spot, and propiconazole for the mildew. Strong blasts of water under leaves can dislodge spider mites.

This story was originally published June 30, 2016 at 8:22 PM with the headline "Rose heights, diseases shoot up this summer."