Diseases

July 21, 2018

I'm getting calls about the rose rosette virus and how to prevent it.  Several people think we need to ask garden centers and nurseries not to buy any more roses so it can't get here. I don't think that would work or will happen, but is there anything that I can share that will help.

Rose rosette has been a problem for years, but we had more issues with it last year than ever before. I think one of the main reasons is that more and more people are planting roses--in the form of the Knockout and other carefree roses.  Thus more disease issues, because more plants are out there.  One other thing I just learned this year is that the mite that spreads the rose rosette virus lives on the top of the rose bush overwinter.  Heavy pruning of the roses prior to new growth, and destroying the cuttings you take off, could help prevent the mite from surviving.  If you think back to last year, we didn't have a winter and many of our roses, especially Knock outs were blooming in February.  Many people didn't prune them at all, or very little. And then we had more rose rosette. In fact, our recommendation was that you did not ever need to prune Knockouts as severely as hybrid teas, saying a light shearing was fine. Now we are re-examining that, and recommending cutting all bush roses back to about ten inches or so in the dormant season--late February.  If you have the wild mulitflora rose in your area, trying to eradicate that can also go a long way in getting rid of the mites, which breed there as well.  Roses have traditionally had problems with diseases and insects.  Hybrid teas get black spot and they look ugly if you don't spray.  The new carefree roses gave us non-stop blooms with no spray schedules and people have flocked to plant them. Rose rosette is a virus that can attack all roses, and there is no cure once it gets it.  Breeders are working on rosette resistant varieties, but so far haven't found any, but with proper pruning and good sanitation--removing plants when they have it, can help in the long run. I don't think we will ever see gardens without roses in them, or at least I sure hope not.

October 14, 2017

I would like to know what can be done about black spots on yellow leaves of rose bushes.  My plant looks awful. 

Black spot on roses is a very common fungal disease on roses.  It starts out with black spots on healthy leaves and then the whole leaf will turn yellow and begin to shed.  Many hybrid tea roses are highly susceptible, while newer Earth Kind roses are more resistant.  If you have a variety that is susceptible, you don’t wait to get the disease, you start a fungicide spray program in the spring when they begin active growth and continue it throughout the growing season.

(October 2007)

My rose bush has black spots on the leaves and they turn yellow and fall off. I have sprayed it with disease spray from the gardening center but it hasn’t helped. Now it has almost no leaves and looks like it could die. It usually blooms a lot in the spring and summer, but this year it only bloomed in the spring and has been pitiful ever since. I have had it for about 10 years and don’t want to lose it. What can I do? Also there was an ant bed underneath it (small black ants and we sprayed them, could they have damaged the plant?

Your rose bush has the classic rose fungus disease called black spot. This was a great season for diseases of all types, but if you have a susceptible variety, you typically have the disease every year in Arkansas. Spraying after you see the disease is usually a futile attempt at control. The key is to start your spray schedule in advance of the disease—soon after the plant kicks into growth in the spring. Sprays every week to three weeks—depending on what product you use, will be necessary throughout the season. Black spot can weaken a rose bush, and if it occurs year after year, it can weaken it enough for it to die, but it should come back strong next spring with proper pruning, spraying and fertilization. I don’t think the ant spray had any effect.

(July 2006)

We have a brick mailbox with a rounded top. I have 3 climbing rose bushes that I want to climb over the top of the mailbox. I got busy last fall and did not prune them. We had a lot of roses this year, but there weren’t a lot of leaves. The roses have finished blooming and they are scarce as far as the leaves go. The leaves that are there look green with no spots. After they started blooming this year, I fed the bushes and also applied the Bayer liquid for roses. At this time, I have several limbs with little or no leaves that are going all over the place. There are a lot of thorns. Any suggestions of how to train these climbing roses to climb over the mailbox? Should I go ahead and prune them now? I was just not sure, because if I keep pruning them, they will never be long enough to climb the mailbox.

Climbing roses can bloom all summer or only once in the spring--it depends on the variety. Many people are uncertain as to when to prune so they just don't and the plants get gangly and less thrifty. Allow climbers to bloom in the spring and then do your pruning. Normally we like to take out one to three older canes and take out the thin, weak wood. Taking out an old cane now is not going to hurt but recovery will be slower since it is hot and dry. The goal is to have a variety of aged canes with foliage from the ground up. Mailmen are often not fond of a lot of landscaping around the mailbox, as bees can compete with mail delivery. Have some type of trellis for them to grow on, prune annually after the first flush of blooms in the spring, fertilize monthly, water as needed and control black spot when it is needed and your roses should do well.

(July 2007)

My running rose is losing all of its leaves. It bloomed very well earlier this year, but looks awful now. Can you tell me what the problem is? The plant is only about two years old.

The common fungal disease black spot, has defoliated many roses this growing season. This disease attacks a variety of roses, from bush types to climbers. The disease starts off with small black spots on the leaves, which over time yellow and fall off. If you grow a variety that is susceptible to the disease, the key is to spray in the spring after they begin growing with a fungicide such as Daconil, Funginex, Immunox or Bayer All in one Rose spray. Regular spray schedules are needed all season long following the label directions. At this point, starting a spray program would be futile. Trying to control a disease that has become firmly entrenched is fighting a losing battle. Prevention is key. For now, I would water when dry, lightly fertilize and hope for a better year next year.

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