Rose Disease Hits Botanic Garden Roses
The echo barely dies down before the nursery professional turns to hear the question again. Here are the FAQs that are ringing through the air right about now. (I know it’s true, because I’m being asked the same questions as well.)
What can I do to treat the spots all over the leaves of my redtips and Indian hawthorns?
That’s a fungal disease called Entomosporium, and it’s a dead-end street for these two shrubs. I’ve written about it before here. First, it’s the freckles (spots). Then leaves lose their color. Then they turn brown and drop off, one branch at a time. Within a year or two the plant dies entirely. It may rebound a time or two, but it’s going downhill all the while. In spite of what some may tell you, there is no effective prevention or cure. Nellie R. Stevens or Needlepoint hollies are good replacements for redtips and Carissa hollies for Indian hawthorns.
What is causing the little beads of congealed moisture on the outsides of my peaches and plums?
That’s damage done by plum curculios. They’re the larval form of adult snout beetles that begin working on the young fruit soon after it forms. When you hear people referring to worms in their peaches, this is the pest. Your best means of preventing them is to spray Malathion when 75 percent of the petals have fallen. Do that spraying in the evening to avoid harming your bees. Pick fallen fruit off the ground in May and June and destroy it as well.
What are these warty little growths on my pecan leaves? What can I use to control them?
Those are pecan phylloxera galls, the result of insects that sting the young leaves as they are emerging and deposit their eggs in the leaf tissues. The pecan reacts by forming the gall tissues around the stings. The larvae develop within the galls until it’s time to emerge, fly and mate to start the process over again. Dormant oil spray applied in late winter is about the only treatment that will help. The good news is that phylloxera galls aren’t particularly harmful.
What are the little white bumps that are all over the stems of my crape myrtle? The stems are also black. What can I do to control both?
The white insects are crape myrtle bark scale, a comparatively new insect to the United States. It was first observed in Richardson, Texas, in 2004 and it has now spread across Texas and the South. As the scale insects feed on the sap of the twigs and stems of the crape myrtles, they secrete sticky honeydew that drips to coat stems, leaves and surfaces below. A black fungus called sooty mold grows on the honeydew substrate.
To control the mold you must control the honeydew, and to stop that you must kill the scales. Research at Texas A&M has shown that a systemic insecticide called Imidacloprid applied in mid-May gives the very best control by preventing major outbreaks for that season. It is applied as a soil drench around the base of the plant. For the record, Imidacloprid was once thought to be the cause of bee colony collapse, but current thinking among research scientists is leaning more toward a combination of many factors. Still early treatment with the soil drench instead of more general spraying should reduce the risk greatly.
Is rose rosette still a threat to our roses, or can I now replant roses into my garden?
The rose rosette virus is still active in Fort Worth and across much of Texas and America. In fact, someone visiting the Holy Land a few weeks ago posted a photo of RRV on roses in Israel to my Facebook page.
For those unfamiliar with this awful disease, it begins with very strong “bull” canes that skyrocket their way out of the rose bushes. They usually are marked by red stems and extraordinarily thorny growth. Buds on those stems fail to open properly, while other stems continue to function seemingly normally.
RRV is spread by a microscopic, wind-borne mite. There is, unfortunately no prevention or any control for the disease. There are those who will say that they have a cure containing hydrogen peroxide, but they are doing nothing to help the cause. All the while that folks are applying such home remedies the disease is spreading and killing others’ roses nearby.
My best advice at this point is to switch over to other types of plants as replacements. Or, if you decide to stick with roses and give them another chance, limit your numbers to what you can afford to lose after a year or two. Hopefully research currently underway will give us some hope in the near future.
Why is my St. Augustine not greening up uniformly? It has large areas of yellowed grass.
That’s a perfect description of take all root rot (TARR). It’s a soil-borne fungus that causes the grass roots to turn black and die off so that they do not function to take up nutrients even when you add them.
Dr. Phil Colbaugh, retired plant pathologist with the Texas Agricultural Experiment Station of Texas A&M, found that a 1-inch layer of sphagnum peat moss with its low pH would suppress TARR for one or two years. That has been a blessing for the past 20 years.
As I reported here six weeks ago, however, Dr. Colbaugh now suggests a fungicide called Azoxystrobin. He says that it stops the fungus rather than just suppressing it. In those six weeks I’ve been getting reports back from people who have used it and can already see positive results. It is sold under the consumer product name of Scott’s Disease-EX and the commercial applicator name of Heritage.