A great garden in a small space
I’ve covered each of them here before, but they keep coming up, and each is a serious concern. Here are four overwhelming issues gardeners are facing in North Texas landscaping, and you’ll want to scan through them.
Rose rosette virus
Anyone who loves roses has been heartbroken to see this disease move across the area the past 8 or 9 years. It’s actually a worldwide problem, but for some reason it has camped out locally, and it’s taken a terrible toll.
Symptoms of rose rosette virus include:
• Very strong “bull” canes;
• Extremenly thorny canes;
• Buds that don’t open properly;
• Red cast to stems and new growth;
• Weakened growth and death of plants within 10-18 months.
RRV is spread by a microscopic mite, and we have no chemical control for that mite. The virus gets into the vascular system of the rose plants, and once they’re infected, all we can do is dig, remove, bag and discard the afflicted plants. Because it’s a virus there is no chemical remedy. Those who tout hydrogen peroxide treatments are doing nothing to help – actually, quite the opposite. They’re leaving diseased plants in landscapes to infect others’ gardens.
What can you do? Destroy all diseased plants as soon as you identify RRV. I prefer to leave the soil idle for 1-2 years. If the disease is present in the neighborhood, I’m reluctant to replant roses. Dwarf crape myrtles are a suitable replacement. They bloom over a long period of time and grow to be about the same height. However, there are many other fine sources of color you might choose.
Crape myrtle bark scale
This insect was first observed in the U.S. in 2004 in Richardson, Texas. It is a pure white scale insect that adheres to the trunks and small twigs, often in fairly large numbers and occasionally in masses. 2007 was a horrific year for them, but most years since have not been so bad, perhaps due to different weather conditions or possibly due to an accumulation of predators. Bark scale gives off a sticky honeydew residue that serves as substrate for black sooty mold fungus. That’s actually what most people find most annoying.
At first the pest was confined to the Metroplex, notably to Dallas and eastward, but in more recent years it has spread much more widely across Texas and almost the entire Gulf South. A group of southern Land Grant (agricultural) universities have banded together to conduct research on the pest, so expect more information in the next few years.
I work with crape myrtles a good bit. Here are a few of my observations and things Texas A&M entomologists have taught me.
• The scale is more unappealing than damaging. It does weaken the plants, but it rarely kills a plant that was otherwise healthy before the attack.
• A particular species of ladybugs is known to feed on this scale. It is black with two orange-red spots on its wings, giving it the name of the “twice-stabbed” ladybug. Larvae of this ladybug are very different looking than the adults. People become alarmed when they see them. It’s difficult to convince them that they don’t need to worry.
• Based on recommendations of Dr. Mike Merchant, urban entomologist with the Texas AgriLife Extension, one can get a very satisfactory level of control of crape myrtle bark scale by (1) washing the trunks with a soft brush filled with soapy water and (2) applying a drench of Imidacloprid systemic insecticide according to label directions. That treatment should be made in the first half of May. His very thorough video explaining the treatment is at https://citybugs.tamu.edu/2018/08/28/how-to-treat-your-crapemyrtle-for-bark-scale/
Take all root rot of St. Augustine
This spring fungal disease causes the grass to be pale green or even yellow in “washes” across the lawn. On closer examination you find that the roots are shortened and black and that the grass pulls loose easily from the ground.
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 would suppress the spread of the fungus for a year or longer if applied at this time. And for years that was our recommendation.
This year, however, Dr. Colbaugh told me that the fungicide Azoxystrobin has given good results in actually stopping the spread of the fungus, not just slowing it, and at a far lower cost. You’ll find it sold under the consumer product name of Scott’s Disease-EX, or your commercial lawn care company may be using it as Heritage. If you are seeing TARR in your lawn, this is the time to treat.
Entomosporium on redtips, Indian hawthorns
This disease starts with harmless-looking maroon freckles. Within a few months the plants begin to lose much of their dark green color and isolated branches turn yellow or white and die out entirely.
The infections began with redtip photinias 30 or 35 years ago, and they have gradually spread to Indian hawthorns. The two species are closely related, and now neither of them should be planted in large numbers in landscapes. It’s not a matter of “if” they’ll succumb to the disease, but actually “when.”
Unfortunately, we have no chemical control yet for Entomosporium. But you can plant Nellie R. Stevens, Needlepoint or dwarf Burford hollies to replace the redtips (depending on the height of plant that you need) and Carissa hollies to replace the hawthorns. Of course, there are other options, but I’m a holly fanatic and I proudly admit it.