DEAR NEIL: Last year my crape myrtles as well as the plants beneath them had the black sooty mold on their leaves and stems. I suspect it was crape myrtle aphids or scale.
I’ve read in your latest book that dormant oil spray applied in winter can help with scale insects, and I’ve seen that you recommend a systemic insecticide applied in mid-May. I need some clarification. Help!
Dear Reader: Crape myrtle aphids have been with us for many years. They coat the plants’ leaves with honeydew exudate in late summer, and the sooty mold grows in that sugary substrate.
Aphids are pear-shaped and fairly easily recognized. They can be controlled with a contact insecticide applied when you first see signs of the honeydew dripping from the leaves and coating surfaces below.
By comparison, crape myrtle scale is a much more recent invader from China. The white scale insects will be on smaller twigs and stems. They, too, exude the honeydew, but it may start earlier in the summer.
Prevention is the key to control with them, and that involves application of the systemic insecticide Imidacloprid as a soil drench around each plant’s roots, with that treatment being made in mid-May. That drench will also help with aphids.
If you follow those guidelines hopefully you will not have to experience the sooty mold outbreak.
DEAR NEIL: Can you mention eight or 10 good plants for a butterfly garden? I know whole books have been written on the topic, so I don’t expect you to do that. But could you name some that are really well suited to Texas?
Dear Reader: Oh, there are so many. Ones that come to my mind just from having grown them include butterfly weed (asclepias), vitex, Salvia greggii, lantana, Pride of Barbados, pentas, Gregg’s mistflower and butterfly bush.
Don’t overlook their favored food sources, including milkweed (monarchs), passion vines (gulf fritillaries) and parsley (black swallowtail). Tersa sphinx moth caterpillars feed on pentas.
DEAR NEIL: We live in an area with extremely rocky soil. I read your comments about Nellie R. Stevens hollies for privacy, where you recommended using 20-gallon plants for quicker screening. Could those survive in very large containers such as galvanized water troughs?
Dear Reader: Yes. Growers produce them in large pots (up to 200-gallon containers). However, they have no resilience if they get too dry. They will turn an insipid olive-drab color, often without wilting, and when that happens, they are probably lost.
So you will need to provide regular watering at all times. You don’t dare miss a beat. Of course, you’ll have to provide perfect drainage out the bottom of the container at the same time. They can’t stand in water. Your goal is to hit the happy medium.
You might be better served by a native species of juniper that is already able to grow in the rock. Let a local independent retail garden center professional help you choose.
DEAR NEIL: What is the best herbicide to kill clover in a newly established bed of Asian jasmine? Obviously, we don’t want to harm the Asian jasmine.
Dear Reader: Your only option with clover is a broad-leafed weedkiller (one that contains 2,4-D), but those do not differentiate between the various broad-leafed plants, Asian jasmine included.
If I didn’t have too much clover, I’d invest in a dandelion digger (a.k.a. “asparagus knife”) to cut the clover without use of a herbicide. Otherwise, you might buy a foam rubber disposable paint brush. It would allow you to wipe over the specific weed without getting the weedkiller onto adjacent plants – no spraying involved.
Do this before any new growth of the jasmine begins. It does come with risk of damaging any jasmine leaves on which it dribbles.
DEAR NEIL: I have an ash tree that has been neglected. When I was cutting brush around it I found that there were new shoots coming up from its base as well as from 5 feet up the trunk. Should I leave those or remove them? Should I cut the old trunk down? I’m trying to make up for past neglect.
Dear Reader: Ash trees are increasingly subject to loss due to different species of borers. That may be what has happened already to the top growth of your tree.
You asked my opinion, and I’d replace it with some other species far less prone to serious insect and disease problems. But if you decide to try to save it, I would select the straightest trunk coming up from near the ground and let it become your new dominant trunk.
Still, it’s only going to be a matter of a few years until it, too, succumbs. Texas is now seeing entry of a new and ultimately serious pest, the emerald ash borer. It has killed the ash forests in the Northeast, and its population has moved into East Texas.
Here is a report from last summer that is likely to be updated as this growing season unfolds. https://citybugs.tamu.edu/2018/07/23/emerald-ash-borer-makes-a-move/
DEAR NEIL: I have a protected spot where I have a bottlebrush tree. I need to prune to shape it and reduce its size just a little. When should I do that?
Dear Reader: I would do so in the next couple of weeks before it starts to put out a lot of new growth for this year. Just a thought – if you find that you’re having to trim it year after year you might consider moving it to a more spacious location.