Why are pecan trees and crape myrtles “raining” a sticky substance?
Many of our viewers have reported sticky lawns, sidewalks, and cars and are worried about their trees and shrubs. Well, although I can completely understand why you would be concerned, this “rain” is actually just a sugary substance, referred to as honeydew, that’s caused by insects feeding on the leaves and other tender parts of plants. On pecan trees, aphids are most likely to blame. And on crape myrtles, I’ve noticed that white flies are more commonly the culprits right now. These insects feed by injecting their proboscis into the phloem and feeding on the plant’s sap, which is pretty much pure sugar. So, when these insects excrete their waste products, that waste is also almost pure sugar. Sooty mold, a secondary pest, then moves in to take advantage of the situation. This fungus feeds on the excreted sugar, so you’ll probably also notice a black substance on your plant’s leaves. Sooty mold is actually a bigger issue than the honeydew, because it interferes with the plant’s ability to soak up sunlight.
We thank viewer Felicia for these pictures of her blotchy pecan tree leaves. Bill Ree, an Extension specialist that focuses on insect issues in pecans, told us this: “Managing the honeydew from aphids is a real challenge. On many occasions for the homeowner, I have recommended just a good hard spray of water to remove aphids and honeydew.” Bill notes that the ones on Felicia’s tree are the black-margined pecan aphid. They go through cycles, building up during June and July. Then we’ll get another, smaller invasion in August and September. But really, even getting all of the insects off with water is impossible on mature trees and shrubs. Unless they’re very young, pecan trees are too tall to reach all of the insects, and crape myrtles have small leaves and lots of nooks and crannies, so you simply can’t wash all of the insects off.
Your best option really is to do nothing, and simply let nature take its course. Ladybugs and green lacewings may take care of the problem by eating the aphids. And parasitic wasps will lay their eggs on the aphids to raise their young. But even if there are not enough beneficial insects around to control the damaging ones, pecans and crape myrtles are deciduous, so they’re going to drop those infested leaves this fall, and produce new leaves in the spring. And hopefully next year we won’t have as bad of an infestation. You can also help plants through the stress by watering them slowly and deeply, so that they may be able to produce a few more leaves and put on some new growth this season, before they go dormant. If you’re planting a pecan tree for the first time, consider a variety that has a tolerance to aphids, such as Pawnee, Kanza, Lakota, and Sioux.
Animals chewing tree bark?
Viewer Connie asked us what to do about her young elm that a porcupine chewed. Will young trees recover? Unfortunately, the answer is maybe yes, maybe no. It all depends on the extent of the damage. The growing tissue, called the cambium, of young trees, is located very close to the surface, so if the bark is damaged, the growing tissue most likely is too, and the plant cannot regrow this very important area. But if the damaged area is small, the tree will grow around it, and create other connections from the roots to the growing tissue above. Eventually, the damaged area will be covered by new bark and will be less susceptible to secondary infestations of insects and diseases. Younger trees recover faster than older trees. And many times, critters are more attracted to younger trees, whose bark is more tender and less thick, so quite often the tree is able to recover. If you notice any damage, or if you know that you have critters living in your area, protect the tree by enclosing it in a fence for a few years, until it gets old enough and has thick enough bark to be less attractive to animals. Once the bark is thicker, the tender growing area is much farther from the surface, so even if you have damage, maybe from a deer rubbing his antlers on the tree, the cambium won’t be damaged. You definitely don’t want to use plastic or other materials to wrap the tree; those will trap moisture next to the bark, creating a perfect environment for insects and diseases. Hardware cloth makes a very good fence. Place it around the tree, very close, so that critters can’t sneak in, but not directly touching the tree. Connie also asks if she should spray anything on the damaged area to protect it. No, that isn’t necessary. It won’t help keep animals away and will actually inhibit the plant’s natural ability to heal itself.
What’s wrong with my Mandevilla plant?
Viewer Marie’s plant is in a large pot, getting sun until about 2 in the afternoon. The leaves are yellowing and have some splotches, and some leaves are falling off. Well, Marie, there are definitely a few issues here that we can help with. First, the amount of sunlight. Mandevilla are tropical species, and although they do need more sunlight than many tropicals, they still can’t take the searing intensity of our sun here in Central Texas, and more importantly, they struggle in the moisture-sucking heat that comes with it. We have our Mandevilla in very bright shade in our demonstration garden, and they perform very well. Leaves grown in shade tend to be darker green, so give your plant a good shearing, to remove the yellowing leaves and struggling growth, after you’ve moved it to a shadier spot. Then watch for the new growth, which should be slightly darker. Some of the leaf damage here is sunburn, but most appears to be photooxidation. When sunlight is very intense, it can burn sensitive leaves, causing brown spots, or sunburn. But before the leaf completely burns, you may notice yellowing leaves, which is a sign that the heat of the sun has denatured the chlorophyll. And since chlorophyll is a green pigment, less chlorophyll means less green. The smaller brown splotches here are likely secondary issues, possibly fungal, which move in once the plant is stressed and vulnerable. So Marie, move those containers to where they won’t get direct sun any later than mid-morning, and shear the plant to about 6 inches to force it to produce new, healthier growth. You’ll see improvement in no time.
Why do jalapenos turn red?
Well, if you’re growing jalapenos for the first time, or you’ve never lost track of harvesting them and let them go too long, you may not have noticed that a natural development of these fruit is the reddening when they actually ripen. Normally we harvest them green, which stops their development, because they’re much more tender and tasty at this stage. But if left on the vine, they do indeed turn red and begin to dry out, the way any seed pod does. Because we’re usually interested in eating the flesh of the pepper, we don’t want it to dry out, so we harvest them green, while the flesh is still nice and juicy. And if allowed to ripen, that valuable flesh begins to dry-up and the flavor changes. You may see red-flesh jalapenos sold in the market, but more often you won’t: most red jalapenos are dried, smoked, and given a completely new name: chipotle. Chipotle peppers are used in cooking to provide a unique smoky flavor, and not the heat normally associated with jalapenos. So if your jalapenos are turning red before you can harvest them, that’s just a sign that you need to eat more jalapenos, or that you need to experiment with creating some chipotles. .
Butterfly or orchid vine, Mascagnia macroptera
It thrives in the heat and sun, but also does well in part-shade. It prefers well-drained soil and is very drought tolerant. It may go dormant in cold winters but will return in spring. It can be a bit invasive, but that depends on your point of view. It attracts bees and other beneficials, but is deer resistant. The seed pods resemble butterflies and can be dried for crafts and decorations. Here are a few beautiful designs crafted by young Nina and her friend Tylar. They even included poppy seed heads. Thanks to mom Maria for sharing!
Gray Santolina, Santolina chamaecyparissus
Fortunately, Santolina is most commonly referred to by its common name and is almost never confused with other plants, so you won’t need to learn how to spell or pronounce its mouthful of a Latin name. This lovely little evergreen, or ever-gray, groundcover is a cute little button of a plant that eventually spreads and covers the ground up to two feet wide. It usually stays short, only about 12 inches tall, but it may get as tall as 2 feet. It loves the heat and sun and prefers very well drained soil, requiring almost no water. In fact, like many desert-type plants, Santolina will suffer greatly if over-watered. The leaves are very fragrant, making it resistant to deer, and during summer it will produce a prolific amount of small, bright yellow flowers that will persist for a very long time, making them a great addition to dried floral arrangements.
Shoestring Acacia, Acacia stenophylla
This strikingly unique tree is widely used in the desert southwest, not only for its beautiful form and weeping habit, but also because it thrives in extreme heat with very little water once established. As with the majority of southwestern species, this tree will not take kindly to poorly drained soils, so if you have heavy clay, you might want to choose another species. Shoestring Acacia grows 20 to 40 feet tall and will have a canopy about 15 feet wide. From a distance, it resembles a willow tree, with very long, shoestring-like leaves. I could go off on an excited botanical tangent here, about how the “leaves” are actually modified structures called phyllodes, but I’ll spare you that plant-nerd ramble for the moment. Shoestring Acacia is a relatively fast-growing tree, with all of the potential issues that come with it. It has a rather thin trunk and long, thin branches, leaving it more susceptible to breakage and wind damage. This tree is evergreen, and is best used as an accent, to enhance the beauty of your landscape: with its diffuse leaves and billowy habit, it provides very little shade. Shoestring Acacia has a similar, powder-puff flower to other Acacias, but you may hardly notice them amongst the graceful foliage. Although this tree can be virtually ignored once established, when you do water it, be sure to do so deeply and thoroughly, but not too much or too often, or it might develop root-rot.
Lindheimer’s muhly, Muhlenbergia lindheimeri
This gorgeous ornamental grass is native only in the Edwards Plateau region of Central Texas, but has become widely used in the nursery trade. And for good reason: the sharp bluish-gray foliage and seed heads create a striking addition to any garden. These perennial ornamentals look especially at home in a xeriscape, planted with other low water-use plants like black foot and Copper Canyon daisies. The plant itself gets only 2 to 3 feet tall and wide, but once it’s in bloom, the flowers spikes can extend that another 2 to 3 feet. Since they fill in quite nicely all the way to the ground, Lindheimer’s muhly, also known as big muhly, creates a very nice screen when planted in a hedge row. Big muhly is native to dry prairies and rocky outcrops, but it can tolerate a little extra moisture if rainfall is high and your soil is a bit heavy. It easily thrives in the full, hot sun with very little water, so once established, you can virtually ignore this plant. The native species have lovely pale-gray inflorescences, which are called panicles in grasses. Improved varieties with pale yellow and even reddish panicles are also available. One of the most popular is ‘Regal Mist,’ with deep pinkish-red flower spikes that develop in the late summer and add color to the garden into early winter, when most plants are going dormant and their color is fading. The fine, uniquely colored foliage also adds textural interest to the garden, in addition to color. Place big muhly in conspicuous areas of the garden, near walkways or in borders, and allow it to shine as sculptural element, all year long.