trees and shrubs

Crapemyrtle woes

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An infestation of Crapemyrtle Bark Scale on a crapemyrtle trunk. Sooty mold is darkening some of the outer bark layers. Photo: Jim Robbins, Univ. of Ark. CES, Bugwood.org

Q:  My crapemyrtle has white stuff on the bark that I’ve never noticed before, though the foliage looks unaffected, if a bit dull lately. I thought these plants were pretty pest-free, so what might this be?

A:  We’ve had a lot of inquiries about this lately. Your plant has Crapemyrtle Bark Scale (CMBS), a non-native insect pest that was discovered in Texas in 2004 and confirmed in Maryland in 2020. Incidentally, crapemyrtles also can host Crapemyrtle Aphid, and it’s possible for the two to be infesting a plant simultaneously; their impacts on the plant are similar.

While CMBS could potentially feed on other host plants, so far they seem to strongly prefer crapemyrtle. The aphid sticks to crapemyrtle. Both secrete honeydew, the sugar-water waste common to sap-feeding insects, which is dulling the leaf appearance and probably cultivating a bit of sooty mold.

Since mid-Atlantic gardeners have embraced crapemyrtle to such an extreme that it’s everywhere you look, that’s a big buffet enabling this pest proliferation. We really need to diversify our landscapes.

Scale insects lead relatively sedentary lives, generally only moving about to any notable degree as newborns, appropriately called crawlers. After roaming to find a feeding site, crawlers settle down and stay put, using their straw-like mouthparts to feed on plant juices. Layers of protective wax, in this case felt-like and white, cover their bodies as they mature. For our purposes, this also means they are harder to treat with contact-type insecticides like oils or soaps because that shell prevents the pesticide from reaching them. Crawlers, running around shell-less for that brief window of time, are the most vulnerable life stage any treatment should focus on.

The problem is, this pest is so new to our area that we are still collecting data on when those crawlers appear. Insect development is dependent on temperature, so while we can make predictions based on how CMBS behaves to our south, we’re still refining our knowledge for Maryland. Complicating matters is the likelihood of several generations per year, and they might overlap.

For such a tiny thing with limited mobility, you may wonder how it got there in the first place. Like plant mites, crawlers can blow around on the wind, and might also disperse by hitching a ride on other animals, like birds. CMBS arrived in our area the way many plant pests do – accidental introduction on plants with undetected infestations shipped-in from out of the area.

Management of an established scale population, usually booming by the time we notice them, takes time. Don’t expect one or two treatments to resolve the issue quickly, and you’ll probably need to employ the services of a certified pesticide applicator. Manually scrubbing scale off while not wounding bark is difficult and not highly effective, given the nooks and crannies they can wedge themselves into that you cannot reach.

Not only should certified applicators treat trees too high to reach, but they will have more effective equipment and the ability to apply chemicals the general public cannot due to the Maryland pollinator protection law. Overlapping the use of more than one type of pesticide may be needed, and re-treatment might occur for over a year. Dead scale won’t fall off right away, though treatments for scale will probably suppress aphids at the same time.

While we usually suggest trying other methods to suppress pests, once scale are numerous, there is little recourse than resorting to pesticide treatment. Certain species of lady beetle larvae will consume these scale and could knock-down their numbers somewhat, so avoiding contact-type pesticide use or enthusiastic scale-squishing attempts does at least spare them. Drastically cutting back a large crapemyrtle is not recommended since that can ruin its branching structure, though you could try it with dwarf shrubby varieties since otherwise-healthy plants should regrow over future seasons. With proper application timing to avoid impacts on scale predators and other insects (something well-trained pesticide applicators and pest scouts know how to do), treatments can be done with minimal risk to the biodiversity in your landscape. Or…just plant something different and rely on other plant species to provide summer color.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more by Miri.

Have a plant or insect question? University of Maryland Extension has answers! Send your questions and photos to Ask Extension.

Q&A: Why are lilac leaves brown and curling?

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Irregular brown spots and blotches appear on lilac leaves, followed by leaf curling and defoliation in late summer. Photo: UME Ask Extension

Q: My lilacs look like death-warmed-over this time of year. Do you know what’s wrong, and is there anything I can do at this point?

A: Lilacs are sadly not very well-suited to our mid-Atlantic conditions. We’re at the southern edge of their heat tolerance, so while they weren’t among the best flowering shrub choices to begin with, climate change is only going to worsen their prognosis. Several types of leaf-spotting fungi and bacteria, plus general heat stress (which also increases their vulnerability to borers), results in foliage that looks quite beat-up by late summer. Brown spots, crispy leaf edges, and bare stems from premature leaf drop are all typical. You can explore lilac ailments and their management on our lilac diagnostic page.

No fungicide will reverse these symptoms once they appear, and while they might work as a preventative if applied before bud-break (and re-applied repeatedly well into the summer), it’s simpler to just grow something else if a plant is going to be that much of a hassle. This is especially true if the treatments don’t work and the plant still winds up looking horrible. Fungicides also carry the risk of harming other organisms.

For now, you can rake up and dispose of any fallen leaves, though this isn’t a foolproof way of removing a source of infectious spores. Cut down the oldest, thickest stems this winter (they tend not to bloom well at that age anyway) and open up the canopy by selectively removing some stems that contribute to foliage crowding. You can do this thinning after bloom next spring.

For anyone really wanting to grow lilac despite these challenges, try cultivars with above-average disease resistance and heat tolerance. While not immune to problems, they perform much better, even if they don’t look exactly the same or have blooms as large or heavily perfumed. ‘Miss Kim’ is a round, compact-growing cultivar with pale lavender-purple flowers that’s been around for decades. Other varieties are now available with pink or deeper purple blooms, some of which even rebloom a bit, sporadically producing flowers into summer and early autumn, though high heat could still hamper that.

dwarf lilac with lavender flowers
Dwarf lilac species and hybrids handle Maryland conditions much better than the traditional varieties. Some recent introductions will also re-bloom sporadically later in the summer. Photo: M. Talabac

All lilacs, but especially the traditional, classic “French” types, should be planted in a location with great air circulation (so, not up against a fence or wall) so wet leaves dry quickly after rain, dew, or irrigation. Wet foliage is more easily infected by pathogens.

The main perk of growing lilacs is fragrance, so if you want a scented replacement, consider: Winterhazel (Corylopsis), Koreanspice Viburnum (Viburnum carlesii) and its hybrids, Summersweet (Clethra), Seven-son Flower (Heptacodium), Carolina Allspice (Calycanthus), various deciduous Azaleas (Rhododendron viscosum and several others), Mockorange (Philadelphus), and Fragrant Abelia (Abelia mosanensis). Their scent characteristics, flower colors, mature sizes, and preferred growing conditions may differ from lilac, but nothing is going to be an exact substitute. Plus, several of these species will offer the additional bonus of showy autumn foliage or (for the native ones) better wildlife value. These are just some shrub ideas; there are also fragrant perennials and, if you have the room, several fragrant trees.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more posts by Miri.

Have a plant or insect question? University of Maryland Extension has answers! Send your questions and photos to Ask Extension.

How to adapt your garden to climate change

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The news is filled with references to global warming and climate change. In fact, 99% of scientists agree that climate change is real with negative impacts on the environment, weather, human health, and agriculture. In Maryland, climate change is already causing higher average temperatures, more drought, longer heat waves, more intense storms, and flooding. 

So what can we do as gardeners to help the cause and help our gardens adapt to these changes?

Adopt sustainable practices. Environmentally smart practices build climate-resilient gardens and can slow future warming by reducing emissions and boosting carbon in soil and plants. Here are a few ways to get started:

Plant more trees

Trees filter air and water and are carbon sinks, capturing and storing carbon dioxide, a key greenhouse gas. When placed well, trees can save up to 30 percent on heating and cooling costs.  

  • Plant deciduous trees on the west, east or southwest side of your home to block summer sun then let it in to warm your home in winter. Site evergreens to the northwest to buffer winter winds. 
  • Lean toward native trees. They’re well-adapted and need less water and fertilizer, the manufacture of which can contribute to greenhouse gases.  

Add or nurture native plants

Native plants such as this chokeberry and golden ragwort support wildlife and build climate resilience.
Native plants such as these purple coneflowers are pest- and disease-resistant and help build climate resilience.

Don’t stop with trees. Native shrubs, perennials, grasses, and groundcovers also help build a climate-resilient landscape. Native plants, once established, require less water and fertilizer, help store carbon, and reduce soil erosion. Since they co-evolved, native plants best support native pollinators and beneficial insects which provide chemical-free pest control. 

HGIC Website: Native Plants and Climate Change

Keep it diverse

Plant diversity also boosts resistance to pests and disease, so add many different types of plants to your gardens. Yes, more is better. 

Save the soil

Washington County Master Gardener Gary Stallings turns compost, a tool in building soil health and climate resilience

Great gardens grow from the ground up. So protect and improve your soil which stores massive amounts of carbon as carbon dioxide and organic matter.  

  • Keep soil covered since bare soil invites problems. Soil covered with plants, mulch, or cover crops best stores carbon, resists erosion, holds moisture, and has more even temperatures. 
  • Minimize soil disturbance from digging and tilling which speeds up the loss of organic matter and disturbs the soil community.  
  • Recycle nutrients by making and using compost. Compost adds organic matter, helps soil hold water and nutrients, and reduces the need for fertilizers. 

HGIC Website: Improve Soil Health for a Climate-Resilient Garden

Water wisely

  • Save water to make your garden more climate-resilient. Use a rain barrel or create a rain garden to capture and filter rainwater.  
  • Water when plants need it, not on a fixed schedule. And plant in the spring or fall when plants need less water to become established.

A few more tips:

  • Limit the emissions that contribute to greenhouse gases. Use gas-powered mowers, trimmers, and other equipment less and opt for alternatives. 
  • Shrink your lawn and replace it with groundcovers and other alternatives which need less water, mowing, herbicides, and fertilizer. When you do fertilize, do it based on a soil test to use only what you need. 
  • Help more by growing some of your own food or supporting local growers to cut down on emissions from long-distance transportation. 

You can make your garden more climate-resilient. Start with a few steps and build on them to help your garden successfully adapt to climate change.   

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.

This article was previously published by Herald-Mail Media.

Q&A: What is a good summer-blooming plant that’s deer resistant?

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Yellow flowers of St. Johnswort plant
St. Johnswort flowers. Photo: M. Talabac

Q:  What can I use as a summer-blooming shrub, especially if this part of the garden is sunny and somewhat dry? I also sometimes have deer problems.

A:  I think St. Johnsworts (Hypericum) are underused, and several species are native here in Maryland, though those might be harder to source. Some of the commonly-grown forms are non-native hybrids, though well-behaved ecologically. (The only locally invasive species, Hypericum perforatum, is fortunately not likely to be sold at a nursery.)

St. Johnsworts bloom anywhere between June and September, prefer direct sun, generally tolerate drought well, and are distasteful to deer. Blooms are nearly always an intense yellow, and some species or cultivars have colorful summer or autumn foliage. A few cultivars have berry-like seeds that ripen by fall and make good bouquet accents. I love the bark on native Hypericum densiflorum – peeling with a smooth underlayer that’s a rich, warm-toned cinnamon-brown that’s especially showy during dormancy.

You’ll find St. Johnsworts sold as both perennials and shrubs, because some species stay low, sprawl like a groundcover, and have stems that aren’t very woody, occasionally dying back in winter as other perennials do. Other species have woody stems and grow to about three or four feet tall and wide. Flowers are loaded with pollen, but no nectar, so butterflies will probably detour while bees and flower flies (predators we like to keep in the garden) will visit. Don’t deadhead developing seed capsules if you want to support Gray Hairstreak butterfly caterpillars, which can use Hypericum as a host plant (among a huge variety of other plants).

For more plant ideas, visit the Home & Garden Information Center’s pages on Plant Selection and Deer-Resistant Native Plants.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more by Miri.

Questions about home gardening? Send them to Ask Extension

Manage bagworms now so they don’t harm trees

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“Why are the pinecones on my tree moving?” a client asks.
“Because those aren’t pinecones, they’re bagworms,” I reply.  

Dangling from evergreens like teardrop-shaped Christmas tree ornaments, bagworms cause many a homeowner to scratch their head in wonder. Pinecones that dance?

Bagworms dangle from a juniper branch.
Credit: Erik Rebek, Bugwood

But the tell-tale thinning of trees that can follow is no laughing matter. Covered with bits of needles and leaves, the bags that give bagworms their name serve as protection for the caterpillars inside. Bagworm caterpillars are the juvenile form of a moth.  

That sounds innocent enough, but like all caterpillar-like insects, they are born hungry. Walking stomachs, they prowl among your trees, munching away to cause sometimes serious defoliation. They particularly enjoy evergreens such as arborvitae, cedars, junipers, and pines. But they will also dine on maples, locusts, lindens, and other deciduous trees.  

Eggs hatch out from bagworms’ bags in May. Tiny larvae spin an eighth-inch bag with bits of needles or leaves glued together with webbing. Like tiny backpackers, bagworms tote those bags around as they feed. As they grow, the bags get bigger and bigger and your tree foliage gets thinner and thinner.  

I don’t know if bagworms have an adventuresome streak, but they do a bit of hang-gliding. They spin a fine web and use the wind to glide to other trees in a stunt called “ballooning.” 

By August or September, the bags – and bagworms – are 1- to 2-inches long.  They stop wandering and feeding and tie up to a twig using tough silky threads. In late summer, they transform into moths. But get this, ladies, only the males have wings.  So the gals just hang out in their bags and wait for the boys to, um, visit. Post rendezvous, each female bagworm lays 200 to 1,000 eggs in its bag. Next spring, the eggs hatch to start the cycle over again.

Stopping that cycle is important and now is a crucial time. Mid-June to mid-July is the best time to treat trees with bagworms with a very effective organic control called Bt. A naturally occurring soil bacteria, Bt or Bacillus thuringiensis kills only small caterpillars. And guess what? Bagworms are just the right size right now.  Bt doesn’t harm humans or animals and is easy to find. It’s sold in hardware stores and garden centers under names like Dipel and Thuricide. Applying Bt is a do-it-yourself job if you can reach your trees with a sprayer. If not, call in a pro.

Even easier is picking off the bags if you have only a few bagworms. Snip them off with scissors or pruners, bag and trash them. Don’t leave them on the ground where the eggs can hatch. Since there can be as many as 1,000 eggs in each bag, removal is important. Get those bags gone. And gone before the eggs hatch in May.  

Tiny bagworms are hard to spot when they first appear in May on plants such as this Colorado blue spruce.
Credit:  Dave Lantz

Learn more about bagworms and see some great photos on the HGIC website.

You can beat bagworms and keep your trees safe. Fortunately, this is one insect for which there is an easy – and organic – fix.  So get out there and bag some bagworms.

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.

This article was previously published by Herald-Mail Media.

Q&A: Some insects have a lot of gall

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Maple Eyespot Gall, caused by a native midge (tiny fly) that occurs throughout the state. Photo: M. Talabac

Q: What on Earth is going on with this maple leaf? I saw it on a wild tree while taking a walk down a neighborhood path, but wonder if it’s something that can spread to nearby gardens.

A:  This is a great example of a gall, which is a tissue deformity on a plant caused by either insects, mites, fungi, bacteria, or nematodes. Usually galls cause swelling or weird projections on leaves or plant stems, but sometimes the more obvious feature is a color change like this.

The activities of the organism responsible creates chemical changes in the leaf tissue, redirecting tissue formation to suit its needs. For instance, insect-made galls give the larvae their own little house to feed in while being protected from most predators or harsh weather. (Impressively, tiny parasitoid wasps, little bigger than a dash on this page, still find their prey inside these structures and interrupt their life cycle. Isn’t that amazing?)

Despite how drastic galls may look to us, they don’t cause much harm to their host plants, which can be trees, shrubs, or perennials. Oak trees are renowned for harboring many kinds of eye-catching galls, some of which become most noticeable when they fall out of the canopy onto our lawns or gardens. See if you can find anything living inside those swollen red or brown lumps or balloon-like pockets on leaves. A wise bird or other insect may have beaten you to it, though, or the culprit is long gone and already flew away as an adult before the plant jettisoned the injured leaf.

If an eyesore, you can clip off heaviest infestations of leaf galls on witchhazel (caused by insects), azaleas (fungus), oak saplings (usually insects), and any other easy-to-reach plant. Keep in mind that the unaffected portions of those leaves are still functioning to feed the plant, so don’t remove too much growth. Otherwise, I suggest you leave them alone and just marvel at the intricacies of the natural world. Gall-forming insects can feed songbirds and don’t risk the health of the plant. As with any organism, populations wax and wane over time and galls might be prevalent one year and nearly absent the next.

At the Home and Garden Information Center, we have several web pages with more information about galls, including Shade Tree Galls and Eyespot Galls on Trees.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more posts by Miri.

Have a plant or insect question? University of Maryland Extension has answers! Send your questions and photos to Ask Extension.

Q&A: Why do my hollies and other evergreens have brown and pale leaves?

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holly with leaves showing sections of brown and pale color
Winterburn symptoms on holly. Photo: David L. Clement, University of Maryland Extension

Q: Several of our evergreens (different kinds) have brown or pale, bleached-looking leaves. Do they have a disease already, and can anything be done? Is it preventable in the future?

A: Most likely it’s winterburn, especially since most infectious diseases won’t cause symptoms this early and seldom impact several unrelated plants to the same degree. Winterburn is an abiotic disorder or injury – abiotic translates to without (a-) life (biotic) – meaning the condition has a non-living cause. Abiotic plant disorders are environmental, and causes include wind, water, temperature, and soil pH. In comparison, biotic factors would include insects, mites, fungi, or bacteria.

No treatment is recommended because the damage has been done, but winterburn is rarely a serious threat to a plant’s long-term health. As new growth resumes, the plant will eventually shed the damaged leaves. If it’s too much of an eyesore, you can selectively trim away the worst of it this month. Causes for winterburn typically involve a combination of cold temperatures, wind, and exposure to sun. Any autumn pruning that results in tender regrowth is priming a plant for winterburn, which is one reason it’s not recommended.

Why are cold-hardy evergreens damaged? Leaves “breathe” through tiny pores on their surface, and this gas exchange also allows water vapor to leave the leaf. Moisture leaves our bodies the same way – picture foggy breath on a cold day. Breezy days, especially in winter’s drier air, speeds-up this evaporation, as can the sun’s weak warmth. Meanwhile, during cold snaps, moisture in the surface layers of soil freezes, which prevents roots from absorbing it. Since the plant cannot replenish all of the moisture it’s losing, the leaf tissue starts to essentially freeze-dry. A thaw won’t reverse the damage because the cells have been injured, just like skin with frostbite. (Unlike our skin though, which can heal to an extent, leaf tissue can’t repair itself.)

Broadleaf evergreens are more vulnerable to winterburn than needled evergreens because the leaf surface area and evaporation potential is so much greater. Younger plants also have greater vulnerability because they are still establishing roots. This is the main reason it’s risky to plant evergreens late in the fall. Cherry laurel, boxwood, holly, rhododendron, camellia, and southern and sweetbay magnolias are common winterburn victims in our area. Plants kept in containers are also susceptible because their roots dry faster and experience more drastic temperature swings than they would in the ground.

The only actions you can take to minimize winterburn risk is to site evergreens out of the brunt of winter winds and to periodically monitor their root zones for moisture, irrigating when dry during a warm spell. Plants overwintering in pots can be sheltered a bit near a wall or windbreak, but don’t bring them inside as the interruption of dormancy may detriment their health.

Learn more and see additional photos on the Home & Garden Information Center website: Winter Damage on Landscape Plants.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension.