Yellowing of boxwood leaves caused by Boxwood Leafminer feeding. Photo credit: Miri Talabac
Q: I have a low hedge of boxwoods that are looking somewhat orange-tinted and less dense than usual. What might be causing this?
A: Boxwood Leafminer is my primary suspect, and I have recently seen boxwoods looking just like you describe, which had high populations of this common insect pest.
With only one generation per year, this species of fly is currently in its larval (juvenile) stage inside the leaves. Since larvae feed on tissues between the upper and lower leaf layers, you need to peel the leaf apart to find them to confirm their presence. Outwardly, affected leaves will become blistered-looking and have a blotchy yellow or orange-yellow color. Leafminer damage can also cause the shrubs to shed some leaves prematurely, so the branches will have more sparse growth towards the plant’s interior than a healthy shrub would have.
Boxwood Leafminer larvae are tiny orange-yellow legless maggots, only a few millimeters long. However, they are readily visible if you open a leaf and examine it with a hand lens, since the rest of the leaf interior will be light green. They will pause feeding as winter approaches and overwinter in a state of suspended development, resuming more voracious feeding in early spring. Larvae pupate and transform into orange gnat-like adults by late April or early May (depending on temperature trends).
Boxwood leaf tissue has been cut away to reveal Boxwood Leafminer larvae feeding between the upper and lower leaf surfaces. Photo credit: John Davidson, Ph.D., UMD
Some boxwood cultivars have greater resistance to leafminer (as well as to fungal diseases) than others. When the insects are too abundant for their damage to be tolerable, prune out the infested branch tips or, as a last resort, consider using an insecticide to reduce their numbers. Keep in mind, though, that insecticide use can have unintended consequences: it might facilitate an increase in boxwood spider mites (by killing mite predators); harm pollinators visiting the boxwood’s flowers; or harm insect or spider predators wandering its foliage that would be eating pests.
You can learn more about leafminer as well as other common boxwood ailments on Extension’s boxwood diagnostic web page (go.umd.edu/boxwood]).
By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. 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. Our horticulturists are available to answer your questions online, year-round.
You may have suddenly noticed yellow nutsedge (Cyperus esculentus) crowding into your mulched garden beds or lawn in late summer/early fall. Also known as “chufa sedge, tiger nut, or earth almond,” this charismatic and fascinating plant was one of humanity’s earliest cultivated plants. It is still cultivated and considered a culinary treat in North and West Africa, western Europe, and China for its nutritious nut-like tubers attached to underground stems known as “rhizomes.”
Yellow Nutsedge (Cyperus esculentus) can quickly colonize bare spots in a mulched planting bed. Photo credit: Stacy Small-Lorenz | UMD
Yellow nutsedge can be identified by its yellowish coloration, stiff triangular stem, and three long leaf bracts at the base of a puffy brown flower. It tends to thrive in sunny areas with moist, disturbed soils. While similar in appearance to straw-colored flatsedge (Cyperus strigosus), it can be distinguished by its small, nut-like tubers. One yellow nutsedge plant can produce thousands of tubers, which allows it to produce more vegetation in the spring. Yellow nutsedge flowers in late summer and early fall and is a wind-pollinated plant that cannot self-pollinate.
Yellow Nutsedge (Cyperus esculentus) tubers and rhizomes. Tubers distinguish it from Straw-colored Flatsedge (Cyperus strigosus). Photo credit: Stacy Small-Lorenz | UMD
Yellow nutsedge colonized North America before Europeans did, so it is considered native here by some sources. In Maryland, it is most abundant in the Piedmont and Coastal Plain ecoregions. It is often treated as an aggressive agricultural and lawn weed across the U.S. because it can quickly take over disturbed areas and may outcompete lawn or garden plants. It tends to thrive in mulched beds and lawns that are overwatered or mowed too short.
To remove yellow nutsedge manually, you’ll have more success starting early in the season, when the plants have fewer than five small leaves. If you’re pulling in late summer or early fall, once flowers have developed, you might leave tubers and rhizomes behind in the soil that will only multiply. So, if you’re trying to manage its spread, try to remove as much of the underground plant material as possible, then stay on top of pulling it early when it emerges again next summer. You might also consider re-planting the area densely with a variety of native plants suited for sunny, moist conditions, then stay on top of weeding in spring.
If you choose to make peace with yellow nutsedge as part of your landscape, however, you can take comfort in knowing that its large underground biomass contributes organic matter and aeration to clay soils, improving water infiltration and soil structure for enhanced plant growth. It also makes a greater contribution to biodiversity than turfgrass – it’s a food source for Wild Turkeys and a wide variety of mammals that root up the tubers, and it is noted by the Maryland Biodiversity Project to be a larval host plant for the Dun Skipper (Euphyesvestris).
The Dun Skipper (Euphyesvestris) uses Yellow Nutsedge as its larval host plant. Photo Credit: Katie Woods | iNaturalist CC BY-NC
By Stacy Small-Lorenz, Ph.D., Residential Landscape Ecology Specialist, University of Maryland Extension.Read more posts by Stacy.
Scary plants earn Halloween points. Some plants are downright scary. Since Halloween is around the corner, I thought it might be fun to discuss a few.
Raise your hand if you love weeds. Okay, weeds are my nemesis. Yours too, I bet. If you’ve ever wrangled with mile-a-minute you’ve probably dreamed of this vine engulfing your house, your car, your dog. Ditto with bindweed, bermudagrass, and other brats. But armed with a little knowledge and persistence, you can get the upper hand. There’s a good weed ID guide on our website with photos and management tips.
Mile-a-minute weed spreads aggressively by seeds spread by birds. Photo credit: Leslie Mehrhoff, University of Connecticut; Bugwood.org
Much scarier are invasive plants. These plants are obnoxious spreaders that threaten ecosystems. English ivy, garlic mustard, and others bully out native plants that we – and wildlife – need. Lest you think I’m exaggerating, look at photos of garlic mustard blanketing forest floors or trees smothered in English ivy. These plants are a serious threat and need to be banished. Learn more at our invasive plants page.
Garlic mustard sneaking under a pine tree.An infestation of English ivy in a forest. Photo credit: Leslie Mehrhoff, University of Connecticut; Bugwood.org
Have you ever noticed a garden center plant labeled as “vigorous?” Beware. That could be nursery-speak for “spreads like wildfire.” These vigorous plants are often beautiful and can be tamed, but it’s best to go into any relationship informed. I call them my beautiful monsters, plants I can’t be without but need to manage carefully.
Mint will spread like mad so always, always contain it in a pot. Brazilian verbena (Verbena bonariensis) will drop seed like crazy. Deadhead it – or at least some of it – before it goes to seed. Obedient plant (Physostegia virginiana) is anything but obedient. Dig out its sneaky underground rhizomes where you don’t want it or enjoy it in others’ gardens. Yes, it’s a native, but it is a serious spreader. Forewarned is forearmed.
Obedient plant is anything but obedient, spreading quickly.
Another scary plant is poison ivy. I itch at the mention of its name. The merest brush of a leaf is enough to make me blister. First things first when tackling poison ivy. Cover any part of you that might come into contact with the plant. And consider having on hand a product that neutralizes the oils that cause itching. Remove small seedlings by hand. Sever vines growing up trees. Treat when you must, following the guidelines in our fact sheet. Ironically, we’re the only species for whom poison ivy is a problem. It’s a native plant with berries that form late to feed many forms of wildlife. It only irritates our skin and sensibilities.
Less scary are the plants in our gardens with a white latex sap such as milkweed, balloon flower (Platycodon grandifloras), and spurge (Euphorbia species). The sap can cause minor skin irritations, more of an annoyance than a threat. The same is true with juniper rash, the red dots you get from pruning junipers. Wear gloves to protect your hands from itchy spots and dots.
I hope I haven’t scared you too much. Most plants are quite harmless and a delight to both tend and behold. Into every garden a few itches, weed witches and vexing plants must grow.
By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. Read more by Annette.
Don’t feel guilty about being a little lazy this fall! Trying to remove every single leaf that lands in your yard is a lot of effort, without all of the reward.
Many municipalities will encourage leaf collection, sometimes distributing collection bags or vacuuming leaf piles from the street. The goal is to prevent leaves from making their way into our stormwater systems, where clogs could lead to flooding in the case of a large rain event. It is therefore important to follow local ordinances to relocate leaves in front and side yards that border a road. However, fallen leaves are valuable resources containing essential nutrients, and you may consider keeping some of this ruby and gold treasure for yourself!
Autumn leaves in reds, oranges, and yellows are beneficial as well as beautiful. Credit: Wikimedia Commons.
Here are some ideas for sustainably managing leaves in back yards and other areas where leaves are unlikely to be washed down a storm drain:
Move leaves onto garden and flower beds. You wouldn’t want to leave a thick mat of leaves on your lawn—it would kill the grass beneath; for that same reason, leaf cover is an excellent substitute anywhere you might put mulch. A layer of leaves (aim for at least two inches) will suppress weed growth in overwintering vegetable gardens, perennial flower beds, and around decorative shrubs. To stop the leaves from blowing away, wet them with a hose or watering can. These leaves will decompose slowly, releasing micronutrients back to the soil over time, retaining soil moisture, and helping your plants grow in the spring.
If you have more leaves than needed for your landscaping beds, simply mow over them where they fall. Mowing will break leaves down into smaller pieces, both preventing the thick cover that would smother your grass and speeding up the decomposition process. The additional organic matter will benefit your lawn.
Select a sheltered spot in your yard to leave fallen leaves intact. Insects need protection from the winter chill if they are to survive to the spring, and fallen leaves are excellent habitat! They insulate beneficial insects amidst the litter and in the soil below. Don’t mow the leaves in this sheltered spot, or you’ll shred the hibernating insects, too!
Ladybugs need warm, protected spots like leaf piles to survive the winter; as avid aphid-eaters, you’ll be glad to have them in your garden come summer. Credit: PickPik.
If you have a backyard composting system, fallen leaves are a great addition! The ideal compost mixture contains a combination of “greens” and “browns” (nitrogen-rich and carbon-rich materials, respectively). Dry leaves are considered “browns.” Crumbling them first will speed up the process.
Whatever options you choose, I highly recommend using rakes or at least electric mowers/leaf blowers over gasoline-powered yard tools, which are noisier and emit pollutants including carbon dioxide, methane, benzene, and other toxic and carcinogenic compounds that harm both human and environmental health. Now, I’ll ‘leaf’ you to it!
Manual yard tools like rakes are a more environmentally-friendly way to move leaves than gas-powered leaf blowers. Credit: Elenathewise, Getty Images.
By Sarah Rothman, Postdoctoral Fellow and Adjunct Faculty in the Department of Environmental Science and Technology at the University of Maryland. Read more by Sarah.
Q: Why are several perennials in my garden bed turning black? Can they all be affected by the same disease?
A: Most plant diseases are not that wide-ranging, but in this case, the black residue is not an infection. It is a fungal species, but this fungus does not cause plant disease, as it only grows on the surface. Named for its black color, sooty mold is a group of fungi that feeds on the sugars in honeydew. Honeydew is a waste secretion produced by sap-sucking insects, such as aphids, leafhoppers, soft scales, and planthoppers (which includes Spotted Lanternfly).
The numerous questions that UMD Extension receives each year about sooty mold often result from the presence of Crapemyrtle Bark Scale and Spotted Lanternfly. At this time of year, a heavy buildup of sooty mold from high populations of high-bark scale or lanternflies can be a prominent eyesore. Reduced rainfall that isn’t diluting or rinsing away the honeydew contributes to the problem, but it’s also due to increased insect feeding. (The juvenile lanternflies present earlier in the year don’t generate as much honeydew.)
Sooty mold wears off on its own over time. If the insects generating the honeydew are suppressed (which is not always necessary from a plant health standpoint), it deprives the sooty mold of its food source. If you want to try removing the residue, look for products with a horticultural oil active ingredient, which include specific directions for sooty mold treatment on the label. The spray may make the mold easier to dislodge several days later using a strong spray of plain water from a garden hose.
By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. 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. Our horticulturists are available to answer your questions online, year-round.
Q: Should I remove these fungi or are they beneficial to wildlife?
Fruiting body of a wood-decay fungus (Ganoderma) growing in a lawn.
A: This is a type of Ganoderma or a shelf fungus. They are wood decay fungi. You likely have some wood under the turf that they are feeding on. We do not recommend consuming them. If you don’t have any curious pets or children, you can leave them to fulfil their ecological role!
Q: Should I weed this plant or is it beneficial to wildlife?
American burnweed going to seed. The whitish-silvery hairs attached to the seeds help them disperse through the air.
A: Burnweed is a native summer annual in the aster family. It grows fast, produces abundant seeds, and can easily spread into garden beds and unmanaged areas of your yard. Various insects will eat this plant, and pollinators, especially wasps, visit the blooms, but it is not a critically important host plant for native insect species.
A lush American burnweed plant in early summer. Photo credit: J. Traunfeld
By Emily Porter, Horticulturist, University of Maryland Extension Home & Garden Information Center. Emily answers Ask Extension questions and helps manage HGIC’s Facebook and Instagram.
Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension. Our horticulturists are available to answer your questions online, year-round.
What do oaks (Quercus species), serviceberries (Amelanchier species), willows (Salix species), blueberry shrubs (Vaccinium species), ironweeds (Vernonia species), asters (many genera), and goldenrods (Solidago and Euthamia species); no, they do not cause seasonal allergies for most people) have in common? The National Wildlife Federation lists them as keystone plant groups of Eastern Temperate Forests, all native plants! Keystone plants provide a strong foundation for gardens— similar to how a keystone provides the final piece to an arch that helps distribute the weight evenly and allows the arch to hold.
“Native plant” is a term for vegetation that occurs naturally in a particular ecoregion. These plants have adapted and evolved to their native area, support diverse insect and wildlife species, and are key components of healthy ecosystems. Once established, they can thrive in Maryland’s climate with minimal maintenance.
Reasons to incorporate native plants into your landscape:
Beauty- flowers and foliage have interesting shapes, colors,and textures.
Soil Health- many native plants have deep root systems that help prevent erosion and do not require expensive and labor-intensive soil preparation.
Wildlife support- they provide important food sources for wildlife, including pollen, nectar, and insects that feed on them. Many specialist insects require specific plant species in order to feed or lay their eggs. A great example is Maryland’s state butterfly- the Baltimore Checkerspot- and its host plant white turtlehead (Chelone glabra). Prioritize keystone plants to build a strong foundation to support biodiversity in your landscape.
Lower maintenance- if properly planned, planted, and maintained, native plants require fewer inputs and attention. Occasional watering might be needed (regular watering during establishment is essential).
A longhorn bee (considered a specialist) on New York ironweed. Photo Credit: Boyer & McDowell
The “right plant in the right place” approach is equally important for native and non-native plants. In order for plants to thrive with the least amount of human help, we need to match their growing needs with the right location in our landscape, and when possible, the same ecoregion and habitat. Match the plants’ overall height with your goals for your site to save time and energy on pruning.
You can find your plant’s preferred growing conditions on the plant care tag or the back of the seed packet as well as in the resources at the end of the article. Match your growing location information to the plant care tag information below for successful plant establishment.
The USDA Cold Hardiness zone map ( planthardiness.ars.usda.gov) provides useful guidance. Enter zip code to figure out what zone you live in.
Match the available sunlight for your landscape with plant needs.
Full sun is 6+ hours of direct sunlight– but that doesn’t have to be continuous sun all day. It can be 3 hours of morning sun and 3 hours of afternoon sun for a total of at least 6 hours.
Part sun is 4-6 hours of direct sun.
Part shade is 2-4 hours of sun.
Shade is less than 2 hours of sun.
Natural soil moisture levels will influence how well a plant can grow. Site management strategies, like diverting storm water, can change soil dryness or wetness.
Native plants are not “pest-resistant.” They have evolved with local insects and wildlife. Birds, foxes, caterpillars, butterflies, and other insects feed on natives, so expect and celebrate these relationships. Many native plants will need protection from deer after planting until they are well-established.
Allegheny Serviceberry (Amelanchier laevis), one of the earliest spring-flowering trees. Photo credit: Boyer & McDowell
Guidelines for purchasing native:
Always look for the scientific name, genus, and species, not just the common name. For example, “sunflower” is a general name that could refer to many different plants– Mexican sunflower, pale-leaved sunflower, woodland sunflower, and many more. It is better to use the scientific name, Helianthus annuus, to avoid confusion.
Buy from your local ecoregion when possible; locally grown is even better! An ecoregion is an area with similar ecosystems— flora, fauna, climate, soil, geology, and land use history. For example, Garrett County is in the Mountain Region of MD.
Cultivars are generally not recommended— get the straight species for best ecosystem value. However, a native cultivar is better than a non-native, invasive plant species. More information about cultivars can be found on the Cultivars of Native Plant webpage.
Homeowners can help play a critical role in creating connections of native plant populations for wildlife corridors and conservation areas — every plant helps with the mission to restore and increase biodiversity.
What can homeowners do to help?
Remember the shoulder seasons— provide pollen and nectar sources for early spring and late fall in your landscape.
Add native evergreens to help offset the months when so many deciduous trees and herbaceous plants are dormant.
