A rust gall on juniper with spore “horns” just starting to emerge. As soon as it rains after this point, the “horns” turn gelatinous and bright orange. Photo: M. Talabac
Q: I heard rust fungus can infect junipers but they aren’t worth spraying to treat. Is there anything else I can do to reduce the fungal spread from them to my other trees?
A: If you see and can reach fungal galls on the branches, clip them off. Some rust fungi (though not all) create a gall on their juniper hosts. Plant galls are tumor-like in that they’re clusters of malformed tissue, often in response to a pest or (in this case) an infection. When the weather starts to be consistently mild in spring and we receive enough rainfall, the galls where the fungus is spending the winter will begin to exude their spores.
These rust spores blow on the wind or wind-driven rain to vulnerable host plants like various members of the rose family. In our gardens, this includes apples and pears, hawthorn, serviceberry, quince, and crabapple. Fungus spores are extremely tiny, so how will you know what to look for? If the gall is producing orange goo, you’re missing the window since spores are already being dispersed. Ideally, remove all visible galls before this point, while they’re still hard and dry. Now is an excellent time to inspect junipers on your property for galls. Trim them off with hand pruners and toss them in the trash (don’t compost).
This is not a foolproof method for eliminating the risk of rust infection on other plants this year, but it certainly could help reduce the disease pressure. Fortunately, infections like cedar-apple rust, while an aesthetic nuisance from time to time, generally don’t cause serious damage to all hosts, though they can be more serious for some, like apple.
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.
Wintercreeper euonymus (Euonymus fortunei) overrunning a woodland floor and climbing tree trunks. Photo: Ryan Armbrust, Kansas Forest Service, Bugwood.org.
Q: I realize English ivy is widespread in Maryland, but there are some evergreen vines clinging to trunks that look a bit different than typical ivy leaves. Are they native, or should they too be removed?
A: An evergreen climber I see covering tree trunks in parks which might be confused for English ivy at a distance is wintercreeper (sometimes written winter creeper; Euonymus fortunei). This non-native invasive acts like English ivy in that it’s a groundcover when no support to climb is present, and a clinging vine when trunks or walls are available.
Wintercreeper vine. Photo: Chris Evans, University of Illinois, Bugwood.orgWintercreeper flowers. Photo: James H. Miller, USDA Forest Service, Bugwood.orgWintercreeper fruits in December. Photo: James H. Miller, USDA Forest Service, Bugwood.org
This species also has negative impacts on the trees and our ecosystem and should be removed if growing on your own property. Parks manage invasives as best they can, but with limited resources, we can do our part by not cultivating the species likely to spread into them, even if we don’t live immediately next to parklands. Weed Warrior volunteer programs exist, such as in Montgomery County, if you wish to be trained in invasive plant ID and to help with their removal on public lands. While wintercreeper has been banned for sale by the Maryland Department of Agriculture since 2018 as a Tier 1 invasive plant, established plants in the region can still mature enough to produce fruit (berries) that wildlife then inadvertently spreads into natural areas. Long a popular landscaping groundcover due to those vibrantly green leaves (and the variegated forms for their color), I always recommend removal and replacement with alternatives, preferably a medley of native species instead.
As with English ivy, it’s safest for the tree to simply sever the climbing wintercreeper stems’ connection with the roots in the ground and let them slough off the trunk on their own as they dry out and disintegrate. Even though they attach via root-like structures, those aren’t functional roots and no moisture or nutrients are absorbed by them. Pull up, smother (deny them light), or spray any running stems covering the ground. As with any tenacious weed, eradicating an established patch of this species may take time and repeated efforts at removal before finally being successful. Be vigilant, because birds could always re-introduce it in a future year. (Invasive plants…the gift that keeps on giving.)
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.
Although a non-native example, this New Zealand Hair Sedge (Carex comans) illustrates the soft, flowing look multiple sedge species provide. Photo: M. Talabac
Q: I’m happy to try a lawn alternative for my shadier areas but I’d like it to look more like a lawn than a groundcover or mix of flowering plants. What kind of grasses work for that?
A: Not many true grasses will grow well if you have less than full sun, but several perennials that look like grasses can work nicely. My primary recommendation would be to try one or more species of sedge (Carex). I was excited to see the study results for sedges from Mt. Cuba released recently: “Carex for the Mid-Atlantic Region” that may be a useful reference.
Mt. Cuba Center is a public garden and research facility in Delaware which displays and studies native plants, and they perform periodic plant trials to evaluate species and cultivars for garden performance. Lately they have been including an assessment of pollinator appeal as well, though in this particular case that wouldn’t apply since sedges are not grown for pollinator draw. (Even though the caterpillars of several of our less-often-seen butterflies feed on sedges.)
Sedges are a species-diverse group and make for an excellent grass-like aesthetic in partial shade to full shade. Many form low soft-looking tuffets, though with time or dense planting can form a more-or-less uniform “lawn.” Still, don’t expose them to much foot traffic since nothing is quite as tolerant to that as turfgrass. Well over one hundred sedges are native in Maryland, and the Mt. Cuba study results include lists of those well-suited to more sun than shade, more shade than sun, and a tolerance to mowing (not that they require it by any means).
A few true native grass species tolerate some shade, but won’t give you a comparable look to a lawn since they grow much taller or have a different leaf color or texture (often wider, coarser leaves). Examples include river oats (Chasmanthium latifolium) and Eastern bottlebrush grass (Elymus hystrix), which still could make nice accents if you wanted spots with showier seed heads.
The non-native asparagus relative mondo grass (Ophiopogon), which has dark green grassy evergreen leaves and a slowly-spreading growth habit, has been successfully grown as a lawn look-alike under mature trees. I would not recommend using its cousin Liriope, the spreading form of which (Liriope spicata) can be too aggressive and is considered invasive. (Plus, it’s way over-planted.) Mondo grass thus far does not appear to be colonizing natural areas in or near Maryland.
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.
Brown marmorated stink bug, one of the little stinkers that try to get into the house in autumn. Photo: Kristie Graham, USDA ARS, Bugwood.org
Q: The bugs trying to spend the winter in my home aren’t a hazard, right? I’m going to try to seal up where they may be getting in, but there are already some that have managed to appear inside that would be hard to track down.
A: They don’t bite, aren’t attracted to indoor plants (though they might be drawn to grow lights, as they are to any light source), and are generally just a nuisance. If not easy to find, you can let them wander around until they expire, then dispose of them. Live bugs can be vacuumed or caught and released outside to meet their fate. Boxelder bugs, brown marmorated stink bugs, and multicolored Asian lady beetles are the trio of common culprits here in Maryland. Crickets, pillbugs, and millipedes come inside too, but at least they don’t fly.
Our homes must look like giant boulders to them, basking in the waning sunlight and retaining relative warmth, riddled with inviting crevices in which they can wait out the winter. Our abodes might be especially attractive since our groomed landscapes don’t have as many natural tree cavities, fallen logs, brush piles, or layers of leaf litter to tempt them instead.
If anyone is still puzzled by how they’re getting in, check your door and window weather-stripping for degradation or gaps, look for torn window screening, and inspect vent covers and conduit or pipe entry points on the exterior of the home. Seal any gaps and cracks that you can. If you use a window air conditioner, take it out for the season or plug up any access points around it.
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.
Carolina mantis adult female in early autumn. Notice how her wings don’t reach the end of her abdomen, as they would with our other local mantids. Photo: M. Talabac
Q: I’ve heard that not all of our praying mantis types are native. They’re all good for garden pest control though, right, or are some bad instead?
A: Maryland is currently home to five species of praying mantis, but only one is native, which is the Carolina mantis. The others are the European, Chinese, Narrow-winged, and Asian jumping mantids, with the latter being the most recent introduction. While non-native, the other mantids have more-or-less been integrated into our ecosystem for some time now, so they don’t necessarily need management or removal. Evidence of this includes the fact that insect-eating birds and other predators will readily consume them, and their eggs can also be parasitized by the tiny wasps that presumably evolved to have a relationship with our native mantis. In the grand scheme of things, other invasive species deserve more attention. Plus, at least they also eat various other non-native insect pests.
If you prefer to support native mantids found in your yard, make sure you’ve identified them correctly. Maryland Biodiversity Project has image galleries for each mantis species and provides a few ID tips for telling the difference between them, at least for adults and egg cases (called ootheca). Put “mantids” in the search box to see the species list.
Photo: Pawel Pieluszynski
Mantids are generalist predators, so can consume pest insects and beneficials like pollinators alike. They’re opportunists, nabbing anything they can subdue (including each other), so are neither universally good nor bad. Gardeners generally consider them helpers since they do consume pests, though we don’t know to what extent the non-native species may be depriving the native species of a food source due to competition. (Given how many other non-native insects exist in our area, I imagine this impact isn’t that significant, especially when compared to the greater problem of habitat loss and degradation.)
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.
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.
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 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.
