Maryland Grows

The Nativar Dilemma: The Case of My Purple Ninebark & The Leaf Beetle

Physocarpus opulifolius 'Diabolo'

Ninebark ‘Diabolo’. Photo by F.D. Richards. Source: Flickr Creative Commons

I thought I was doing the right thing. When I moved into my house 11 years ago, I found a purple barberry shrub (Berberis thunbergii) planted in the back yard by the previous owner. I thought right away, it had to go. I knew Japanese barberries, so commonly planted in landscapes, were escaping into natural woodland areas and creating dense thickets to the exclusion of native plants. These thickets have been shown to make suitable habitat for Blacklegged Ticks. I wanted no part in contributing to that situation, so I donned my work gloves and removed that prickly beast of a shrub.

In the barberry’s place, I planted a “native” purple-leaf ninebark, Physocarpus opulifolius ‘Diabolo’. It had deep burgundy foliage that made a nice replacement for the burgundy-toned barberry. And, I was selecting a Maryland native plant. I thought it was a perfect choice.

I sang praises about this ninebark for years when people asked me for native plant recommendations. It has great spring blooms, beautiful foliage color, and I never had to prune it. And native plants support native insects so I was doing a good thing to help wildlife. I was doing the right thing!

Or so I thought.

It was just this year that I learned from my colleague, native plants specialist Dr. Sara Tangren, that this particular cultivar of the native ninebark was actually detrimental to a specific native insect, the Ninebark Leaf Beetle. My heart just sunk when I heard this. I am first and foremost a plant enthusiast, but I also appreciate insects—the essential roles they play in our world as well as their often stunning beauty. And when I looked up the Ninebark Leaf Beetle, I discovered that it is indeed a beauty. And then my heart sunk even further. My purple ‘Diabolo’ ninebark, it turned out, was no good for this native beetle. The alteration in the leaf color – changing the green of the native species to the burgundy of the cultivar – makes it distasteful to the beetle.

Ninebark Beetle

Ninebark beetle. Photo: Pennsylvania Department of Conservation and Natural Resources – Forestry,

The effects of altered leaf color on plant-feeding insects was noted in a new study published in HortTechnology magazine last month. The authors (Baisden et al.) conducted experiments on several native woody plant cultivars compared to the straight natural species. They looked at whether six altered traits in the cultivated varieties – leaf color, variegation, fall color, growth habit, disease resistance, and fruit size – had any effect on insect feeding, development, and abundance.

In all three experiments they conducted, the researchers found that the cultivars with leaves that were altered from green to red, blue, or purple deterred insect feeding. Results were not consistent for the other cultivar traits they tested.

ninebark leaf variations

Ninebark cultivars, ‘Lady in Red’, ‘Dart’s Gold’, ‘Diabolo’. Photo: Leonora (Ellie) Enking, Flickr Creative Commons

There are a couple hypotheses as to how leaf color affects insect feeding. Most plant pigments are compounds that do not contribute to the growth of a plant. They may instead provide a defense mechanism. Anthocyanin pigments make a red coloration that may warn insects that the plant has defensive, distasteful chemicals – and they stay away.

The question of whether cultivars of native plants – nativars – have positive or negative effects on native wildlife is an active and ongoing area of research. Results in past studies have been mixed. (For more on this topic, see Mt. Cuba Center research).

Physocarpus opulifolius

The native species of ninebark, Physocarpus opulifolius, has green foliage. Photo: John Ruter, University of Georgia,

I know how appealing it is to choose plants with special characteristics – the colored foliage, bigger flowers, the more compact form or general appearance that suits my personal taste. But my choices may not, in some cases, be to the taste of other things in our environment and the things that depend on them for food. It is a dilemma. I do like specific non-native plants (I’ll never give up my dahlias), but I also adore the lilting songs of chickadees in the springtime. Many birds like Carolina chickadees need caterpillars to feed their young and many caterpillars can only feed on wild, native plants. See New Smithsonian Study Links Declines in Suburban Backyard Birds to Presence of Nonnative Plants. I should note that a different study (Craves) found that native birds, including chickadees, were able to find insect food on non-native, invasive Amur honeysuckles. (Which makes the issue even more confusing, right?)

“When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” – John Muir

For an ecologically minded gardener, it feels complicated to sort this all out and do the right thing. I felt disappointed that my ‘Diabolo’ ninebark was a missed opportunity to support a particular native insect, but, as Dr. Trangren explained to me, it becomes more of a problem when cultivated nativars cross-pollinate with the wild species and change the genetics of the native populations, making them less capable of supporting insects on a broader scale. For this reason, she recommends choosing cultivars that are sterile.

It was a lesson learned and one that makes me more thoughtful about my plant choices and their broader impacts.

By Christa K. Carignan, Maryland Certified Professional Horticulturist; Coordinator, University of Maryland Extension Home & Garden Information Center.


Craves, Julie A. 2017. Native birds exploit leaf-mining moth larvae using a new North American host, non-native Lonicera maackii. Écoscience, 24:3-4, 81-90.

Baisden, Emily C., Douglas W. Tallamy, Desirée L. Narango, and Eileen Boyle. 2018. Do cultivars of native plants support insect herbivores? HortTechnology 28(5) 596-606.

Narango, Desirée L., Douglas W. Tallamy, and Peter P. Marra. Desirée. 2018. Nonnative plants reduce population growth of an insectivorous bird. Proceedings of the National Academy of Sciences of the United States of America.

Learn more about native plants on the University of Maryland Extension Home & Garden Information Center website.

Seeds to Die For

In the 1900s, Nikolai Vavilov studied botany and agriculture. He researched ways to make crop plants more disease resistant, drought tolerant, and higher yield. Working on behalf of the Institute of Plant Industry in Leningrad, he and his staff traipsed through villages, jungles, and savannahs around the world, collecting seeds from crops and their wild relatives. They were after the genetic diversity needed to breed new crop varieties. There was an urgency to their work; as populations of heritage varieties and wild plants cross-pollinated with modern cultivars, precious genetic diversity was lost. Their hard-won collection constituted one of the world’s first seed banks.

Vavilov Institute

The Vavilov Institute is an active genebank in the city now known at St. Petersburg. You can visit them at Photo Credit: D.T.F. Endresen via flickr. March 2002

Siege of Leningrad

Photo Credit: The Siege of Leningrad. English: “In a street of Leningrad after German air raid”. Photographer Boris Kudoyarov, Jan. 1, 1942. Provided to Wikipedia by the Russian International News Agency.

During World War II, Hitler’s troops laid siege to Leningrad for two and a half years. Many citizens died as the result of air raids, artillery fire, and in the second winter, as many as 100,000 people died of starvation each month. The scientists of the seed bank secreted parts of the collection away and took shifts protecting the remainder. As food became scarce, they pledged to each other never to eat the seeds in the collection. The seed collection survived, but nine of the scientists starved to death, surrounded by envelopes of beans, corn, oats, wheat, and rye.

The effort to secure the DNA of the world’s flora in seed collections continues today. Here are the world’s largest seed banks and how they continue the struggle to save the DNA needed to protect the future of our crops and natural areas:

USDA National Center for Genetic Resources Preservation


USDA Agriculture Research Service genebank lead scientist talks with Secretary Tom Vilsack during his 2013 visit. Some of the current fruits being studied are displayed on the counter. Photo credit: Lance Cheung, USDA.

The USDA’s genebank in Colorado is one of the largest in the world. They use the term “genebanks” because they store pollen and other plant parts involved in growth and reproduction as well as seeds. They also conduct research to improve the effectiveness of gene storage methods. Their cold room contains seeds preserved in vacuum sealed envelopes, stored on shelves at -18C (0F). These seeds have a shelf life of 20 to 50 years. The cryogenic vault area stores seeds in tanks cooled with liquid nitrogen. These seeds are expected to remain viable for hundreds of years.

Millennium Seed Bank

Working in partnership with countries around the globe, the Kew Botanic Gardens in London operates this seed bank focused on the conservation of native plant species of the world. Their mission is to provide an insurance policy against the extinction of species. Their initial focus is on dryland species. Dryland habitats will become drier with climate change, pushing many of these species beyond their tolerance range. At the same time, many moderate sites will become drylands, and these species will be needed to revegetate those areas. As of June 2015, Kew had succeeded in acquiring 13% of the world’s vascular plant species.

Svalbard Global Seed Vault

Entrance to the Svalbard Global Seed Vault

Entrance to the Svalbard Global Seed Vault was built to withstand sea level rise and nuclear attack. Photo credit: Miksu via Wikipedia

Svalbard is a gift to all of us from the Norwegian people and the Bill and Melinda Gates Foundation. Buried deep in a mountain on an island in northern Norway, Svalbard’s mission is to serve as a backup storage facility for the world’s other seed vaults, protecting them from the ravages of war, storms, fire, and war. Seeds are from both the USDA and from the Vavilov Institute. The staff of the seed bank in Leningrad would have appreciated Svalbard’s mission.

By Sara Tangren, Ph. D., Sr. Agent Associate, Sustainable Horticulture and Native Plants, University of Maryland Extension, Home & Garden Information Center

Resources on Seed Saving from the University of Maryland Extension

Monthly Tips for November

Ornamental Plants

  • pansiesPansies are a good choice for fall and winter color in the garden. If you want to plant pansies you need to do it very soon to assure that their roots get established for winter. As a bonus, pansies often overwinter and provide early spring beauty.
  • Spring flowering bulbs can still be planted. For best results, place them in a sunny spot in well-drained soil amended with compost. Fertilize the planting area with a balanced fertilizer containing nitrogen, phosphorous, and potassium. Bulbs can be protected from animal pests by surrounding them with a wire mesh like chicken wire. If deer or other wildlife have ravaged your past bulb plantings, try planting bulbs that are rarely damaged by deer, such as allium, narcissus, fritillaria, hyacinth, and scilla.


  • fallgreens1.closeup.Orazi_.'08.ppt_This is a good time to incorporate organic matter into your garden beds. Composted animal manure (horse, cow, sheep, chicken) is excellent for improving garden soil. Keep garden beds covered with shredded leaves to minimize the risk of soil erosion and nutrient run-off. These can be tilled into the garden in spring or left in place as a mulch between rows of vegetables.
  • Cover crops should be planted before Oct. 15 but increased soil and air temperatures, due to global warming, may allow early November sowing of winter wheat or winter rye.
  • Spinach, lettuce, arugula, kale, and other cool-season crops should be protected from freezing with a cold frame, plastic sheeting, or floating row cover. Be sure to vent your cold frame or plastic cover on sunny days to prevent excessive heat build-up.



  • You may notice large, brown humpbacked crickets with long antennae that don’t chirp. These are camel or cave crickets (photo on right) and are attracted to damp, dark locations in the home, usually in the basement, the garage, or garden shed. Exclude them as you would other nuisance pests by sealing up openings around foundations, doors, and windows.
  • Stink bugsladybird beetlesboxelder bugshouse flieselm leaf beetles, and a few other critters may be observed in large numbers congregating inside your home. Cooler fall temperatures are driving them indoors. The ladybird beetles are actually beneficial insects that will not breed or survive for very long indoors. Simply vacuum or sweep up any unwelcome guests. The stinkbugs and the other invaders will do no harm indoors except to be a nuisance. Escort these invaders out of your home or vacuum them up, but resist the impulse to spray an insecticide. You can also prevent pests from coming into the house by caulking openings around window and door frames and not storing firewood inside the house.

More tips from the Home & Garden Information Center

The Home & Garden Information Center’s horticulturists are available year-round to answer your plant and pest questions. In addition to gardening questions, we cover houseplants, indoor pests, and more. Send your questions and photos to Ask an Expert!

Ambrosia Beetles Are Behind Those Tubes

ambrosia beetle frass tubes

Sawdust tubes pushed out by ambrosia beetles as they bore into a tree. Photo: E. Nibali

Q: These things like spaghetti pasta were sticking out of our tree that suddenly died. They crumbled when I touched them. Did they attack the tree and kill it?

A: These are sawdust tubes pushed out by ambrosia beetles as they bore into your tree. The tubes are rarely seen this time of year. However, because of abnormal rainfall, some trees are producing ethyl alcohol, a reaction to stress. Alcohol production signals ambrosia beetles to attack. The beetles introduce a fungus into the tree, which clogs up its xylem (the water and nutrient transport system). Since your tree is already dead, it’s hard to say exactly what killed it. Its roots may have rotted or drowned from standing water or saturated, poorly draining soil. The ambrosia beetles may have merely pushed it over the edge. The beetles are not necessarily a death sentence. When numbers are low and a tree is fairly healthy, a tree can recover.

Learn more about ambrosia beetles on the Home & Garden Information Center website.

By Ellen Nibali, Horticulturist, University of Maryland Extension Home & Garden Information Center. Ellen writes the Garden Q&A for The Baltimore Sun.

Have a plant or pest question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.

Multi-colored Asian Lady Beetles Are Also Known as Halloween Beetles

multi-colored Asian lady beetle

Multicolored Asian lady beetle adult. Photo: Jon Yuschock,

To keep in the spirit of Halloween, I wanted to talk about a beneficial insect with orange and black coloration. The first to come to mind is the multi-colored Asian lady beetle, Harmonia axyridis. Both the coloration and the timing (now) that they move into homes and other structures have also earned this beetle the name “Halloween beetle”.

The multi-colored Asian lady beetle is the most common lady beetle I observe in managed and natural ornamental environments. The multi-colored Asian lady beetle is native to eastern Asia and was brought to the U.S. in 1916 to control aphids in food crops. At first, they did not establish well. Around 1988, an established population was found in a natural habitat. Since then, they have adapted very well and are now found throughout the U.S.

Adults of are highly variable in color and spot pattern. Their body color ranges from a pale orange to bright red, both with and without spots, and if there are spots their number can vary. One diagnostic feature for all multicolored Asian lady beetles is a dark patch in the shape of an “M” just behind the head on the pronotum. The juvenile stages or larvae are mostly black but with two lateral orange stripes on the middle segments of their abdomen. These larvae resemble tiny, short-snouted alligators with long legs. The larvae take a week or two to develop and then transform into pupae. Within a few days, the adults will emerge from the pupal skin and resume their hunt for aphids or other prey items.

multi-colored Asian lady beetle larvae

Multi-colored Asian lady beetle larvae. Photo: Joseph Berger,

Multi-colored Asian lady beetle adults are generalist predators that have been reported to consume more than 250 aphids each day and the larvae may eat more than 1,500 during their development. Multi-colored Asian lady beetles also will consume scales, a diversity of beetles and caterpillars. They are also omnivorous and feed on nectar and pollen from plants. They are highly beneficial when it comes to reducing populations of aphids. If you don’t spray your roses (or other aphid infested plants) with pesticides, these predators really can do their job well and suppress a pest population.

Not all good beetles are good all the time. In the fall months, as the weather cools, hundreds to thousands of multi-colored Asian lady beetles begin moving indoors to hunker down for the winter. At this time, multicolored Asian lady beetles are referred to as nuisance pests. In addition to their high numbers in buildings, they also produce a defensive compound that has a bad odor which makes them a little nastier when disturbed indoors. The best method to control multi-colored Asian lady beetle as nuisance pests is to prevent them from getting in the first place. Anything that can seal openings in homes will help in their control.

By Paula Shrewsbury, Ph.D., Associate Professor and Extension Specialist, University of Maryland, Department of Entomology. This article was published originally in the University of Maryland TPM/IPM Weekly Report, October 5, 2018.

Naked Garden Soil Is Not Cool… Keep It Covered This Winter

Plant and animal existence depends on healthy, functioning soils but humans too often treat it like dirt. We can improve soil health in gardens and on farms by:

  1. limiting soil disturbance (tillage)
  2. planting a diversity of plant species
  3. keeping soil covered throughout the year

These practices reduce erosion and nutrient run-off, build organic matter, and increase carbon storage in soils which helps mitigate the effects of climate change.

Leaf Cover

A thick layer of leaves (preferably run over with a mulching mower) is a terrific winter cover for small vegetable and flower beds. Bags of leaves from you yard or from neighbors’ yards are plentiful this time of year and allow us to sustainably recycle nutrients.

Whole leaves protecting soil and garlic plants.

Whole leaves protecting soil and garlic plants.

Try a Living Cover This Fall

We’ve had a number of relatively warm falls in recent years and can expect a continuing lengthening of the growing season as a result of global warming. We are past the recommended best date for sowing winter cover crops in Maryland. However, if you live in Central or Southern Maryland or on the Eastern Shore I think you can risk sowing winter rye or winter wheat with a legume, either crimson clover or hairy vetch, through the end of October. The soil and air temperatures should remain sufficiently high for germination and root establishment. Read More

Pine Trees: Browning Foliage and Pine Cones – Featured Video

Moving into the fall season, you may see some of your pine trees turning partially brown.  This is generally a natural occurrence.

Learn more about pines and other trees in the fall/winter season at our FAQ page.