Beautiful Native Plants

Blog HOME ***Our team of bloggers writes about various aspects of ecosystem gardening from native plants to pollinators and wildlife.***

Saturday, February 25, 2017

Viburnum Under Siege. Part Two

Editor’s note: this is part two of this series. Don’t miss part one of Viburnum Under Siege.

The accidentally introduced pest, viburnum leaf beetle (Pyrrhalta viburni) or VLB for short, can destroy a shrub in just a couple of years. Unfortunately it continues to spread through North America. So I am trying to learn more about it, hoping that we can protect the viburnums in our area. This is the information that I have gathered from the sites listed and from my own observations. It doesn’t look very encouraging.

VLB larvae and leaf damage
© Beatriz Moisset
The grubs or larvae emerge from eggs early in the spring. They are yellowish or greenish, with black markings and can reach one third or a quarter of an inch in length.
They spend a few weeks feeding on the leaves by making numerous little holes between the veins. These holes are easy to identify. By early or mid June they climb down along the stems and bury themselves in the ground to pupate. When I searched for them in mid June, I found none, only the damage remained.

By the end of June or in July, the adults emerge and start feeding on the same shrubs, making more holes that look similar to the ones made by the larvae. The adult beetles are about a quarter of an inch long, brown, with a golden fuzz coating the body.

VLB egg caps on terminal twig
© Beatriz Moisset
Females lay eggs on twigs, after chewing up a round hole. They cover a batch of about 8 eggs with a cap made of sawdust and their own feces. They can lay as many as seventy batches aligned in rows near the far end of a twig. The eggs spend the winter well protected against predators and the weather under this nasty mess. Their only serious threat to their survival is the crushing mechanism that many non-native viburnums possess.

Most native viburnums, such as arrowwood (V. dentatum) and possum-haw (V. nudum) are either very susceptible or susceptible to VLB. The only native ones that are moderately resistant are the nannyberry viburnum (V. lentago) and the blackhaw viburnum (V. prunifolium). On the other hand, many of the non-native species are very resistant. So I see our native plants being hit by a double whammy, first by the pest itself and second by nurseries selling “pest free viburnums,” meaning non-native ones.
Arrowwood, Viburnum dentatum
© Beatriz Moisset
The Cornell University site has a number of suggestions on how to fight this invasive pest starting with placing sticky traps around the base of the stems of shrubs in the spring to prevent the full grown larvae from crawling down to pupate. It is too late to do that now, so we will have to be ready next year.

Adult beetle
© Beatriz Moisset
The adults are active now, mid July, so I have been trying to collect them by shaking the branches, catching them on some white sheets underneath and dropping them in soapy water. I suspect that the numbers will grow larger in the next few weeks.

After the first frost it will be time to start inspecting the stems for signs of eggs and to prune and destroy infested twigs. They should be easy to identify thanks to photos in the mentioned sites. This is perhaps the most effective means of control, especially if your shrubs are relatively small. I fear that all these measures combined may not be enough to stop the advance of the VLB, particularly when there are many tall bushes among poison ivy and other shrubs; but we plan to do our best.
The sites listed also suggest some pesticides; but I haven’t considered those.
If worse comes to worse there are some soaps and oils that may be of help, especially in early spring when the young larvae are emerging from the eggs.

I hope that we can reduce the damage in our area so that birds passing by in the fall continue to find the nutritious berries of arrowwood and so moths also continue to find food.
I am interested in other suggestions. Have you detected this invasive pest in your gardens? I suggest that you look for the characteristic leaf damage and egg cases. Let us know if you find any.

Examples of native species highly susceptible to VLB:
  • Arrowwood viburnums (V. dentatum complex)
  • Possum haw or smooth witherod viburnum (V. nudum)
  • American cranberrybush viburnum (V. opulus var. americana; a variety of the European cranberry viburnum, V. opulus)
Examples of non-native species highly resistant to VLB:
  • Doublefile viburnum (V. plicatum). Eastern Asia
  • Tea viburnum (V. setigerum). Central and Western China
  • Siebold viburnum (V. sieboldii). Eastern Asia
  • Koreanspice viburnum (V. carlesii). Eastern Asia


Tuesday, February 21, 2017

Viburnum Under Siege

Leaf damage inflicted on arrowwood
by the viburnum leaf beetle
© Beatriz Moisset
 The shoots of Viburnum dentatum are thin, strong and straight. Native Americans used them for arrow shafts. That is why this shrub is often called arrowwood. Until recently it was considered as a plant free from serious pests. Now, the arrowwoods in my area are under attack by an invasive leaf beetle.

Last May (2010), I began noticing leaves full of holes (skeletonized); something that I have never seen before. I finally spotted the culprits, little bugs hiding on the underside of damaged leaves. They look somewhat like caterpillars, but not quite; they are greenish, with black dots. A visit to the Bugguide site helped me identify them and provided links to several university sites full of information (see below). They are the larvae of the viburnum leaf beetle (VLB for short, Pyrrhalta viburni), an introduced pest from The Old World. Both the larvae and adults of this beetle feed exclusively on a variety of species of viburnum.

Viburnum leaf beetle larva and leaf damage
© Beatriz Moisset
In its place of origin, probably eastern Asia, the beetle and the viburnum have been fighting an escalating war for perhaps as long as millions of years. The female lays its eggs in holes made on thin twigs of the plant and plugs the batches of eggs with sawdust and feces. The plant develops a thick and hard mass of scar tissue that crushes the eggs. The beetle fights back by producing larger and larger numbers of eggs, so that, at least, a few escape the crushing weapon. Also, several females lay their egg masses close together, overwhelming the capacity of the twig to develop scar tissue. The plant responds by getting better at making scar tissue. The struggle continues without serious damage to the plant and without either adversary going extinct. We could call it an armed truce.

In this scene enter the human horticulturists and their quest for exotic beauties to add to gardens, a noble endeavor it would seem. Who would have known the unintended consequences? It is easy to see how some beetle eggs were carried overseas along with nursery stock. When they arrived in this continent, it probably took them a number of years to make the transition from their familiar species of viburnum to our native ones; but, once they did it, they found a defenseless plant. None of our viburnum species had reasons to develop a defense weapon against an enemy that they had never met. They are easily overcome by the onslaught of the many hundreds of larvae that emerge from the eggs laid by each female. Healthy shrubs can be turned into gray skeletons in just a couple of years.

Adult viburnum leaf beetles
© Beatriz Moisset
 Annapolis Royal is a town in Nova Scotia that has been the port of entry for numerous kinds of horticultural stock, including some Asian and European viburnums, for more than a century. It has also been the site of a very important nursery. The viburnum leaf beetle was noticed for the first time, and soon forgotten, in the 1920s not far from this area. Not much happened until 1947 when it was collected and identified once again. And, for a second time, it was quickly forgotten, just a minor entomological curiosity. Another 40 years went by until the VLB and its damage to native viburnums began to be noticed in a number of places. Research and surveys began in the seventies and eighties with the object of studying the possibility of an invasion.

The spread of this pest has been gaining momentum since then. It is found in Canada and north eastern United States. Concern is growing, motivating some to say that this situation has the potential of “. . . verging on ecological disaster” (Small and Catling, 2005). The National Agricultural Pest Information System has been monitoring the advance of the beetle. They just added Montgomery county, PA, because of my finding. The story of the VLB is reminiscent to that of the chestnut blight and the hemlock woolly adelgid, to name just the best known examples of pests introduced with horticultural stock.

According to the USDA plant profile, there are 30 species of viburnum in the country, 15 of which are native. The others have been introduced from Europe or Asia. About half of the native ones are in the threatened or endangered category. Viburnum shrubs are present in our gardens and they also form part of the understory of many forests throughout North America. Their loss would be significant to wildlife. Their berries supply food for birds in the fall and winter. They are host plants for a number of moths, which in turn become food for baby birds. Among the moths that feed on viburnum we count the delightful hummingbird moth and the spectacular Io, imperial and cecropia moths.
In part II I will provide information on beetle identification and methods of control.

More Resources

Have you seen evidence of Viburnum Leaf Beetle in Your Wildlife Garden?

Viburnum Under Siege. Part Two

© 2011, Beatriz Moisset. First published in Beautiful Wildlife Garden, 2011

Wednesday, February 15, 2017

Pollinators and the Garden in Winter

Man-made bee houses
Good replacement for holes in old logs
©Beatriz Moisset
Do you ask yourself: where do pollinators go in winter? We see them through the warm seasons visiting flowers and doing their invaluable job. But, then what happens to them? Putting aside the few, such as hummingbirds and monarch butterflies, which fly to better climates, all the others find a secluded place to spend the cold months. Like hibernating bears, many fatten themselves by stocking up on supplies and then go to sleep. Others rest as eggs or in an immature state such as a larva or pupa. Either way, they need a sheltered space safe from predators, parasites and excessive cold.

I know that some gardeners, with the best of intentions, destroy these vital shelters. It may be a good idea to take a look at all the places used by pollinators during the winter. This is one case in which a little untidiness may be a good thing.

Most bees are ground nesters; this means that they build their nests in the ground, preferably a bare spot, dry and sunny and not subject to flooding. Sometimes there is a patch large enough for a whole town of nests; other times, just a few square inches of soil free from vegetation fill the needs of one enterprising bee raising a family. The mother bee dies at the end of the season, her mission accomplished. Her babies will emerge from the nests next spring.
Ground nest of a digger bee
©Beatriz Moisset

Not anthills but a small town of
Lasioglossum bees
©Beatriz Moisset

Bumble bees find some nook or cranny underground, perhaps under a tree root, a log, or even an old wall. The difference here is that the overwintering pollinator in this case is the adult, already mated and fertilized female which will start a whole new colony next spring.

One of my favorite bees, Augochlora pura, doesn’t nest underground. Instead it finds a dead log, whose bark is beginning to peel, and builds its nest under the bark. The younger generation emerges at the end of summer. They mate, and the new bees find shelter, once again, under loose tree bark. Many old dead logs serve as wintering shelter for this bee.

Two Augochlora pura females
getting ready for winter in November
©Beatriz Moisset

A sleeping beauty under bark in mid January
©Beatriz Moisset

Sleeping Beauty’s castle, old logs
©Beatriz Moisset
Other bees, including mason and leaf-cutter bees, use hollow twigs or holes dug by beetle larvae in trees. Bee houses that imitate these conditions are gaining popularity among gardeners and mason bees readily accept them. This is becoming a necessity in our suburban gardens, where old trees with beetle holes are rare. Clumps of dried grasses or the hollow canes of plants such as hydrangea or brambles are also valuable to nesting bees if they are allowed to stand through the winter and early spring.

Hollow twigs are a winter haven
to many pollinators
©Beatriz Moisset

Bees are not the only pollinators. Butterflies and moths do a good job too; so let us take a look at a couple of them.

 Fritillary caterpillars feed on violet plants. In the fall, when the adult butterfly is ready to lay its eggs, these plants are wilting or totally gone. The female lays its eggs near the remnants of violet plants or in the most likely places for violets to grow. Even if many eggs are lost, there are enough left to maintain the populations year after year. The curious thing is that the eggs hatch in the fall when there is nothing for the caterpillars to eat. So the tiny newborns bury themselves a little deeper and go to sleep until the next spring. By then, their food is ready and waiting for them.

Hummingbird moths (Hemaris), those colorful tiny pseudo-hummingbirds (I have seen many people fooled by them) have a different strategy. Their eggs hatch in the summer and the caterpillars feed on one of their favorite plants. They are not very choosy, from honeysuckles, to viburnums, to blackberries; all of them are good for the several species of hummingbird moths. In autumn, the fully grown caterpillar drops to the ground, buries itself under the leaf litter and becomes a pupa. Now it is ready for winter.

A patch of leaf litter serves as a winter home
to some pollinators
©Beatriz Moisset
Numerous variations on these general themes exist. Not just pollinators, but also a number of other insects, some of them beneficial predators of pest insects, take advantage of the mentioned wintering spots. We can conclude that: bare spots, dead logs, dried up grasses or other shrubby plants and leaf litter are all vital to pollinators and to other creatures, all of them important components of a garden ecosystem. The perfectly manicured garden may appeal to a certain idea of esthetics but it is a monstrosity from the ecological point of view. Some of us need to readjust the way we view a garden.

There is great beauty in the mechanism of how an ecosystem works. I relish this beauty so I find it easy to accept the visual impact of an “untidy” garden in need of some raking, re-sodding, log removal, leaf litter removal, etc.

Also see:
Helping Native Pollinators Winter Over Sierra Club

© 2011, Beatriz Moisset. First published in Native Plants and Wildlife Gardens, 2011

Wednesday, February 8, 2017

Winter Food for Birds

Field of Canada goldenrod. © Beatriz Moisset
 When the days get shorter and other signs of winter hang in the air, most birds pack their bags and leave for warmer climates. They are not necessarily running away from the cold weather, but from the lack of their favorite food, insects.

Not all leave; the ones that can make it through the winter on nuts and berries stay. Also those who know where to find insects stay. Woodpeckers belong to this latter category. Some, such as hawks and owls, who feed on other birds, mice and other small creatures, also stay.

The seed eaters, the most common winter birds, may not be strict vegetarians. They know how to locate some animal protein here and there and welcome these nutritional supplements when given a chance. It takes skill, sharp eyes, and perseverance because this kind of food is scarce and well hidden through the colder months. The winter landscape is devoid of flying insects or succulent caterpillars chomping on leaves. Whatever insect life there is, it is snuggled up under bark or soil. Or, if it is in plain view, it is hidden by color and shape, blending with the surroundings and holding perfectly still in the shape of eggs or cocoons.

Aphid and eggs on rose stem

Late December. ©Beatriz Moisset

At the end of the summer season, aphids produce eggs, minuscule ovals, glued to leaves or stems, so insignificant that we may fail to notice their presence. Sometimes chickadees are seen working their way up and down a rosebush stem nibbling at invisible tidbits. They feast on this snack, adding some protein to their drab winter diet.

Goldenrods supply an interesting insect food to winter birds. Some goldenrods present a peculiar round thickening about an inch in diameter half way along the stem called a goldenrod round gall. Some patches of goldenrods have numerous galls of this kind. They are easier to spot during the winter, when all the leaves are gone and the stems remain standing.

Goldenrod round gall produced by the goldenrod gall fly
©Beatriz Moisset
 How is a gall made? A fly lays an egg inside a goldenrod stem in the spring. Along with the egg, it injects some remarkable chemicals in the spot. The chemicals cause the stem to swell into a round tumor which becomes home and pantry for the growing larva. The maggot-like future fly sits in the heart of the growing gall feeding on the nutritious tissues and protected from enemies. By the end of summer it is fully grown, but it will not be ready to come out of this secure place until spring, so it sleeps through the winter curled up at the very center of its mansion.

Two birds seek these snacks in times of scarcity, downy woodpeckers and chickadees. They face a difficult task to get to their treasure. The gall has become as hard as wood. Cutting one open with a utility knife or a small saw is no easy task. Believe me, I have done it. I have also found and collected galls broken in by birds.

The woodpecker has a beak like a chisel. With surgical precision it cuts a clean hole. The chickadee’s tool, on the other hand, is not so efficient. So this bird has to labor hard, wrecking almost the entire gall to reach the center. It is easy to tell who the eater was by their distinctive signatures.

Goldenrod galls opened by birds

Downy woodpecker, left. Chickadee, right
© Beatriz Moisset
Wanting to learn more about birds in winter and their insect food, I went on a frustrating Google quest. I tried words such as “bird,” “food,” “winter,” “insect,” and “diet”. No matter what combination I used the overwhelming majority of hits referred to bird feeders and feeding. Even when I subtracted “bird feeder” and “feeding” from the search I failed to find studies on natural winter insect food. Doesn’t anybody study birds’ winter diet?

Finally I found a delightful exception by one of my favorite nature writers, Bernd Heinrich. A rigorous scientist and first class writer, his books for the general public are enjoyable as well as packed with solid information. I had read his Winter World: The Ingenuity of Animal Survival years ago and was happy to delve into it once again.

Chapter nine, The Kinglet’s Winter Fuel, tells us about the golden crowned kinglet and its means of survival in the harsh Maine winters. This delicate tiny bird feeds almost exclusively on insects. How does it manage at a time in which insects seem unavailable? Heinrich’s endless curiosity led him to answer this question after seeing these thumb-sized feathered wonders nibbling at apparently non-existing food near the tips of spruce trees. He caught a few and found their gizzards packed full of inchworm caterpillars. Determined to know more, he whacked a number of trees and gathered everything that dropped from them onto a white sheet spread on the snow.

He collected caterpillars along with a few other things. Eventually he managed to raise some of the inchworms and found out the moth they turn into at the end of winter. All this research took him several winters and the assistance of a number of his students; but he finally knew that kinglets depend on the “variant” moth for their winter survival.

I love the chapter’s closing line: “To care for the welfare of kinglets, it is necessary to care for moths.” Notice that he talks about moths, not bird feeders.

I often wonder about the proliferation of bird feeders and bird food in this country. I recognize their educational value and their importance in suburban and urban places where bird’s habitats are all but gone. But, I also wonder about the land devoted to growing bird seed. Perhaps, pesticides and methods to keep birds away are in use. Isn’t that another way of taking habitat away from wildlife? When we supply them with suet, do they neglect their insect-eating task? In short: Do we feed birds for their benefit or ours?
Woodpeckers at bird feeder
© Beatriz Moisset
In addition to bird feeders, we should remember that other ways to help birds include taking care of the moths, and berries and nuts, and, yes, dried up goldenrod plants and their round galls. In the long run, this may be the best way to feed birds.

© 2013, Beatriz Moisset. First published in Native Plants and Wildlife Gardens, 2013

Monday, February 6, 2017

Biocontrols. Fighting Fire with Fire

Mile-a-minute choking trees
© Beatriz Moisset
 What to do when an introduced species, be it a plant or insect, gets so out of control that eradication seems impossible? This is a serious consideration. We see it happens again and again. Many species are so entrenched that all efforts seem futile, from the most ecologically benign, such as physically removing the offenders, to the least desirable ones, the use of pesticides.

Part of the reason why some introduced organisms become invasive is that they left behind the enemies that kept them in check in their native lands. Once free from such restraints they can become enormously successful in their adoptive land. When other methods of control fail conservationists have been resorting to what I would call fighting fire with fire: bringing another introduced species to control the one that has become a pest. These are the so called biological controls or biocontrols. This method is a partial admission of defeat. It allows the invasive species to remain but minimizes its impact. The National Wildlife Federation says it best:
In vast natural areas such as the Everglades, where spraying, snipping or bulldozing exotic weeds is out of the question, a well-tested, well-behaved bug is the conservationist’s best weed whacker.
Vedalia beetle feeding on cottony cushion scale
© Matt Bertone
In the 1880s California citrus growers were desperate because an introduced pest, the cottony cushion scale (Icerya purchasi) was destroying their crops and nothing seemed to stop it, even burning infected trees. Scales are similar to aphids in that they feed on the sap of plants. This one, as the name indicates is coated with a white cotton-like material.

In desperation, they imported a lady beetle from Australia, the Vedalia beetle (Rodolia cardinalis). It adapted well to its new environment and went right to work bringing the pest under control and saving the citrus industry. This was the beginning of biocontrol introductions.

However, the method may backfire with disastrous consequences. At first, it was thought a good idea to bring biological controls with wide tastes. It turned out that some went after desirable bugs, not just the undesirable ones. One of the worst examples was a parasitic tachinid fly (Compsilura concinnata) brought in to control the gypsy moth. Unfortunately, it started feeding on many native moths including the spectacular Cecropia moth. Populations of some of these moths have dropped down enough to cause serious concern.
Cecropia Moth (Hyalophora cecropia)
© Marvin Smith. Wikicommons
It took some time to learn this hard lesson. Many biocontrols have created more problems than benefits. I mentioned the Chinese praying mantis and the Asian lady beetle in previous posts.

Nowadays the only biocontrols allowed are those with extremely narrow feeding habits, ideally only the target species. The U.S. Department of Agriculture approves biocontrols only after they have been subjected to thorough testing under tight quarantine conditions.

I will illustrate this with two examples that I have had the opportunity to observe: one controls an insect pest, the other a weed.

Japanese beetle with egg of parasitic fly
© Beatriz Moisset
The Japanese beetle has been advancing inexorably ever since it arrived in New Jersey hiding in some horticultural stock. Recently, a parasitic fly has been introduced to combat it. The winsome fly (Istocheta aldrichi) lays one or a few eggs on the back of the beetle. When the larvae hatch they penetrate the hapless insect and proceed to eat its insides. If you see a Japanese beetle with a white dot on its back, don’t kill it. Let the parasite complete its life cycle and live to infest other beetles.

Mile-a-minute weevils on mile-a-minute vine
© Beatriz Moisset
Mile-a-minute is becoming a terrible pest climbing up trees and choking them. Recently its biocontrol, a weevil, has been approved for distribution. The beetle is not much bigger than the tip of a ball point pen. It feeds on tender leaves. If you see holes in full size leaves, don’t look for the weevil there; instead follow the tendril to its end. This is where these voracious beetles hide. This introduction is so recent that we probably haven’t seen its full effect.

© 2015, Beatriz Moisset. First published in Native Plants and Wildlife Gardens 2/7/15