Friday, September 4, 2015

Boxwood Blight Active Again

After a lull of several months, samples of suspected boxwood blight have been coming to the NCSU Plant Disease and Insect Clinic (PDIC) over the course of the last month. Just this week we’ve had confirmation on samples from a garden center in Macon County, North Carolina, and home landscapes in Transylvania, Jackson, and Forsyth Counties.
Symptoms of boxwood blight at a garden center. Photo: Alan Durden, NCCES

This news is disheartening for two reasons. First of all, the find in Winston-Salem follows concerted efforts to stamp out the 2013 outbreak there. Secondly, the other confirmations this week represent the first reports of boxwood blight in our southern mountain counties of North Carolina.

Landscapers, homeowners, nurseries, and garden centers should be alert for symptoms of boxwood blight: brown leaf spots, black streaks on green twigs, and leaf drop, usually starting in the lower portions of the plant. As we move toward the holiday season, individuals and businesses that cut boxwood tips for wreaths and other greenery should be sure they understand the implications of this disease for their industry.
Leaf spots, stem streaks, and defoliation typical of boxwood blight.

Comprehensive sets of recommendations are available from the Virginia Boxwood Blight Task Force. Those publications mention Virginia’s “Boxwood Blight Cleanliness Program”. The equivalent for North Carolina is the NC Department of Agriculture and Consumer Services, Plant Industry Division, Plant Protection Section's Boxwood Blight Compliance Program for nurseries.

It is still the policy of the PDIC that samples submitted by nurseries for boxwood blight confirmation only will be processed at no charge; however, we recommend submitting them through the NC Cooperative Extension Service or the NCDA&CS.

Thursday, August 27, 2015

Are Asian or Japanese giant hornets in the United States?


But there is a lot of fear of them. It could be from news reports out of China stating death tolls in the dozens, or natural history videos depicting them massacring thousands of honey bees. They certainly are vicious insects with an aggressive reputation, but plaguing North Carolinians (or other Americans)? It's not happening.

Here's a little background on these wasps. The family Vespidae has a large diversity of forms and social structures and is found throughout the world. Many species are solitary, preferring to work alone to provide nests and food for their young - food typically being other insects (as in the Eumeninae; see image below left) or pollen (as in the Masarinae). The familiar paper wasps make up the subfamily Polistinae (see image below right), and are social but usually have small to moderate-sized colonies. Many build open nests out of paper made by gathering pulp from dried wood. They are often seen under the eaves of homes in our area and, while they can be aggressive, are often tolerant of people. They are also beneficial predators of many garden pests.

Potter wasps (left) and paper wasps (right) are two familiar groups in the family Vespidae. Note how members of this family fold their wings lengthwise at rest. Photos by Matt Bertone.

The subfamily Vespinae encompasses species with the largest colonies (numbering in the hundreds to over one thousand individuals) and contains the subject of this article. Some are small wasps that typically build paper nests in the ground, including the well-known yellowjackets (Vespula spp.; see image below). Others, generally called hornets, build large paper nests in the open or inside dead trees, attics or other hollow structures. Hornets and yellow-jackets are highly aggressive toward perceived threats and, thus, have a bad reputation. Among the vespines, the largest wasps are in the genus Vespa. This genus has 23 species native to Europe, the Middle East, NE Africa, and Asia (most diverse in SE Asia); there are no native Vespa in the Western Hemisphere. Like many other members of the subfamily, the adult wasps will hunt and dismember prey (even scavenging carrion) to feed to their young, while taking sugary meals of ripe fruit or oozing tree sap for their own energy.

Yellowjackets (like this Vespula maculifrons du Buysson) are small to medium wasps that typically create nests under ground. Note the notched eye, characteristic of Vespidae. Photo by Matt Bertone.

The largest are Asian giant hornets (Vespa mandarinia Smith; see image below) also called yak-killer hornets and including a subspecies called the Japanese giant hornet (V. mandarinia japonica). Workers average about 3.5 cm, but queens can be a whopping 5.5 cm with a 7 cm wingspan! These wasps, as alluded to above, are very aggressive and pack large quantities of potent venom. While the LD50 of V. mandarinia is 4.0 mg/kg (on par with the toxicity of some venomous snakes), it is actually less toxic by volume than our native southeastern yellowjacket, Vespula squamosa (Drury), with an LD50 of 3.5 mg/kg. However, the volume of venom injected and some necrotic and hemorrhagic properties of the venom make this hornet dangerous. The biology of Vespa mandarinia, especially related to their attacks on honey bees, was outlined thoroughly by Matsuura and Sakagami (1973).

The Asian giant hornet (Vespa mandarinia) is a large wasp found in many parts of middle and southern mainland Asia and nearby islands. This specimen measures just over 3.5 cm (not including the stinger), and in life would have a vibrant yellow/orange head and stripes on a dark brown or black background. Note that the eyes are very far from the back of the head, almost twice the distance as the width of each eye - a characteristic of this species. Photo by Matt Bertone.

So what are people seeing when they think one of these monster killer hornets is on the loose? There are two main suspects found in the Eastern US that are often confused for Asian giant hornets. The first is actually a close relative, the European hornet (Vespa crabro L.; see images below). This species was introduced from Europe/Asia into the US sometime in the 1800s and first recorded in NY. It has since spread across much of the eastern half of the US. These wasps tend to nest in tree cavities and prefer to be away from humans, but sometimes are found in other situations, even in attics or walls of homes. They can be aggressive and have painful stings, but are not usually an issue to homeowners.

In life, European hornets (Vespa crabro) have a mix of yellow, black and reddish-brown colors.
European hornets (Vespa crabro) have a much darker head with larger eyes than Asian giant hornets. They also have wider yellow stripes with black markings on their abdomen. This specimen is about 3.0 cm in length. Photo by Matt Bertone.

Another candidate, and a wasp that is even larger than any hornet we have here, is the Eastern cicada killer (Sphecius speciosus (Drury)). These wasps are distantly related to hornets. They are in fact a type of solitary hunting wasp in the family Crabronidae (formerly a part of Sphecidae, which contains familiar wasps like mud daubers). As their name implies, cicada killer wasps hunt cicadas. In mid-summer, males guard plots of ground suitable for tunnels and may "attack" any intruder, especially other males. However, they cannot sting. It's the females that find this prey and paralyze it, not for her own food but for her young (larvae) to consume. Once a female has paralyzed her cicada, she buries it in the ground and lays an egg that will hatch into a larva that will consume the prey. Although they have an impressive stinger and have venom, they are not aggressive and prefer to avoid conflict - after all there is no one to do the work if they die! If you can get them to sting (which would take a lot) they apparently cause very mild pain, especially for their size.

Eastern cicada killers (Sphecius speciosus) prefer to be hunting cicadas or digging in the ground than swarming or attacking. They are solitary by definition, but sometimes nest in large aggregations, somewhat like an apartment building. Note the large, unnotched eyes and wings that are not folded lengthwise at rest.
The Eastern cicada killer wasp (Sphecius speciosus) is an impressive insect. It has to be, though: females must attack and wrestle down cicadas to paralyze and bury for their young. Note the large, round eyes with no notch and elongate, pointed abdomen. Photo by Matt Bertone.

In conclusion, although you may see a large and scary wasp out and about, the likelihood of it being an invasive Asian giant hornet is zero. The two giant wasps we have are impressive, but not very surprising or dangerous (basically harmless in the case of cicada killers). Finally, for comparison, here is a photo of all three next to each other:

Three giant wasps, the first of which you will not see in the US: A) Asian giant hornet (Vespa mandarinia), B) European hornet (Vespa crabro), C) cicada killer (Sphecius speciosus). Photo by Matt Bertone.


One final thought: despite lacking "killer" Asian giant hornets, every year dozens of people in the US die from wasp stings (including those from honey bees, Apis mellifera L.). These are largely attributed to allergic reactions, but in some rare cases that involve extremely large numbers of stings, the venom itself can have lethal effects. It is always good to be careful around any stinging insect, especially those that live in large colonies that might be vigorously defended. People who are allergic should always have an epinephrine autoinjector ready when working around such insects. If you have a large wasp nest that appears too difficult to control, it is best to hire a professional to take care of the nest. For more information on control of these wasps, see this note on Dolichovespula and Vespula, and this note on Vespa crabro.

Helpful resources:

Friday, June 5, 2015

A Rope of Maggots

- Science, 1894

Dark-winged fungus gnat larvae are worm-like creatures, each translucent white with a black head and not a single leg on their body. They usually squirm their way around alone or in small gangs, in wet leaf litter, rotten logs, compost bins, potting soil and, of course, fungi. They feed on decaying materials in hopes of someday becoming a winged fly, ready to mate and make more larvae.

The black head is all that keeps this fungus gnat larva from resembling a true worm.

But when conditions are right (or maybe wrong for the larvae) they become something more.
They become snakeworms. Army worms*. A rope of maggots:

A mass of fungus gnat larvae (Sciaridae) from Craven Co., NC (Photo: Thomas Glasgow)

It's hard to judge the oddity from afar, because it just looks like a giant worm or snake. But closer up you can see that this pulsing mass is made up of hundreds or even thousands of these young fungus gnats:

Close up of the mass. (Photo: Thomas Glasgow)

Photos don't really do the mass justice, especially because of the way it moves. To get a good idea of the motion of this ocean [of maggots], just watch this video (be warned: it's not for the squeamish). These masses can attain many feet in length. Sometimes the group splits; other times groups fuse. In a display of futility, the "head" sometimes even follows the tail, the whole unit creating a writhing merry-go-round.

At this point you are probably asking WHY are these critters doing this? Well, nobody really knows. The phenomenon is recorded from all major continents and displayed by many species. In Europe, for example, Sciara militaris is well known and named for its behavior of marching in ranks. These gregarious larvae seem to grow in unison and then migrate together. If I had to guess, I would say that they are going together to a site for either better food or to pupate. I also imagine that alone they would quickly dry out or be eaten, but these convoys allow the larvae to move more efficiently and in a safer (and moister) manner. Whether this occurs normally depending on the species, or it is simply an opportunistic behavior determined by certain abiotic factors, I am not sure. But I have even seen photos where larger maggots of other flies travel with these gnats, which means it's not only the fungus gnats who think it's a good idea.

Although disturbing, these masses are harmless and merely an interesting survival strategy. Once safe and left to pupate, the larvae may turn into small drab flies or into the more impressive orange and black sciarids seen here:

Mating pair of Odontosciara nigra (male left; female right), a conspicuously large and colorful early summer species here in North Carolina.

Let's just hope they don't skip right to becoming giant militaristic, worm creatures with armor plates and pulse cannons.

* not to be confused with armyworm caterpillars (Lepidoptera: Noctuidae)

UPDATE: Debbie Roos has a nice blog post about these fungus gnat larvae (which can be pests in greenhouses) that shows a mass with another type of maggot tagging along.

Friday, May 22, 2015

Bacterial Blight of Geranium

For the first time in several years, the Plant Disease and Insect Clinic received a sample of geranium with bacterial blight caused by Xanthomonas hortorum pv. pelargonii (formerly Xanthomonas campestris pv. pelargonii) from a North Carolina greenhouse. All geranium (Pelargonium) producers should be vigilant.

Small, circular necrotic spots and also larger wedge-shaped marginal lesions.
Typical leaf symptoms of bacterial blight of geranium.
In this case the submitted leaves showed small circular leaf spots and v-shaped necrotic lesions at the leaf margin. There were also edema-like bumps on the underside of the leaves. Petioles appeared healthy in this case, but in the advanced stages of this disease, stems can become infected, resulting in wilting. Note that with bacterial wilt caused by Ralstonia solanacearum there is no leaf spotting.

Small scabby spots and also typical triangular lesion at the margin.
Close-up of upper leaf surface of Xanthomonas-infected geranium.
Water splash, tools, and handling are possible ways this pathogen can spread, and of course through infected propagative material (stock plants or buy-ins). Fortunately this strain of Xanthomonas does not affect any plants other than geranium, though it could survive in infected debris. Avoid overhead watering as much as possible. Keeping plants grouped by source can be helpful in containing and tracing any outbreak that occurs.

When Xanthomonas blight is confirmed in a geranium crop, the affected plants must be discarded, including the potting mix. Workers should avoid working among healthy geraniums after handling diseased plants. Asymptomatic (apparently healthy) plants next to diseased plants should also be destroyed, since they likely have populations of the bacterium on or in their tissues. The same goes for geraniums grown under hanging baskets containing diseased geraniums. All surfaces that had been in contact with these plants should be cleaned and then sanitized. This includes benches, tools, and pots. There’s a table with detailed information about sanitizers in the "Nursery Crops" section of the Plant Pathology Department Ornamentals page.

Preventive applications of a copper-based fungicide/bactericide, rotated with the biological control Bacillus subtilis, may reduce the spread of bacterial blight, but is not an effective strategy on its own. Use of clean stock and rigorous sanitation are the essential steps. For details on chemical applications, see p.448 of Table 10-11 in the 2015 North Carolina Agricultural Chemicals Manual.

For more information, see the following publications:
Bacterial Blight of Geranium by Gary Moorman of the Pennsylvania State University
Bacterial Blight of Geranium by M.B. Dicklow of the University of Massachusetts

A special thank-you to Dr. Mike Benson for reviewing this post.

Friday, April 10, 2015

Rose Woes

Diseased Knock Out Rose received in the Clinic
This week the Plant Disease and Insect Clinic at NCSU received a container rose with both downy mildew Botrytis blight. Both are favored by cool, moist conditions, and both can cause extensive damage in a short period of time under production conditions, via the dispersion of airborne spores. That’s where the similarity ends.

Cankers caused by Botrytis on rose canes are often light in color. This same fungus can cause spotting on rose petals and in the present case grew all over clusters of dead new leaves. It enters plants most easily in senescent tissue or through wounds. Recent cold snaps may have given Botrytis a leg up. On the other hand, downy mildew needs to infect and reproduce on living plant tissue. On rose leaves, it typically produces dark angular spots, though here it was found on green leaves that showed only a very slight mottle. On canes the usual symptom of rose downy mildew is purple or black blotching or spotting.

The downy mildew pathogen was found sporulating on the underside of this fairly healthy-looking leaflet.
Botrytis is sometimes called gray mold. This color is the combination of the black of the tiny thread-like stalks (conidiophores) and the white of the spores (conidia). Under magnification these look like pompoms. The spores of rose downy mildew (Peronospora sparsa) may or may not be visible on an infected plant. They are especially scarce on canes. On leaves they will be produced on the underside only. These structures are slightly smaller and more delicate than those of Botrytis, and the stalks (sporangiophores) are white.  They branch repeatedly giving a more open, tree-like growth. At the tips of the sporangiophore’s branches, spores (sporangia) appear white or tinged grayish blue in mass.
Sporulation of Botrytis on a rose cane. Note the thorn in the upper right for size comparison.
Close-up of Botrytis sporulation. Sometimes a second "pompom" of spores will form in the middle of the conidiophore.
Sporulation of Peronospora sparsa. It’s unusual to see so much on a cane.
Close-up of Peronospora sparsa sporulation. This and the previous three photos courtesy of Matt Bertone.
Prune out any affected canes you find, going well into clean wood. Sanitize shears frequently. Do not let debris or spent flowers accumulate, as Botrytis can reproduce on just about any kind of dead plant material. Keep foliage and stems as dry as possible by proper timing of irrigation and adequate plant spacing to allow good air movement. One reason these fungi were doing so well on this sample may have been that the plants are still in a greenhouse-like environment.

This time of year rose growers should maintain a spray program that includes products against both pathogens. Since the pathogens are unrelated, some products work only on one or the other. See pages 465-467 of Table 10-13 of the NC Ag Chemicals Manual. See also Table 10-14 (pp. 474-476) on relative effectiveness of different products. Follow all label directions. Remember that labels can vary depending on whether the plants are being grown outdoors or in an enclosed structure such as a greenhouse. Be sure to rotate among fungicides in different FRAC groups so as to delay the development of resistant strains. Test any new product on a small number of plants to be sure that there are no adverse effects.

Note: Early indications are that the plant pictured above also has a bacterial disease called Pseudomonas blight. Symptoms of this disease include cankers on stems and the death of new shoots, often following freezing temperatures. It affects not only rose but a wide range of woody hosts. Plants like this one are best discarded. For details, see last year’s blog post.

Wednesday, April 1, 2015

Emerald Ash Borer in Wayne County

The emerald ash borer has been found in Wayne County North Carolina. Other counties where EAB has been reported include Granville, Person, Vance and Warren.

 Links to EAB information:

Homeowners and landowners are encouraged to report any symptomatic activity in ash trees to the NCDA&CS Plant Industry Division hotline at 1-800-206-9333 or The pest can affect any of the four types of ash trees grown in the state.

Tuesday, March 10, 2015

How an Entomologist Does Yard Work

The day this post was born was very different from the one that jump-started the whole thing. You may have seen my post on our Facebook page showing a ca. 25-30' eastern red cedar (Juniperus virginiana) that fell from a heavy coating of freezing rain a couple weeks ago:

Poor tree couldn't take it :(

It was not an ideal situation for our yard, and certainly not for the tree. But I couldn't deal with it due to on and off snow for two weeks.

THEN THE SUN EMERGED!!!! During a warm and sunny afternoon this past Sunday I (with a newly purchased chainsaw) was ready to tackle this tree.

Trim the branches off and cut the trunk into manageable sections.

Snip the small branches up into a waste can and yard bags.

Start to see little flying insects glimmering in the sun over the pile of remaining branches. Also start to get excited - what are they? Go and get the insect net to sweep some critters under the ire of my wife who is attempting to do real work.

This net is not necessary for getting rid of a tree unless you are an entomologist.

Sweep. Unsuccessfully, but then something! But I need a vial! Run into house to get a vial. See that they are beetles. Also see some flies including dark-winged fungus gnats (Sciaridae) and some kind of acalyptrate fly (perhaps Drosophilidae).

Continue to "work" by cutting up the branches. Notice more and more beetles landing on the waste bag and pile of logs. Continue to collect (and work). Convince wife to go for a run so she doesn't roll her eyes right out of her head. After a little more collecting, vial is full to my satisfaction - so back to work.

I'm actually doing yard work - see the pruners in my hand? Oh and a vial full of beetles...

Clean up time. But what's this? Roll over one of the logs to see a beautiful beetle sitting still. Run in to grab the camera. Take some photos and capture the beetle to identify. Back to work cleaning up.

This is no ladybug - it's a curious longhorn beetle, the cedar tree borer (Cerambycidae: Semanotus ligneus). Note the necklace of phoretic mites. [Size: 10 mm]

Yard is done to our satisfaction for the day. Enjoy a beer and dinner.


So what were the little flying beetles? When I saw the first specimen I though it may be a member of the very strange darkling beetle genus Rhipidandrus, but upon closer inspection I knew they were some kind of bark beetle. After keying them out they had a name: Phloeosinus dentatus (Curculionidae: Scolytinae), a species known to colonize various Cupressaceae including eastern red cedar.

Little beetles like this Phloeosinus dentatus always interest me. [Size: 2.5 mm]

I was somewhat surprised with the speed at which these beetles began to arrive. It was late afternoon and only took about 20 minutes of cutting before they smelled the distinct odor of cedar. About two dozen landed around the various piles of wood. These beetles, although having relatives that are detrimental to our trees and landscape, are important decomposers of trees and their activities help to begin the process of decay in forests. They are also monogamous and create nice galleries under bark in which they and their larvae live and feed.

And now for a couple more photos:

Cedar bark beetle (Curculionidae: Scolytinae: Phloeosinus dentatus)
Cedar longhorn beetle (Cerambycidae: Cerambycinae: Semanotus ligneus) 

Tuesday, February 17, 2015

PDIC update: closed today, Tuesday February 17, 2015.

Due to adverse weather, NCSU and the PDIC are closed today, Tuesday February 17. Check back for weather-related updates as they become available. Be sure to read our recent posting on how to protect samples from cold when you ship them to the PDIC. Stay safe!