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:
http://www.ncagr.gov/plantindustry/Plant/entomology/EABProgram.htm
http://www.ncforestservice.gov/forest_health/fh_eabfaq.htm
http://www.emeraldashborer.info/files/E-2938.pdf
http://www.emeraldashborer.info/#sthash.nuLWCt3M.us4nCFGQ.dpbs

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 newpest@ncagr.gov. 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.

STEP 1.
Trim the branches off and cut the trunk into manageable sections.

STEP 2.
Snip the small branches up into a waste can and yard bags.

STEP 3.
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.

STEP 4.
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).

STEP 5.
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...

STEP 6.
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]

STEP 7.
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!

Monday, February 16, 2015

PDIC update: Winter weather schedule

The PDIC anticipates opening at noon on Tuesday, February 17 due to adverse weather. Check back for updates as our weather develops.

Wednesday, December 17, 2014

Pest Alert: Boxwood Blight on Holiday Greenery

Boxwood blight has been a problem in western North Carolina since it was first found here in the fall of 2011.  It has also affected boxwood in eleven other U.S. states and three Canadian provinces, and in Europe where it has been established for years. To date, boxwood blight has been a problem mostly in commercial boxwood production in North Carolina. We have seen only localized landscape outbreaks of the disease.

Leaves darkened and drying, falling from twigs. Dark streaks on green stems.
Boxwood blight on tips from a holiday wreath. Photo by Matt Bertone, NCSU PDIC.
The situation took a new turn this month with the discovery by the North Carolina Department of Agriculture and Consumer Services of boxwood blight in boxwood holiday greenery sold at retail stores in a few North Carolina locations. We do not know how widespread this disease is on boxwood tips sold for holiday greenery, but this alert is being distributed to avoid potentially irreversible damage to established boxwood plantings. It is written for purchasers of boxwood wreaths or other holiday greenery made from boxwood. Tip growers and nursery operations should consult with their local County Cooperative Extension Service or the NCDA&CS Plant Protection Section.

dark leaf spots and dark stem streaks, as well as leaf loss, are typical symptoms of boxwood blight
Dark leaf spots (left) and dark stem streaks and defolation (right) are typical boxwood blight symptoms.

Affected boxwood show three main symptoms:
  • dark leaf spots
  • dark streaks on green twigs
  • leaf drop. 
In some cases leaves will lose their luster and dry up without the typical spots, but this can happen for reasons other than boxwood blight. American and English boxwoods are particularly susceptible and are rendered unsightly by the disease, although they do not die.  Sarcoccoca (sweet box) is also affected. The fungus can infect Pachysandra, too, causing leaf spots that could go unnoticed.

Boxwood blight is caused by a fungus known scientifically as Calonectria pseudonaviculata. It also goes by the names Cylindrocladium pseudonaviculata and Cylindrocladium buxicola. The fungus is harmless to other kinds of plants, to animals, and to people.

lower leaves brown and fallen on boxwood-blight-stricken shrub
Defoliation typically begins near the base of the boxwood plant and moves upward. Photo by Kelly Ivors.
Calonectria pseudonaviculata can be spread long distances on infected plant material and could be moved on contaminated clothing, bags, footwear, tools, vehicles, etc. used by workers moving from field to field. Short-distance spread is by splashing water and potentially by animal activity. The sticky spores do not easily become airborne except by water splash. Infected wreaths and roping that are exposed to rains could be a source of the fungus for nearby boxwood, sweet box, or Pachysandra.  Greenery that is hanging in a sheltered area will pose little immediate risk, but leaves falling from them could be a source of contamination later on.

What should you do if you have boxwood greenery for the holidays? As a precaution, we are recommending the following:
(1) Inspect boxwood greenery for blight, and immediately discard suspicious material, including fallen leaves.
(2) If there are boxwood shrubs in your landscape and if any boxwood greenery has been placed in an area where it is exposed to rainfall, relocate the greenery or bag and discard it. Do not handle the material when wet, because you could easily spread the spores.
(3) At the end of the holiday season, bag up all boxwood greenery and dispose of it in a landfill. Do not place it in the compost.
(4) Monitor nearby boxwood plantings for symptoms of the disease.

More information about this disease, including more photographs, can be found on NCSU’s Plant Pathology Portal. The Virginia Boxwood Blight Task Force web page is also a good reference and includes lists of best management practices for different situations.

Friday, September 19, 2014

Almost-plague-level Liriope Munchers!!!

The red bricks of NCSU's campus are a nice resting pad for some grasshoppers with full bellies. 

As I walked back from lunch the other day, I stopped by the library to take a peak at a single, large grasshopper on a rail. It was a differential grasshopper (Acrididae: Melanoplus differentialis), and although I don't usually look at these common insects it was too conspicuous not to stop and admire. The next day our good friend Dave Stephan came to me to ask if I had good pics of the species. I said no, but figured "Why not?" So Dave, being the great person he is, collected some for me. The odd thing though was what they were feeding on:

A differential grasshopper sitting among the destruction it and its friends caused.

That's right, liriope or monkey grass (Liriope sp.)! This widely planted, grass-like ground cover is rarely ever attacked by pests. The most frequently encountered insect feeding on this ornamental is the fern scale, Pinnaspis aspidistrae. Otherwise I could only find reference to snails and slugs as animals that feed on this host. These grasshoppers must not know that they are not supposed to feed on it, because there were hundreds in the large patch on campus! But why? We really don't know. I am also unsure if they will feed on the related lilyturf or mondo grass (Ophiopogon sp.).

Male Melanoplus differentialis, the differential grasshopper.

Female differential grasshopper.

Differential grasshoppers are typically pests of field crops like soybean, corn and cole crops, but also feed on many grasses and other plants. They can become serious pests in some areas during certain years. Their large size (about 2" long) also makes them conspicuous and also very hungry! Keep an eye out and let us know if you notice them feeding on liriope (or mondo grass) - perhaps this is an isolated event, but we don't know for sure.