Boxwood Blight Found in Georgia

Edited from an article by Jean L. Williams-Woodward, Extension Plant Pathologist. Read the entire article here.

Boxwood or Box Blight, caused by the fungus, Cylindrocladium pseudonaviculatum (syn. Cylindrocladium buxicola and Calonectria pseudonaviculata) has been confirmed in two residential landscapes in the Buckhead area of Atlanta.

The source of the introduction to one of the landscapes is unknown as new boxwood plants were not introduced into the landscape. The spores of the pathogen are very sticky and it is possible that the disease was introduced on worker’s tools or clothing. Plants within the second landscape were newly introduced from NC. Once introduced, the disease can be devastating to boxwood in landscapes and nurseries.

Boxwood Blight 2 JWW
Boxwood blight infected dwarf English boxwood in GA showing tan foliage and dieback. (Image by Jean Williams-Woodward)

Hosts: Dwarf English boxwood (Buxus sempervirens ‘Suffruticosa’) is highly susceptible and develops severe symptoms and rapid leaf drop. American or common boxwood (B. sempervirens) cultivars are also very susceptible. Cultivars of Littleleaf (Japanese) and Korean boxwood (B. microphylla and B. sinica, respectively) appear less susceptible because they don’t show severe symptoms and leaf drop, but they are still susceptible.

None of the commercial boxwood cultivars are immune to this disease. In fact, lesser susceptible (e.g. tolerant) cultivars may act as a ‘Trojan Horse’ introducing the disease into landscapes containing more susceptible cultivars.

The value of lesser susceptible cultivars is in the establishment of new boxwood hedges. If planting a new area, use a more tolerant cultivar to lessen your disease pressure in subsequent years. The disease also affects other plants within the Buxaceae family, including Pachysandra terminalis (ground spurge) and Sarcococca sp. (sweet box).

Boxwood blight JWW
Boxwood blight symptoms clockwise from upper left: Tan to gray leaf lesions with a darker purplish border on an English boxwood; Circular, tan spots with a brown border on upper leaves; Tan blighted leaves and bare stems on an infected plant; blackening of stems and browning foliage; and black stem lesions on bare branch tips. (Images by Jean Williams-Woodward)

Management: The best control is exclusion. Do not introduce the disease on infected plants or tools. Inspect all new boxwood plants for symptoms of the disease. Be sure to check the lower leaf canopy and interior stems. Keep new plants isolated and separate from existing boxwoods. Do not apply fungicides to plants in isolation that would mask symptom development. Monitor plants for at least four weeks prior to introducing them into existing plantings.

If Boxwood blight is detected, the infected plants and all fallen leaf debris needs to be bagged on-site and removed from the area to be buried in a landfill to prevent its spread. Transport plants in closed bags. Leaf litter blowing from open trucks could spread the disease to plantings along the roadway. Fallen leaf debris should be vacuumed and bagged, burned on-site or buried. Debris should not be composted. The fungus also produces microsclerotia (small clump of fungal hyphae) within roots and leaf debris of infected plants that allows the fungus to survive for years. Removal of existing garden soil and replacing with new soil is an option, but there is no guarantee that this will completely remove the pathogen.

Boxwood blight cannot be controlled with curative fungicide applications. Fungicides are only effective when applied preventively. Fungicide efficacy trials have shown that fungicides containing chlorothalonil (Daconil, Spectro, Concert II) and fludioxonil (Medallion, Palladium) provided the best control when applied preventively. To a lesser extent, fungicides containing azoxystrobin (Heritage), pyraclostrobin (Pageant), trifloxystrobin (Compass), and thiophanate methyl (Cleary 3336, OHP 6672) provided fair to good preventative control. Most are not labeled for use on either boxwood, Cylindrocladium or both; however, this is changing, so check labels. Remember, spraying plants after the disease is present will NOT control this disease.

Recommendations for Landscapers:

  • Inspect boxwoods on all properties. Look for symptomatic plants. As weather patterns become conducive (wet, humid, warm), disease symptoms may become noticeable and spread rapidly.
  • Submit suspect samples to the UGA Plant Disease Clinic in Athens through county extension offices for disease identification.
  • Train employees and clients on how to identify boxwood blight. Educate them on how easily the disease spreads.
  • Only purchase plants from nurseries that have a Boxwood Blight Compliance Agreement through their State Department of Agriculture. Many plants are brokered, so ask where plants were grown. Keep new plants in isolation and monitor for symptoms prior to installation.
  • Never install or prune or work in boxwoods when plants are wet.
  • Always visit non-infected landscape sites first. Move healthy to suspect diseased areas; never the other way around.
  • Disinfect pruners and other tools frequently within and between different blocks of plants within the same landscape, and especially when moving to different landscapes.
  • The best product is Lysol Concentrate Disinfectant (containing 5.5% O-benzyl-p-chlorophenol). Mix 2.5 Tbsp per gallon of water. This can be made and kept in spray bottles. Tools need to be wet for at least 10 seconds and allowed to dry to be effective.
  • A 10% bleach solution (1:9 part Clorox or 1:14 part Clorox Concentrate) for at least a 10 second soak can also be used, but this will oxidize tools. Soak and then let dry.
  • When leaving a site suspected or known to have boxwood blight, all tools, shoes, and clothing must be disinfected.
  • Get in the habit of wearing clean disposable booties or washing off debris and dirt entirely from soles of shoes between landscapes.
  • Changing and laundering clothes between sites would be ideal; however, it’s impractical. Wearing disposable paper pants is an option.

Find more information here


Landscape Pop Quiz

Azalea lacebug Clemson University - USDA Cooperative Extension Slide SeriesThis is caused by Azalea Lace Bugs!

This information came from the publication Control of Common Pests of Landscape Plants 

Lace bugs get their name from the appearance of the area behind their head and wing covers. The area forms a lace like covering over the body of the insect. They are 1/8 to 1/4 inch in length and are partially transparent. Lace bug damage appears on the upper leaf surface as white to yellow chlorotic spots. The lower leaf surfaces will be cluttered with black spots and the old cast skins of immature lace bugs. Initiating control in the spring between March and May will reduce problems later in the season.

To find more id and control information on this or other landscape insects read the UGA publication Control of Common Pests of Landscape Plants 

To find pesticide recommendations and use information visit the Georgia Pest Management Handbook.

What’s the orange goo?

Jean Williams-Woodward, UGA Extension Plant Pathologist

I’ve been getting some calls and emails about “orange goo”  growing on cut hardwood stumps. It is weird, interesting and looks like an attack of ‘the blob” (see the image to the right). So, what causes the orange goo?

It’s the yeast, Cryptococcus macerans, growing on the sugary sap flowing from the cut branches or trunk. A few other fungi can also be found mixed in, including some species of Fusarium and Acremonium. The yeast is harmless to the plant; it is just growing on the sap.

The orange color comes from the pigment carotene, which is the same pigment that colors carrots orange. Some strains of Cryptococcus macerans could cause disease in humans, so if you can’t resist touching it, wash your hands! Generally though, it is harmless and just another interesting oddity in the fungal world.

Boxwood blight update

Jean Williams-Woodward, UGA Extension Plant Pathologist

Boxwood Blight is caused by the fungus, Cylindrocladium pseudonaviculatum, which causes leaf spotting, stem dieback, and death of almost all cultivars and species of boxwood. The disease moves quickly through infected plants, gardens, and nurseries.

It has been identified in 12 states (CT, DE, MA, MD, NC, NJ, NY, OH, OR, PA, RI, VA) and three Canadian provinces, and it is causing significant damage to boxwoods in those states, some in landscapes while others are restricted to nurseries. The pathogen also infects pachysandra (ground spurge) and causes similar leaf spots and stem dieback.

To date, Boxwood Blight has not been found in Georgia. However, introductions are possible on infected plants or on boxwood tip cuttings originating from out-of-state nurseries and suppliers.

Tan, circular leaf spots with a dark brown border develop within two days of inoculation. This is followed rapidly by the entire leaf turning brown, black lesions developing on the stems, and plant defoliation (see images). In some cases, time between leaf spot symptoms to plant death was two weeks.

This is a very damaging disease that you do not want in your nursery or landscape. The fungus produces white tufts of spores on the leaves and stems. The spores are very sticky and they will stick to pruning or digging tools, worker’s pants and hands, and dogs or other animals that may walk next to infected plants. In NC, wild turkeys were suspected of spreading the disease within field-grown boxwoods.

There is no control for this disease once it is present. The only control is preventing its introduction and preventive fungicide applications to protect non-infected plants.

Cylindrocladium diseases are difficult to manage with fungicides. Dr. Kelly Ivors at NCSU has conducted some fungicide trials against boxwood blight and has found that fungicides containing chlorothalonil (Daconil, Spectro, Disarm C, Concert II), fludioxonil (Medallion, Palladium) or tebuconazole (Torque) provided the best control when applied preventively. However, most of these products are either not labeled for control of Cylindrocladium or for use on boxwood or both. Pageant (pyraclostrobin and boscalid) is labeled for both boxwood and Cylindrocladium disease and provided fair to good preventive control. There is a great need for fungicide labeling changes and additions for this disease. Currently, fungicides are only needed in high risk areas where Boxwood Blight is known to occur. Spraying plants after the disease is present will NOT control this disease. Curative applications are ineffective.

If the disease is detected, the infected plants and all of its fallen leaf debris needs to be bagged on-site and removed from the area to be burned or buried to prevent its spread. In nurseries, propane torches have been used to burn any remaining leaf debris to rid the area of the pathogen; however, this may not completely control this disease.

The fungus also produces microscelrotia within roots and leaf debris of infected plants. Microsclerotia may allow the pathogen to remain viable at the site for years. Not to sound like an alarmist (but I have to here!), if I was in charge of a boxwood planting (box garden, topiary garden, historic plantation garden, nursery production, etc.), I would not bring in any boxwoods from anywhere. I would do all propagation in-house. You may think you are buying plants originating from a “safe” nursery, but in reality it could be a brokered plant that originated from an area where boxwood blight is present.

I also would not allow anyone to prune, shear, take tip cuttings, or touch my boxwoods if they have worked on boxwood somewhere else previously without first disinfecting their tools and changing their clothes. I’d rather make someone angry today, then for me to cry later because all my boxwoods are dead. Bottom line: You won’t get this disease if you don’t bring in any boxwoods. The spores are not wind-borne; they are water-splashed and carried on plants, people, tools, and animals. If you do bring in boxwood plants, make sure they come from a nursery certified to be free of Boxwood Blight.

Dr. Ivors has also conducted a Buxus cultivar susceptibility trial. Buxus sempervirens cultivars (English, American, Justin Brouwers, etc.) tend to be more susceptible. Buxus microphylla cultivars tend to be more tolerant of the disease; however, all cultivars can be infected. In fact, more tolerant cultivars could look asymptomatic, yet carry the pathogen (i.e. be a ‘ Typhoid Mary’), and spread the disease to surrounding susceptible plants. The value of cultivar susceptibility testing is in the establishment of new boxwood hedges. If planting a new area, use a more tolerant cultivar to lessen your disease pressure in subsequent years. See for more information on Boxwood Blight and links to Dr. Ivors’ research trials.

Fall is the time to plant and transplant trees and shrubs

Image credit, Krissy Slagle, UGA

By Merritt Melancon and Frank M. Watson , UGA Cooperative Extension 

Although most planting and transplanting occurs in the spring, fall is the best time of year to plant or transplant trees and shrubs.

“Trees planted in the fall have an opportunity to establish an extensive root system while the plant is dormant,” said Frank Watson, the University of Georgia Cooperative Extension coordinator in Wilkes County. “The soil temperature in most parts of the state is warm enough to support root growth during most or all of the winter season.”

Image credit, Krissy Slagle, UGA
Fall is the perfect time to install new trees or shrubs or remove existing ones to new locations. University of Georgia Cooperative Extension experts recommend digging the planting hole two to three times the diameter of the soil ball. Image credit: Krissy Slagle.

First make sure the trees or shrubs are healthy enough to plant in a new environment. If you’re buying new trees or shrubs from a nursery, make sure the trunk is not damaged, said Matthew Chappell, a UGA Extension nursery production specialist.

“If you see any damage to the bark, do not purchase (that tree),” Chappell said. The same goes for trees that are already on your property. You don’t want to stress an already damaged tree by transplanting.

Chappell added that picking trees with straight trunks and symmetrical canopies will save you a lot of heartache in the future. They’ll be easier to prune into a desired shape and typically are more structurally sound.

Also avoid purchasing pot-bound trees. Check the container for circling roots which indicate that the tree or shrub will have a poor root system after it’s been planted.

If you’re working with a tree that’s already on your property, help the plant take a break from producing new branches and leaves before transplanting. The plant can then put most of its energy into adapting to its new environment, not into producing new growth above the soil. Avoid applying high nitrogen fertilizers to plants for about two months prior to moving. Another way to reduce new growth is to restrict the amount of water applied. However, severe water stress prior to transplanting can weaken the plant and decrease the survival rate, Watson said.

In addition to having their growth restricted, transplanted shrubs and trees need to have their roots pruned. Pruning a tree’s roots — trimming them back until they fit inside the soil ball — maximizes the quantity of feeder roots that are moved with the plant. Ideally, plants targeted for fall transplanting would have their roots pruned the spring before they’re replanted, but they can still be pruned 30 to 60 days before transplanting in the fall.

Whether you’re working with a newly purchased plant or one on your property, it’s important to pay extra attention to preparing the plant’s new home. Properly preparing the planting site will affect root growth, which determines the plant’s chances of survival and subsequent growth.

The planting hole should be two to three times the diameter of the soil ball. Place the plant at the same soil depth it was grown at. If planting several small plants close together, it may be more efficient and better for the plant to prepare an entire bed.

When physically planting your shrub or tree, try not to disturb the soil ball of the plant. This will ensure maximum contact between the roots and the soil, which will speed the plant’s creation of its new root system.

A broken or loosened soil ball may prevent the plant from absorbing all of the water it needs. Wetting the soil around the shrub or tree can keep the soil ball together as you transplant. You may want to use wire baskets or other equipment that is available for moving plants.

Don’t plant trees and shrubs so that water pools on the surface of the planting hole. But remember, the plant will need extra water for the first two years.

Wait several months, maybe until the following spring, to fertilize the newly transplanted tree. This allows the root system to establish itself before spurring new growth above ground.

(Merritt Melancon is a news editor with the University of Georgia College of Agricultural and Environmental Sciences. Frank Watson is the University of Georgia Cooperative Extension agent in Wilkes County, Ga.)

Rose Rosette Virus – an emerging problem

Jean Williams-Woodward, UGA Plant Pathologist

Rose rosette virus is a damaging disease that is seeing an increase in occurrence across midwestern and southern states. Rose rosette has been described since the 1940s, but it wasn’t until 2011 that the causal agent was confirmed to be a virus spread by the ‘rose leaf curl’ eriophyid mite (Phyllacoptes fructiphylus).

Rose rosette disease on Knock-Out rose
Rose rosette disease on Knock-Out rose

Rose rosette virus was predominantly found in multiflora roses (Rosa multiflora) that now grow wild in many places and is considered an invasive/noxious weed. The wild multiflora roses were thought to be how the mite and virus spread into rose landscape plantings. What is causing greater concern is that the virus is now being seen in Knock-Out roses (see images). Knock-Out roses cover commercial and residential landscapes throughout the south because they are more disease resistance than other hybrid roses. The presence of the mass Knock-Out plantings provides an easy means for the mite and virus to spread from plant to plant and location to location. The increase in the amount of rose rosette showing up in Knock-Outs, which are all vegetatively propagated, has led to speculation that the virus may be spreading through nursery stock as well. This is possible, but currently I don’t have any evidence of this.

Symptoms of rose rosette virus mimic herbicide injury. In the past, we had no way of confirming the pathogen’s presence and often tried to rule out improper herbicide use. Symptoms include an increased and rapid elongation of new growth; abnormal reddish discoloration of shoots and foliage (see image above); witches broom (proliferation of new shoots); an overabundance of thorns; and deformed buds and flowers.

We are testing a molecular PCR test in the Athens clinic that can detect the virus RNA in order to confirm the disease. This test is the only way we can confirm virus infection.

If rose rosette virus is confirmed or suspected, control options are few. There is no cure for rose rosette. Roses growing near infected cultivated or wild (multiflora) roses have a high risk of infection.

To prevent infection:

  • Inspect new nursery stock for symptoms of infection.
  • Remove all multiflora roses from the area and increase plant spacing so rose plants will not touch each other to reduce mite spread.
  • If rose rosette is present, completely remove the infected plant by bagging and discarding or by burning.
  • There is some discussion on online garden forums and from rose breeders that just pruning off symptomatic canes/stems will remove the virus. There is not at present any scientific evidence that this will work. Therefore, the prudent recommendation I can give is to completely remove the infected plant.
  • A miticide can help reduce mite (and virus) spread; however, miticides labeled for spider mite control and those commonly packaged for homeowners are ineffective on eriophyid mites. If homeowners want to have their roses sprayed, then they should contact commercially licensed landscape professionals who can use (per communication with entomologist Will Hudson) Avid (or other abamectin generics), Floramite, Magus, and Forbid.