Richard Buckley

June 13, 2023 Richard Buckley

Got leaves?

Have you taken a look at your sycamore lately? Seeing any leaves this spring? Looks like a little problem!

brown, angular leaf spots on plane tree leaves

Classic angular leaf spot and twig blight of sycamore anthracnose. Photo: Richard Buckley, Rutgers PDL

Samples of deciduous shade trees diagnosed with anthracnose have steadily found their way into Rutgers Plant Diagnostic Laboratory this spring. Anthracnose is a common fungal disease of shade trees that results in angular leaf spots, cupping or curling of leaves, and premature defoliation. Green stems and twigs can become infected, causing twigs to dieback and overwintering cankers to form. We’ve had samples of sycamore and London plane tree, but have also had ash, beech, maple and a bunch of oaks.

water-soaked, necrotic spots on distorted ash leaves

Ash anthracnose causes necrotic spots and distorted leaves. Photo: Richard Buckley, Rutgers PDL

The fungi responsible for anthracnose in shade trees are all unique. The fungus that attacks sycamore is not the same as the fungi that cause ash, beech, dogwood, maple, or oak anthracnose. Each tree species has a specific fungus causing its own anthracnose disease, so for example, the beech anthracnose fungus does not infect oaks and the oak anthracnose fungus does not infect maples and so on.

brown, angular spots on silver maple leaves

Marginal necrosis and irregularly-shaped, angular leaf spots on silver maple (Acer saccharinum). Photo: Sabrina Tirpak, Rutgers PDL

Infections by anthracnose causing fungi are favored by cool, wet conditions during the budbreak period in the spring. When the weather favors one of these fungi, it generally favors all of them, so we see the disease to some degree on many different hosts. Anthracnose fungi survive winter in buds, small twig cankers, or fallen leaves depending on which types of trees and fungi are involved. In the spring, the spores are moved by wind and water to newly forming leaves. The longer the weather conditions remain cool and wet, the more damage one can expect. Once the weather becomes dry and the leaves mature, the disease cycle ends and the tree will replace lost leaves with new ones.

Beech anthracnose. Photo: Sabrina Tirpak, Rutgers PDL

Anthracnose can cause a very visible leaf lesion, and depending on the fungus/tree species dynamic, may defoliate the tree. Sycamore anthracnose causes a very significant defoliation, while beech anthracnose rarely does. Furthermore, it is not uncommon for the causal fungus to kill the buds before they open in the spring. It’s also not uncommon for the fungus to kill new green stems and twigs. Although these diseases often seem severe, they have little long-term impact on overall tree health. Leaves and buds damaged early in the season are often replaced by mid-summer.

Small spots with yellow borders and distorted leaves, caused by oak anthracnose. Photo: Sabrina Tirpak, Rutgers PDL

So, what do we do about anthracnose? Not much, really! Rake and remove fallen leaves. Improve plant vigor with fertilization and irrigation in times of drought, and prune all of the dead and dying limbs. Fungicides can be used to prevent the problem in high-value trees. Begin treatments at budbreak to protect the new growth and repeat the treatments 2-3 times at the label specified intervals. Proper timing and good coverage are essential, which will necessitate a licensed professional applicator to make the applications.

By the way, it is too late for fungicide protection this season!

Fungal diseases in most ornamental plants can be prevented with applications of one or a combination of the following active ingredients: FRAC M3 mancozeb; FRAC M5 chlorothalonil; FRAC 1 thiophanate-methyl; FRAC 3 metconazole, myclobutanil, propiconazole, tebuconazole, triademefon, triflumizole; FRAC 7 boscalid, flutolanil, oxycarboxin; FRAC 11 azoxystrobin, fluoxastrobin, kresoxim-methyl, pyraclostrobin, trifloxystrobin; FRAC 12 fludioxonil; and/or FRAC 19 polyoxin-D. Be sure to follow all label specifications for the host plant, the specific diseases controlled, as well as rates, dilution, and timing.

Filed Under: Landscape, Nursery, & Turf, Plant Diagnostic Lab, Uncategorized Tagged With: anthracnose, Plant Diagnostic Laboratory, shade trees

May 17, 2022 Richard Buckley

Leaf Spot and Melting Out……of Pachysandra?

Last week’s post concerning leaf spot diseases in turfgrass, and a few samples of dead pachysandra in the lab this week, got me thinking about how much I hate pachysandra. Hate might be too strong a word for a plant, but like Neumann and Jerry, this subshrub is my nemesis. Some of you may have heard me tell stories about trying to rid my home garden of pachysandra and finding it impossible to kill, but subsequently planting several hundred plants at my late-mother’s house only to see them all die of disease, so surely you can empathize with my perspective!

Pachysandra can grow in deep-shade areas, so it is well-suited and popular as a ground cover for shade gardens. The most commonly used species is P. terminalis, the Japanese spurge, which is an aggressively spreading evergreen. It is very deer-resistant, which unfortunately, also means that it gets planted into many New Jersey landscapes and gardens for that reason alone.

Deep shade usually means a wet site and that is where the disease issue comes in. Pachysandra, especially P. terminalis, is susceptible to the fungus Pseudonectria pachysandricola, which is the cause of the disease Volutella Leaf and Stem Blight. Leaf and stem blight is the most destructive disease of pachysandra in New Jersey.

Photo 1: Leaf spot phase of Volutella Leaf and Stem Blight. Photo: Richard Buckley, Rutgers PDL

Numerous patches of wilting and dying plants in a landscape bed are often the first indication that Volutella blight is in active in the bed. Both leaves and stems are attacked by the causal fungus. Leaves develop irregular tan to brown blotches, often with concentric circles of light and darker zones and sometimes with dark-brown margins. These blotches gradually increase in size until the entire leaf turns brown or black and dies. Stem cankers usually develop and cause whole plants to die back. Stem cankers can appear at any point on the stem and begin as greenish-brown and water-soaked lesions that eventually turn brown or black as the stems shrivel. As the fungus girdles the stem, sizeable parts of the plant beyond or above that point turn brown and die. Plant death from stem infections can be quite extensive, so the planting appears to melt away in a manner very much like turfgrass subjected to leaf spot and melting out.

Photo 2: Stem infection of Volutella Leaf and Stem Blight. Photo: Sabrina Tirpak, Rutgers PDL

Photo 3: Melting out of a Pachysandra planting due to Volutella Leaf and Stem Blight. Photo: Richard Buckley, Rutgers PDL

During wet, humid weather, affected plant parts can be covered with reddish-orange, cushion-like fungal fruiting bodies, called sporodochia. Conidia (asexual spores) produced in the sporodochia disseminate the fungus within the planting. They are easily spread by rain splashing and wind, or mechanically by people working the bed during wet weather. If blight is suspected, but fruiting bodies are not evident, place suspect plant material in a plastic bag with a moist paper towel. In a day or two fruiting bodies will develop that can be seen with a hand-lens.

Weak or injured plant material is much more susceptible to the disease than healthy tissue, so damage may be very severe when plants have been stressed by excessive sunlight, winter injury, drought, or insect attack. Spread of the fungus is also more rapid in dense plantings, where heavy mulches are used, or in beds with residual leaf debris. Planting beds subject to regular overhead irrigation often have more disease activity.

Photo 4: Winter injury to Pachysandra. Photo: Dr. Ann Gould, NJAES

Photo 5: Euonymus scale on Pachysandra. Photo: Richard Buckley, Rutgers PDL

Normally this disease does little damage to vigorous plants, thus providing good growing conditions is one of the most important control measures. Begin by selecting healthy, disease-free planting materials. Plant in a well-drained soil and on sites with suitable sun/shade exposure.

Control of the disease in an infected planting bed begins with good sanitation. Remove and destroy all of the affected plants and plant debris. Use a regular lawn mower set at a 1 to- 2 inch cutting height to mow the affected area. Catch all of the debris in a bag and discard. Be sure to mow an area well outside of the diseased patch. A little nitrogen fertilizer will help the remaining plants to fill in the mowed area.

Prune trees and shrubs to increase light penetration and air circulation in and around the site to help keep it dry. Avoid overhead irrigation and avoid wet foliage whenever possible. If irrigation is needed to avoid drought stress, then water early in the day, so the foliage can dry as quickly as possible.

On high value landscapes, and after sanitation and moisture management issues are corrected, fungicides may be an effective addition to a management program: make applications of chlorothalonil, copper, mancozeb, myclobutanil, or thiophanate-methyl at the first sign of disease and repeat at label specified intervals and rates.

I’ll leave you with this existential question: are you sure you really want to plant pachysandra? How about a hosta or something instead?

Filed Under: Landscape, Nursery, & Turf, Nursery, Plant Diagnostic Lab, Turf

May 12, 2022 Richard Buckley

Spring (and Summer) Leaf Spot Diseases in Lawns and Sports Turf.

Spring and early summer bring leaf spot diseases to cool-season grasses in home lawns, parks and grounds, on sports fields, and occasionally on golf courses. These diseases are caused by several fungi in the genera Curvularia, Bipolaris and Drechslera. Every cool-season turfgrass species has at least one leaf spot disease associated with it, but the most common and well researched of the spring leaf spot diseases is Leaf Spot and Melting Out of Kentucky Bluegrass, so it gets the most attention here.

Symptoms and Signs

The causal fungi initially penetrate and infect leaf tissues producing small brown spots. These spots on infected leaves expand and develop dark purplish or reddish-brown oval borders with tan centers. The spots are often described as “football” shaped (Photo 1). Infected leaves yellow as the disease progresses and senesce prematurely. This process can thin turf stands, but most modern turfgrass varieties can tolerate minor infections and the loss of a few leaves, so the thinning is generally minimal (Photo 2).

Photo 1: “Football” shaped leaf lesions on Kentucky bluegrass caused by Drechslera poae. Photo: Sabrina Tirpak, Rutgers PDL

Under ideal conditions for disease development, or with very susceptible cultivars, the crowns and roots of infected plants also become diseased, which results in a brown or black rot of the crown tissue. Once the crown becomes dysfunctional, individual plants begin to fail as temperatures rise and the evapotranspiration demand on the grass increases into the summer months. This usually results in severe thinning of the turf stand and is known as the “melting-out” phase of the disease (Photo 4).

Photo 2: Yellowing and thinning Kentucky bluegrass by Drechslera poae. Photo: Richard J. Buckley, Rutgers PDL

Conidia (asexual spores) produced by the these fungi grow on stalks (conidiophores), are olivaceous (dark), and are shaped like cigars (Photo 3). They are only visible with the aid of a microscope or a high-magnification hand-lens. Trained diagnosticians can determine the genus and species of each leaf spot fungus based on spore germination characteristics as well as the size and shape of the spores.

Photo 3: Conidia of Drechslera siccans on a conidiophore. Photo: Richard J. Buckley, Rutgers PDL

Disease Cycle

The causal fungus of Leaf Spot and Melting Out of Kentucky Bluegrass, Drechslera poae, survives the winter in crowns and roots of infected turfgrass plants and/or on turf debris (thatch). This fungus begins to grow and reproduce during cool, wet weather in late-winter and early-spring beginning in March. Conidia produced by the fungus are splashed by rain or irrigation water to newly emerging grass leaves causing leaf spots. Successive generations of spores and leaf spot symptoms are produced during mid-to-late spring with the highest concentrations of conidia found on leaf litter during May at temperatures between 50 and 65^oF. Research suggests that conidial production ceases at temperatures over 68^oF. If conditions are favorable for disease development in late-spring, infections of the crowns result in the melting-out phase of the disease by summer. Melting-out causes large areas of previously thinning turfgrass to fail.

Be aware that not all of these closely related pathogens follow the same disease-cycle. Differences among the various causal fungi are generally related to host and the temperature range necessary for disease activity. Table 1. outlines the group.

Disease	Typical Host	Pathogen	Environment
Leaf Spot and Melting Out	Kentucky bluegrass	Drechslera poae	Cool, wet weather in spring
Net Blotch	Fescues	Drechslera dictyoides	Cool, wet weather of late-spring
Brown Blight	Perennial ryegrass	Drechlsera siccans	Cool, wet weather of spring and fall
Red Leaf Spot	Bentgrass	Drechslera erythrospila	Warm, wet weather of summer
Melting Out	All cool-season grass	Bipolaris sorokiniana	Warm, wet weather of summer
Fading Out	All cool-season grass	Curvularia spp.	Warm, wet weather of summer

Cultural Conditions that Favor Disease

Cultural conditions favoring leaf spot disease include: mowing at low cutting heights, light and frequent irrigation cycles, and excessive nitrogen fertilizer applications in early spring. These diseases can also be severe on turfgrasses with nitrogen deficiencies. There is evidence that turf stands (KBG) with excessive thatch accumulations can have more severe disease outcomes. Although many improved cultivars of Kentucky bluegrass and perennial ryegrass have a high degree of leaf spot resistance, other older cultivars—often found in inexpensive seed mixtures or as components in tall fescue sod—are susceptible (Photo 4). These cultivars can sustain severe damage and will suffer recurring disease outbreaks in a single season and over multiple years.

Management

Genetics is everything with leaf spot diseases. The single, most effective cultural practice for preventing severe damage is to plant leaf spot-resistant turfgrass cultivars whenever possible. Lists of leaf spot-resistant grasses can be found on the National Turfgrass Evaluation Program website (NTEP.org). Another important cultural practice is to apply only moderate amounts of nitrogen fertilizer at a time (0.5 lb. nitrogen/1,000 sq. ft.), particularly in the early spring. If higher rates are necessary, using products that are formulated with at least 50% of the available nitrogen in a slow release form are desired to avoid succulent and over-stimulated foliage. Mowing lawns at cutting heights above 2.5 inches during spring may help to reduce the severity of leaf spot and melting-out. If irrigation is required, watering inputs should be made to prevent drought stress and sustain growth, without creating an overly wet canopy. Thatch accumulations should be mechanically removed.

Photo 4: Melting out of Kentucky bluegrass due to Drechslera poae. Note the damage to the older cultivar compared to the improved cultivar. Photo: unknown

Chemical Control

Many fungicides are labeled and efficacious for the control of leaf spot diseases. Timing matters for disease outcomes and preventative fungicide applications provide the best results. Make applications to susceptible grasses in April at the first evidence of leaf infection. Products containing iprodione, chlorothalonil, mancozeb, fluazinam, fludioxonil, azoxystrobin, or penthiopyrad have demonstrated good control of leaf spot diseases in University Trials. Be aware that some research trials have shown enhanced leaf spot disease activity with thiophanate-methyl products, even though they are labeled for leaf spot control. For a complete list of labeled materials and their efficacy, see University of Kentucky’s information bulletin:

Chemical Control of Turfgrass Diseases 2020. Bruce B. Clarke, Department of Plant Biology, Rutgers University; Paul Vincelli, Department of Plant Pathology, University of Kentucky; Paul Koch, Department of Plant Pathology, University of Wisconsin-Madison; Gregg Munshaw, Department of Plant and Soil Sciences, University of Kentucky.

Filed Under: Landscape, Nursery, & Turf, Plant Diagnostic Lab, Turf

December 22, 2021 Richard Buckley

Beech Leaf Disease in New Jersey

A new disease of beech trees (Fagus spp.) called ‘Beech leaf disease’ (BLD) has increasingly been observed in landscaped and forested areas in the Northeastern USA and Canada. The disease was first reported on American beech, Fagus grandifolia, in Lake County Ohio in 2012, and has spread to Pennsylvania, New York, Ontario (Canada), Connecticut, Maine, Massachusetts, Rhode Island, New Jersey, West Virginia and Virginia. In New Jersey, the disease was first reported in 2020 and has been confirmed in 10 counties including: Bergen, Essex, Hunterdon, Mercer, Monmouth, Morris, Passaic, Somerset, Sussex, and Union.

New Jersey Beech Leaf Disease Detection Map

BLD primarily affects American beech, F. grandifolia, however, it has also been observed on European beech, F. sylvatica; Oriental beech, F. orientalis; and Chinese beech, F. engleriana. All of the specimens seen in the Rutgers Plant Diagnostic Lab have been American beech.

A foliar nematode species has been isolated from beech leaves and buds. This nematode was initially identified as Litylenchus crenatae subspecies crenatae, a species described in Japan on Fagus crenata that does not cause disease. In 2020, the cause of BLD was proven to be a newly described foliar nematode, Litylenchus crenatae subsp. mccannii, which is closely related to L. crenatae subsp. crenatae. L. crenatae subsp. crenatae has not been found on ornamental plantings of American beech in Japan. Conversely, L. crenatae subsp. mccannii has not been found on ornamental plantings of Japanese beech in North America. While the origin of L. crenatae subsp. mccannii and its native distribution are not clear, all other known species of nematode in the genus Litylenchus are found in the Pacific Rim.

Litylenchus crenatae subsp. mccannii isolated from beech leaf tissues in the Rutgers Plant Diagnostic Laboratory. Photo: Sabrina Tirpak, Rutgers PDL

In 2019, research scientists at the USDA took nematodes from diseased trees and inoculated them onto the buds of young, healthy trees in a greenhouse, waited for symptoms to appear, then re-isolated the nematode from the affected leaves. This process is called Koch’s postulate’s, which is plant pathology’s gold standard for verifying the cause of a disease.

Despite these findings, some researchers question the role of the nematode as the only cause of BLD. Recent reports suggest that diseased beech leaves also contained a fungus and 4 species of bacteria that are also carried by the nematode. This research suggests that both the nematode and a pathogen that it carries may be contributing to the disease. The original research from the USDA, however, suggests that nematode feeding alone can cause the disease.

The BLD nematode predominantly overwinters in buds. The nematode migrates from leaves to the buds beginning in August. After bud-break in the spring, the nematodes cannot be found in symptomatic leaf tissue until late-June or early-July. DNA-based markers, however, can confirm the presence of the nematode, presumably due to eggs, in these leaves. By early summer, the nematodes appear in the leaves and are easily identified in a laboratory setting. The numbers of nematodes in the infected leaves increase through fall. It is assumed that some nematodes overwinter in leaves on the ground. The mechanisms of transmission and spread within trees, among trees, and from site to site, are unknown. Research is ongoing in the hopes of answering these questions.

The initial symptoms of BLD include dark-green striped bands between the veins of leaves. The dark-green bands are easily seen by holding leaves up to the light and/or looking up into the canopy. In many cases, the size of the affected leaves is reduced. The banded areas usually become leathery-like, and leaf distortions–curling and crinkling–are often observed. These symptoms are best seen by looking down on the top of the leaf.

As seen from below, dark-green striping is clearly evident between the leaf veins. Photo: Jerry Giordano, Cornell Cooperative Extension

As seen from above, affected leaves are smaller, leathery, and distorted. Photo: Jerry Giordano, Cornell Cooperative Extension

Affected leaves thicken and may yellow between the veins. Photo: Sabrina Tirpak, Rutgers PDL

As symptoms progress, aborted buds, reduced leaf production, and premature leaf drop lead to an overall reduction in canopy cover. This ultimately results in the death of saplings within 2-5 years of infection and of large trees within 6 years. In areas where the disease is established, the proportion of symptomatic trees can reach more than 90%. There is significant concern that this disease will dramatically reduce the numbers of beech and their ecological services in Northeastern forests.

Because the research on BLD etiology is ongoing, and questions regarding dissemination and spread remain unanswered, management and control options are limited. Several pesticide options are currently being investigated including: abamectin, emamectin benzoate, and potassium-phosphite as potential controls. The avermectin materials are known to be effective nematicides in other animal and plant systems and may eventually be determined to be efficacious for this disease. At this time, however, the efficacy of any of these materials is unknown and are not currently recommended as treatments. Be aware that much more work needs to be done to understand this new disease before effective treatment protocols can be discussed.

In general, the spread of invasive species can be prevented by restricting the movement of plant materials and monitoring trees closely for signs and symptoms. BLD has spread very quickly eastward in the United States and is concerning to all of us. The Rutgers Plant Diagnostic Laboratory and our partners at the New Jersey Division of Community Forestry are interested in tracking this disease within New Jersey. Please contact the lab if you suspect a problem. Samples can be evaluated free of charge for the 2022 growing season.

Filed Under: Landscape, Nursery, & Turf, Plant Diagnostic Lab Tagged With: Beech, Foliar nematode

July 12, 2016 Richard Buckley

Answers to Emerald Ash Borer Questions

The NJ Emerald Ash Borer Task Force has agreed upon the following in response to EAB management questions in NJ:

All ash trees in NJ should be considered at high risk for EAB.
It is appropriate to begin treatment of high value ash trees throughout NJ now.
For any questions about treatment methods, we should refer to the “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer” bulletin on the website (emeraldashborer.nj.gov).
We should recommend that people work with a Certified (Licensed) Tree Expert or Approved Consulting Forester to help them determine whether or not their ash trees are good candidates for a treatment program (vs. removal), and that they should contract a Certified Pesticide Applicator to complete any chemical treatments.
Any trees determined to be of high safety risk should be removed immediately.
Any actively infested trees should be cut down and chipped as soon as possible and then left on site (in the municipality).
For all other ash, it is best to complete removals in the fall and winter. The material must be processed (chipped or de-barked) before emergence (by late April).
For municipalities, we should recommend triage of the ash resource to spread out ash removals over several years.

Rich Buckley at the Rutgers Plant Diagnostic Lab has agreed to examine samples for EAB at no charge as long as they are brought to the lab.

Anyone interested should be directed to contact the Rutgers Plant Diagnostic Lab, and should bring the beetle, larvae, or sample of symptomatic tissue (chunk of bark with exit wound).

The NJ EAB Task Force is comprised of representatives from the NJ Department of Agriculture, NJ State Forest Service, USDA APHIS, Rutgers University, and the US Forest Service. The Task Force works to collaborate on EAB management decisions and advice, and to consolidate and disburse information and resources relevant to EAB in New Jersey.

Filed Under: Landscape, Nursery, & Turf, Plant Diagnostic Lab

May 13, 2016 Richard Buckley

Ladies and Gentlemen: Start Your Engines!

In February, I was scheduled to speak at a landscape program in Rockville, MD. Before I went on, I had a chance to chat with one of the other speakers–the esteemed entomologist from the University of Maryland, Dr. Mike Raupp–who said concerning the Emerald Ash Borer, “nobody believes you until the trees start dying.”

Thin-canopied ash trees in a central-Jersey landscape. Photo: Richard Buckley, Rutgers PDL