Issue 7, August 28, 2025

Taylor Klass, Lead Diagnostician

Jason Pavel, Diagnostician

Blackberry anthracnose, caused by the fungus Elsinoe necator (formerly Elsinoë veneta), is a common and damaging disease of blackberries. The pathogen can infect canes, leaves, and fruit, but cane lesions are the most destructive, leading to reduced vigor, lower yields, and shortened plant lifespan. The fungus overwinters in infected canes and produces spores during wet spring weather. Due to the abundance of wet weather this spring and early summer, there have been ample opportunities for spore production this year. The spores spread to young, actively growing tissues, meaning the new plant growth in spring is especially vulnerable.

The first symptoms typically appear in late spring as small, purplish, sunken spots on new canes. These lesions (called pit lesions) expand into larger, gray centers with raised, dark-purple margins that give them a “scabby” appearance. When numerous, they can girdle canes, weakening or killing them. In severe cases, affected canes may crack, dry out, and die back. Leaves can also be infected, showing small purple spots that turn white in the center as they enlarge. The centers of the lesions may fall out, resulting in a “shot-hole” appearance. Infected fruit display drupelets that are uncharacteristically small and shriveled. Overall, leaf and fruit symptoms are generally less impactful than cane lesions. The damage from anthracnose becomes most noticeable by midsummer, when weakened canes fail to support normal fruiting.

At this time of year (late summer and early fall), additional cane lesions may form superficially on the surface of blackberry canes. These lesions are gray in color and can make it look like the blackberry has gray bark. While still important, these later season cane lesions are not as damaging as the early season pit lesions.

If you have had issues with blackberry anthracnose during this growing season, there are steps that you can take post-harvest and during the winter to reduce the fungal inoculum and the chance of recurrence next spring. Removing and destroying infected floricanes after harvest reduces the amount of overwintering inoculum. A fungicide can then be applied after removing infected floricanes (see page 56 of the 2025 Arkansas Plant Disease Control Products Guide for specific product recommendations for commercial growers). During the winter, prune out and destroy any primocanes or remaining floricanes that are infected with anthracnose. Additionally, commercial growers can use a delayed dormant application of lime sulfur. Cultural control should include pruning and wide row spacing; these controls ensure good airflow, which helps plants dry faster, lowering disease pressure. Planting resistant or tolerant cultivars, when available, is an effective long-term strategy. During the early spring, when new growth is emerging and conditions are wet, commercial growers can apply fungicides to mitigate new infections of fresh growth (see page 56 of the 2025 Arkansas Plant Disease Control Products Guide for specific product recommendations for commercial growers). In backyard or small-scale plantings, cultural practices such as sanitation and pruning are often sufficient to keep the disease at manageable levels. For more information on blackberry anthracnose in Arkansas and specifically fall and winter management of the disease, please see this Arkansas Blackberry Factsheet by Sherri Sanders and Dr. Terrence Kirkpatrick and the Arkansas Fruit, Vegetable, and Nut Update by Dr. Aaron Cato.

Cane Pit Lesions caused by Anthracnose

Photo by Charles Drake, Virginia Polytechnic Institute and State University, Bugwood.org

Cane Pit Lesions caused by Anthracnose

Photo by Penn State Department of Plant Pathology & Environmental Microbiology Archives, Penn State University, Bugwood.org

Anthracnose Symptoms on Blackberry Fruit

Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service

Bacterial leaf scorch (BLS), caused by Xylella fastidiosa, is a long-term, often fatal disease of many landscape trees in Arkansas and across the country. The bacterium lives inside a tree's vascular system (specifically the xylem), blocking the flow of water and nutrients and gradually stressing the tree. Symptoms typically develop in midsummer through late summer, when hot and dry conditions make the effects more obvious. Leaves first show a marginal scorch — tissue browning that starts at the edges and moves inward — with a narrow yellow or reddish border separating the dead and healthy tissue. We tend to see a lot of environmental/drought scorch on tree leaves at this time of year (late summer and early fall). One key feature that helps distinguish BLS from simple drought scorch is that symptoms tend to reappear year after year on the same branches or sections of the canopy, whereas environmental scorch is usually more arbitrary and varies with weather conditions. Environmental scorch tends to evenly impact a good portion of the tree canopy, while symptoms of BLS are randomly scattered in specific canopy sections. BLS causes lower branches and older leaves on those branches to typically brown first while environmental scorch symptoms will first appear on the younger leaves on the branch tips and at the top of the tree. Additionally, environmental scorch does not generally have the yellow border between brown and green tissue that is characteristic of BLS.

This disease affects a wide range of tree species, including, but not limited to, oak (especially red and pin oaks), sycamore, elm, maple, sweetgum, ginkgo, and mulberry. Once established, the bacterium spreads through the xylem and cannot be eradicated (it is systemic). It is moved from tree to tree primarily by leafhoppers, treehoppers, and spittlebugs that feed on xylem sap. Infected trees often leaf out normally in spring but decline during summer, with affected branches gradually thinning and dying back over several years. There is currently no cure, but management practices that reduce stress — such as watering during drought, mulching, and avoiding over-pruning or heavy nitrogen fertilization — can help prolong the life of an infected tree. Severely affected or hazardous trees may eventually need to be removed.

Bacterial Leaf Scorch (BLS) Symptoms

Photo by Brian Olson, Oklahoma State University, Bugwood.org

BLS Symptoms on a Ginkgo Leaf

Photo by Sherrie Smith, University of Arkansas Cooperative Extension

BLS Symptoms on a Tree

Photo by John Hartman, University of Kentucky, Bugwood.org

BLS Symptoms on Leaves

Photo by Sandra Jensen, Cornell University, Bugwood.org

BLS Symptoms on Leaves

Photo by Sandra Jensen, Cornell University, Bugwood.org

BLS Symptoms on a Tree

Photo by Edward L. Barnard, Florida Department of Agriculture and Consumer Services, Bugwood.org

Oak tubakia leaf spot, caused by the fungus Tubakia dryina, is one of the most common late-season leaf spot diseases of oaks. Oaks in the red oak group are especially susceptible, though white oaks and other species can also show symptoms under favorable conditions. The disease typically becomes noticeable in mid-to-late summer, when dark brown spots and blotches begin to appear on leaves. Unlike some springtime leaf diseases, tubakia leaf spot tends to show up after the hottest part of summer, often giving the impression of drought or heat stress to the untrained eye.

Symptoms usually start as small, circular to irregular brown spots (¼ – ½ inch diameter) that may enlarge and merge into large necrotic areas. The spots are often surrounded by a yellow halo, and they can develop along leaf veins or margins as the season progresses. In heavily affected trees, especially during the late summer and early fall, the disease can cause premature leaf drop, which can be alarming to homeowners. However, since symptoms develop late in the growing season, after most of the tree’s energy reserves have been produced, the disease rarely causes long-term damage or tree death.

The fungus survives in fallen leaves and twigs, releasing spores during wet weather in the spring. The spores will infect the oaks in the spring, but symptoms may not show up until late summer. Management is usually not necessary in established trees, as the disease is considered primarily an aesthetic issue. For young or stressed oaks in landscapes, good cultural practices can help reduce disease impact — including raking and removing fallen leaves in autumn to lower inoculum, watering during drought to reduce stress, and avoiding unnecessary wounding or construction damage to roots. Fungicide applications are rarely recommended, since infection occurs earlier in the season and symptoms don’t show up until much later.

Oak tubakia leaf spot is often confused with other late-season oak problems, but there are some useful distinctions. Tubakia usually appears in mid-to-late summer, showing up as dark brown to black spots or blotches, sometimes with yellow halos. The spots may be scattered or clustered, and entire leaves can brown and drop early if infections are heavy. By contrast, oak anthracnose (caused by Apiognomonia quercina) typically shows up much earlier in the season, often in spring, and is closely tied to cool, wet weather. Anthracnose lesions tend to follow the leaf veins, causing irregular blotches, distorted leaves, and sometimes twig dieback — patterns less common with tubakia leaf spot.

Bacterial leaf scorch (BLS), caused by Xylella fastidiosa, can also be mistaken for tubakia leaf spot because it appears in summer and causes browning. Unlike  the scattered leaf spots caused by Tubakia, BLS scorch is more uniform along leaf margins and recurs year after year on the same branches, gradually expanding as the tree declines. Tubakia leaf spot, in contrast, is not systemic; it causes cosmetic spotting and leaf drop late in the season but does not lead to progressive branch dieback. BLS also produces a distinct band of yellow or reddish tissue separating the scorched (brown) edge of the leaf from the still-green interior while tubakia leaf spot doesn't as reliably produce a yellow border between green and brown tissue.

Tubakia Leaf Spot Symptoms

on an Oak Leaf

Photo by Bruce Watt, University of Maine, Bugwood.org

Close-up of Tubakia Leaf Spot Signs (Black Fruiting Bodies) and Symptom on an Oak Leaf

Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service

Tubakia Leaf Spot Fruiting Bodies (Pycnothyria) and Asexual Spores (Conidia)

Photo by Bruce Watt, University of Maine, Bugwood.org

Tubakia Leaf Spot Symptoms

on Oak Leaves

Photo by Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org

Tubakia Leaf Spot Symptoms on an Oak Leaf

Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service

For lawns affected by large patch disease, the recommended window for fall fungicide applications is approaching. A treatment made between September 20 and October 10 will help suppress the disease and protect turf as it enters cooler weather. Applying fungicides during this period (the period when the fungus is active) is an important step in reducing disease severity and promoting healthier turf next spring. For treatment, landscapers or commercial applicators can use Headway (propiconazole+azoxystrobin), Tourney (metconazole), Trinity (triticonazole), Triton (triticonazole), Pedigree (flutolanil), or Lexicon (fluxapyroxad + pyraclostrobin). These products are labeled for both home lawns and golf courses. Homeowners may use 'Spectracide Immunox Fungus Plus Insect Control for Lawns', 'Scotts Lawn Fungus Control', 'Scotts Disease EX Lawn Fungicide', or 'Bonide Infuse Systemic Disease Control Lawn and Landscape'. Follow all label directions.

Symptoms of Large Patch in Turf

Photo by Matthew Zidek, Texas A&M Agrilife Extension Service, Bugwood.org

This bulletin from the Cooperative Extension Plant Health Clinic (Plant Disease Clinic) is an electronic update about diseases and other problems observed in our lab each month. Input from everybody interested in plants is welcome and appreciated.

TAYLOR KLASS is a plant pathologist /instructor and JASON PAVEL is a plant pathologist, both with the University of Arkansas System Division of Agriculture. They are located at the Plant Health Clinic, 2601 N. Young

Avenue, Fayetteville, Arkansas.

Acknowledgements: Gratitude is due to Sherrie Smith, the originator of the Plant Health Clinic newsletters. Her works are a vital source of reference for the information provided herein.

"This work is supported by the Crop Protection and Pest Management Program [grant no. 2017-70006- 27279/project accession no. 1013890] from the USDA National Institute of Food and Agriculture."

University of Arkansas, United States Department of Agriculture and County Governments Cooperating

Pursuant to 7 CFR § 15.3, the University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services (including employment) without regard to race, color, sex, national origin, religion, age, disability, marital or veteran status, genetic information, sexual preference, pregnancy, or any other legally protected status and is an equal opportunity institution.