As a result of all the rain we’ve been having in Arkansas recently, we have seen a high incidence of peach bacterial spot, caused by the bacterium Xanthomonas arboricola pv. pruni. This pathogen primarily infects the fruit, leaves, and twigs of peach trees, leading to significant economic losses in commercial orchards and reduced yields in home gardens. Spread of peach bacterial spot is facilitated by moisture, making this disease particularly prevalent in areas with warm, wet springs.
Symptoms of bacterial spot typically appear in the spring and early summer. On leaves, the disease manifests as small, water-soaked lesions that can turn dark brown or black, often with a red/pink or yellow halo. This spring, we have been seeing a lot of lesions with the red/pink halo. While individual lesions are restricted by leaf veins, lesions can coalesce and become discolored areas that seem to cross the leaf vein . Leaves may become chlorotic, causing premature defoliation. Additionally, the centers of the leaf lesions may drop out, resulting in a shot-hole look to the leaves . Be aware that a fungal pathogen (Wilsonomyces carpophilus) can also cause shot-hole type symptoms on peach leaves, so symptoms alone are not diagnostic. Bacterial spot lesions may be most present where water tends to run or pool on peach leaves, specifically along the midrib and at the tip. On fruit, small, dark, pitted spots develop, sometimes surrounded by a yellow halo on more mature fruit. These spots can make the fruit unmarketable even though the internal flesh is usually unaffected. Twig lesions and cankers can lead to dieback and further reduce tree vigor.
The bacterium overwinters in twig cankers and buds and is spread by rain splash, wind, and contaminated tools. Once conditions become favorable—typically during warm, humid weather—the bacteria multiply rapidly and infect new tissue through natural openings or wounds. Effective management of peach bacterial spot involves an integrated approach, including the use of resistant cultivars and proper pruning to improve air circulation. Cultural practices play a vital role in managing the disease. Sanitation—such as removing infected plant debris—and avoiding overhead irrigation can help reduce disease spread. Additionally, monitoring weather conditions and using predictive models can guide timely interventions. Although peach bacterial spot cannot be completely eradicated once established, diligent management can significantly minimize its impact.
There are no chemical recommendations for homeowners and other non-commercial growers in Arkansas. Different states have different chemicals allowed for use and have potentially different rules on how they can be applied, so those growing peaches outside of Arkansas should review proper chemical treatments for their state. In Arkansas, commercial growers should use oxytetracycline sprays (e.g., Mycoshield) during high-risk periods and preventative sprays with copper-based bactericides. Obtaining good coverage with the sprays is extremely important! Prevention of this disease needs to start before symptoms appear. Copper applications should start in the dormant to early budbreak stages . Rates are different for every growth stage, decreasing as time goes on. Careful application timing and proper concentrations of the copper-based bactericides are very important, as copper can be phytotoxic to peaches. For details on application rates and timing for all peach diseases in commercial orchards in Arkansas , please see page 71-75 of the 2025 Arkansas Plant Disease Control Products Guide or the 2025 Southeastern Peach, Nectarine, and Plum Pest Management and Culture Guide which covers management guidelines for several southeastern states, including Arkansas.
Bacterial Spot Symptoms on Peach Leaves (Brown/black lesions and leaf chlorosis)
Photo by U. Mazzucchi, Università di Bologna, Bugwood.org
Bacterial Spot Symptoms on Peach Leaves (Red halo)
Photo by Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Bacterial Spot Symptoms on Peach Fruit (Brown lesions with yellow halo)
Photo by Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org
Xanthomonas arboricola pv. pruni Streaming out of Peach Leaf (10X Magnification)
Photo by Jason Pavel, University of Arkansas Cooperative Extension Service
Fire Blight
Fire blight is another bacterial plant disease that we have been seeing frequently in the clinic, likely thanks to our extremely wet weather. Fire blight is a significant bacterial disease caused by Erwinia amylovora, primarily affecting members of the rose family (Rosaceae), especially apples, pears, and related ornamental plants such as crabapples and hawthorns. The disease gets its name from the scorched appearance of infected plant tissue, which looks as though it has been burned by fire. It is most damaging in warm, humid conditions, especially during bloom when the bacteria can enter through the flowers.
The first signs of fire blight typically appear in the spring during or shortly after bloom. Blossoms wilt and turn brown or black. Infected shoots may curl into a characteristic “shepherd’s crook” shape. As the disease progresses, it can spread into branches and even the main trunk, forming sunken, oozing cankers that can girdle and kill the affected areas. Leaves will turn brown/black, particularly along the midrib and starting from the petiole side of the leaf. The bacteria overwinter in twigs or branches, and insects and rain help disperse the bacteria during the spring. Note that since the bacteria causing fire blight often infect through individual blooms, you can have healthy blossom clusters right next to infected blossom clusters.
Fire blight spreads rapidly under the right conditions, making timely management critical. Cultural control is essential: this includes pruning out infected wood at least 10–12 inches below visible symptoms during dry weather and disinfecting tools with fresh 10% bleach in between cuts to avoid spreading the pathogen. Avoiding high-nitrogen fertilization can help, as lush, fast-growing shoots are more susceptible to infection. In terms of chemical control, Arkansans can refer to MP154, the 2025 Arkansas Plant Disease Control Guide. (Homeowners of fruit trees can refer to page 79 on fire blight. Homeowners of ornamental trees can refer to page 115 on bacterial leaf spots/blights. Commercial growers of apples can refer to pages 63-67. Commercial growers of pears can refer to pages 70 and 71, and commercial growers of ornamentals can refer to page 81.)
Long-term management strategies include planting fire blight-resistant cultivars and ensuring good air circulation through proper spacing and pruning. Fire blight is difficult to eliminate once established, so prevention and early intervention are key. In regions where the disease is common, a combination of cultural, chemical, and horticultural practices offers the best chance of reducing its impact.
Characteristic "Shepherd's Crook" Symptom of Fire Blight on Pear
Photo by Edward Sikora, Auburn University, Bugwood.org
Pear Branch with Dead Leaves and Canker Caused by Fire Blight
Photo by Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org
Erwinia amylovora Oozing out of and Spreading down a Pear Leaf Midrib
Photo by John Hartman, University of Kentucky, Bugwood.org
Erwinia amylovora Streaming
out of an Apple Section under the Compound Microscope
Photo by Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org
Erwinia amylovora, the Causal Agent of Fire Blight
Photo by Bacheline Joseph, University of Florida, Bugwood.org
Crape Myrtle: Crape Myrtle Bark Scale (CMBS)
The question asked most often through Arkansas Extension's Ask the Arkansas Pest Crew service is about crape myrtles with white spots or scabs and/or black bark . These white spots are an invasive insect pest known as crape myrtle bark scale (CMBS), Acanthococcus lagerstroemiae, and the blackening of the bark is a superficial side effect of CMBS feeding. CMBS is originally from Asia that has become a significant problem in the southeastern and southern United States. It specifically targets crape myrtles (Lagerstroemia spp.), popular ornamental trees known for their vibrant flowers and smooth, mottled bark. Since its first detection in the U.S. in Texas around 2004, the pest has steadily spread, weakening trees and diminishing their ornamental value.
The most visible sign of CMBS infestation is the presence of small, white to gray, felt-like bumps clustered on the bark, especially on trunks and in protected branch crotches. These are the protective coverings of the scale insects. When crushed, the scales exude a pinkish fluid, a helpful diagnostic feature. Affected trees often exhibit heavy black sooty mold on the bark and leaves—this mold grows on the honeydew (a sugary excretion) produced by the scale insects. While sooty mold doesn’t harm the tree directly, it can block sunlight from reaching leaves and make the plant look unsightly.
CMBS can stress trees by feeding on their sap, which may lead to reduced vigor, poor blooming, dieback, and increased susceptibility to other pests and diseases. Although healthy crape myrtles typically survive infestations, the aesthetic damage and decline in plant health are cause for concern. Management of this pest includes physical, cultural, and chemical approaches. Pruning out and destroying heavily infested branches and washing the bark with a stiff brush and water can help reduce populations. Introducing beneficial insects like lady beetles, which feed on CMBS, supports natural biological control.
For more severe infestations, systemic insecticides such as those containing imidacloprid or dinotefuran can be effective when applied in the spring. However, chemical use should be timed carefully to avoid harming pollinators and should be integrated with non-chemical methods. Additionally, a dormant horticultural oil can be applied after leaf fall; obtaining good coverage on the trunk and branches is extremely important. For more information about chemical control and the scale insect’s life cycle, please see Dr. Jon Zawislak’s detailed article.
To slow the spread of CMBS, one should share what they know about early detection and remind people of the importance of not transporting infested plant material. Often, the first detail people notice is the blackening bark. Keeping an eye out for blackening bark and checking periodically for the white CMBS on the wood can catch the problem early and reduce the spread of the pest. Make sure to check for evidence of CMBS before purchasing a crape myrtle. Pruned twigs and branches that may have CMBS should be immediately burned on-site or double bagged and disposed of. Keeping these measures in mind can help reduce or prevent CMBS becoming a problem in your yard or nursery.
CMBS on Crape Myrtle Branch
Photo by Jim Robbins, University of Arkansas CES, Bugwood.org
CMBS Females
Photo by Gary Brooks, Bayer CropScience, Bugwood.org
CMBS on Crape Myrtle Branch
Photo by Jim Robbins, University of Arkansas CES, Bugwood.org
Flowers from a Healthy Crape Myrtle (top row) Compared to Flowers from a Crape Myrtle Infested with CMBS (bottom row)
Photo by Jim Robbins, University of Arkansas CES, 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.
Arkansas Plant Health Clinic | 2601 N. Young Avenue | Fayetteville, AR 72204 US
