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Rose: Powdery Mildew
Powdery mildew is a common fungal disease that affects roses and many other ornamental plants. It appears as a white, powdery coating on the leaves, stems, and sometimes flower buds. On roses, it is caused by the fungus Podosphaera pannosa. The fungus thrives in moderate temperatures (60–80°F) and high humidity, especially in shaded or poorly ventilated areas. Despite thriving in high humidity, it, unlike many other fungal pathogens, does not require free water to infect plants. In addition to stealing nutrients from roses, the powdery mildew fungus can also impede leaf photosynthesis by blocking the leaves from accessing the sunlight.
Early symptoms of powdery mildew on roses often start with distorted or curling young leaves and shoot tips. As the disease progresses, the characteristic white, talcum-like spores become visible on both sides of the leaves and on tender stems. Severe infections can stunt growth, reduce flowering, and cause premature leaf drop, ultimately weakening the plant.
Remember that even though rose powdery mildew sounds very similar to rose downy mildew, they are two different diseases caused by different types of pathogens. As a result, control for these diseases is different. Briefly, rose downy mildew causes yellow, angular spots on the tops of rose leaves, but only forms its fuzz (more gray-colored than powdery mildew) on the underside of leaves. While downy mildew also loves humidity, it needs water to infect rose leaves (in contrast to powdery mildew). If you are unsure whether your rose is suffering from powdery or downy mildew, feel free to consult with your local extension agent or submit physical and/or image samples to the clinic.
Cultural control is one of the best ways to manage powdery mildew on roses. This includes planting resistant rose varieties (climbers, ramblers, and hybrid teas are susceptible), ensuring good air circulation by proper pruning and spacing, and avoiding overhead irrigation that might contribute to humidity buildup. Collect and remove any leaves that have fallen, as they can serve as an inoculum source for future infection.
If the infection is significant, fungicides labeled for powdery mildew may be used as a preventative or curative measure. These should be rotated to avoid resistance buildup. Examples of fungicides labeled for powdery mildew in Arkansas currently include Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens; BioAdvanced Disease Control for Roses, Flowers & Shrubs or BioAdvanced All-In-One Rose & Flower Care; Ortho Garden Disease Control or Ortho
Rose & Flower Disease Control; Bonide Sulfur Plant Fungicide (labeled for organic use) or Bonide Mancozeb Flowable with Zinc Concentrate. GreenCure Fungicide, Kaligreen, MilStop SP, and Actinovate Lawn & Garden Biological Fungicide are other options labeled for organic use. Always follow the directions on the product labels.
Regular monitoring, early detection, and proper cultural practices are key to keeping powdery mildew in check and maintaining the health and beauty of rose plants.
Powdery Mildew on Rose Leaves
Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service
Powdery Mildew on Rose
Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service
Spores of Powdery Mildew, 40x Magnification
(Note that this powder mildew was on mint, so it is a different species of pathogen)
Photo by Jason Pavel, University of Arkansas Cooperative Extension Service
Rose: Rose Rosette Virus
Rose rosette virus (RRV) is a serious and incurable disease affecting rose plants, particularly the multiflora rose (Rosa multiflora) and many cultivated garden roses. It is caused by a virus in the Emaravirus group and is spread by a tiny eriophyid mite (Phyllocoptes fructiphilus), which is carried by wind or transferred between plants through contact. These mites are microscopic, only a quarter of the size of a spider mite, and cannot be seen without some type of magnification. Once a rose is infected, the disease is systemic and currently has no cure.
Symptoms of rose rosette can vary depending on the rose cultivar and the stage of infection but typically include excessive thorniness, abnormal or "witches’ broom" growth (dense clusters of deformed shoots), elongated and reddened stems, distorted leaves, shortened internodes, reduced winter hardiness, and a lack of normal flowering or abnormal flower color. Buds may remain closed or produce deformed blooms. These symptoms can sometimes be confused with herbicide damage, but RRV symptoms are progressive and eventually lead to the decline and death of the plant. It is important to note that roses can remain asymptomatic for several months after RRV infection, meaning that the virus can be transmitted to your rose months before you start noticing symptoms.
Management of rose rosette virus focuses on prevention and early detection. Since there is no effective treatment once a plant is infected, the best approach is to remove and destroy infected plants promptly (including their root systems) to reduce the spread of the virus and its mite vector. Double bag and dispose of or immediately burn the infected plant. To prevent the potential spread of infected mites, don’t transport the infected plant material through the yard or elsewhere without enclosing it in a bag or other container. After plant removal, be sure to sterilize any tools or equipment used to cut up or dig up the plant material.
Controlling the mite population is also essential—this can be done by minimizing dense plantings and avoiding overhead irrigation that might encourage mite movement. Additionally, miticides labeled for use on eriophyid mites, such as Avid (abamectin) or horticultural oil, can help in preventing and controlling the vector population. Vigilant monitoring and rapid removal of symptomatic plants are critical.
Home gardeners and commercial growers alike should be aware of RRV and act quickly if symptoms appear, as the disease can spread rapidly through rose plantings and have a significant impact on the landscape.
Excessive Thorniness on a Rose Infected with RRV
Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service
Elongated and Red Stems of Rose Infected with RRV
Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service
Phyllocoptes fructiphilus, the Tiny Eriophyid Mite that Transmits RRV
Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service
Strawberry: Anthracnose Crown Rot
Anthracnose crown rot is a damaging disease of strawberry plants caused by several species of the fungus Colletotrichum. It affects the crown, which is the central growing point of the plant, and can lead to rapid plant collapse and significant yield losses. Anthracnose crown rot can also cause lesions on strawberry stolons and petioles. The disease is most common in warm, wet conditions where susceptible cultivars are grown.
Infected strawberry plants may initially show symptoms such as wilting during the heat of the day, stunted growth, or reddish to brown discoloration of the crown tissue when cut open. As the disease progresses, plants often collapse and die suddenly, especially during periods of stress.
Anthracnose crown rot spreads through soil, splashing water, tools, infected transplants, and human activity. The fungus can survive in plant debris and soil, making crop rotation and sanitation critical for disease management. Using disease-free transplants is one of the most effective ways to prevent introducing the pathogen into new fields. In fields with a history of the disease, it is important to avoid overwatering and to avoid applying high nitrogen rates. Planting cultivars that are more tolerant of the disease can be helpful too, although no currently available cultivars are fully resistant.
Fungicides labeled for anthracnose may help manage the disease when used as part of an integrated disease management program, but they are most effective when applied preventatively. See pages 57 - 61 of the 2025 Arkansas Plant Disease Control Products Guide for the current chemical control options in Arkansas (recommendations are different for each stage of growth that the strawberry plant is going through). Always followthe directions on the product labels. Please note that once anthracnose crown rot is established in a strawberry plant, it cannot be cured. But fungicides can still help slow disease progression.
Prompt diagnosis and removal of infected plants are essential to reducing the spread of anthracnose crown rot. Growers should regularly monitor fields for early symptoms and act quickly to protect healthy plants.
Anthracnose Crown Rot of Strawberry
Photo by Taylor Klass, University of Arkansas Cooperative Extension Service
Spores of Colletotrichum, the Causal Agent of Strawberry Anthracnose Crown Rot (40X Magnification)
Photo by Sherrie Smith, University of Arkansas Cooperative Extension Service
Strawberry: Anthracnose Fruit Rot
Strawberry anthracnose fruit rot is a significant fungal disease of strawberries caused primarily by Colletotrichum acutatum (though other Colletotrichum species may also be involved). It affects the fruit of strawberry plants and is especially problematic in warm, humid, and wet environments—conditions that favor the rapid spread and development of the disease. Anthracnose fruit rot can lead to severe yield losses in both field and high-tunnel production systems if not properly managed.
Symptoms typically begin as small, water-soaked lesions on green or ripening fruit. These lesions quickly enlarge and turn tan to dark brown or black, becoming sunken and circular. Under humid conditions, the centers of the lesions may produce masses of salmon-colored spores, which are a distinctive feature of Colletotrichum infections. Infected fruit often become soft and unmarketable, and fruit rot may continue after harvest, especially if berries were exposed to the pathogen in the field.
The disease spreads primarily through rain, overhead irrigation, and other sources of splashing water and through contaminated equipment or hands. The fungus can also be introduced through infected transplants or persist in plant debris and soil. Managing strawberry anthracnose fruit rot requires an integrated approach: using disease-free planting material, avoiding overhead irrigation, improving air circulation, and removing infected plant material promptly. Regular fungicide applications may be necessary in high-risk environments, especially during periods of wet weather, but they must be timed preventively to be most effective. As with anthracnose crown rot, see pages 57 - 61 of the 2025 Arkansas Plant Disease Control Products Guide for chemical control options (recommendations are different for each stage of growth that the strawberry plant is going through). Follow the directions on the product labels.
Symptoms of Anthracnose Fruit Rot
on Strawberry
Photo by Madeline Dowling, Clemson University, Bugwood.org
Salmon Colored Colletotrichum Spore Masses on Strawberry Fruit
Photo by Madeline Dowling, Clemson University, Bugwood.org
Anthracnose Fruit Rot
on Immature Strawberry
Photo by Madeline Dowling, Clemson University, 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
