Sample of the Week

July 1, 2019: Hollyhock Rust

Josephine Mgbechi-Ezeri and Caroline Jackson
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Have strange orange and brown bumps plagued your flower beds this year? The prolonged cool temperatures and heavy precipitation this spring have allowed fungal pathogens to flourish. Here is one heavy infestation of Hollyhock rust, a disease that is caused by the fungal pathogen Puccinia malvacearum. Common hosts include Alcea rosea, (hollyhock), Abutilon spp. (flowering maple), Malvaceae spp. (rose mallow), and common weed mallow. It is one of the most common diseases of hollyhock.

hollyhock rust, figure 1
Figure 1. Yellow spots on upper leaf surface. (Photo Credit: Caroline Jackson, University of Missouri Plant Diagnostic Clinic)

Symptoms of the disease include the yellow to red spots on upper leaf surface, and brown pustules that appear blister-like occur on lower leaf surface and stem. Leaves that are heavily infected often wilt, turn brown and die. This disease is the most common of hollyhock and can spread rapidly from leaf to leaf. The fungus overwinters in the infected plant materials, and in the spring produce spores that are dispersed by wind to initiate infection on new plants.

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Figure 2. Orange brown pustules on underside of leaf. (Photo Credit: Caroline Jackson, University of Missouri Plant Diagnostic Clinic)

For appropriate diagnosis, the MU Plant Diagnostic Clinic can help you confirm if your plant has this disease. Please visit our plant clinic website and follow the instructions for collecting, packaging and shipping samples to the clinic.

More resources about Hollyhock Rust: https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/rusts/rust-of-hollyhock.aspx

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Figure 3. Orange to brown pustules on stem characteristic of rust pathogens. (Photo Credit: Josephine Mgbechi-Ezeri, University of Missouri Plant Diagnostic Clinic)

Good cultural practices such as appropriate spacing between plants to allow better air flow to reduce leaf wetness will help prevent this disease and also manage it. Management can include weed control of Malva rotundifolia, or common mallow, which can act as an inoculum reservoir. Sanitation practices such as removal and burning of infected hollyhock stalks, stems, leaves or other host material will further reduce spores for infection. Fungicide products can be applied from the start of growing season (when the leaves are expanding before the first sign of the disease) through mid-July. Applications should be made frequently or when rainfall exceeds ½ inch. Fungicides recommended for control include chlorothalonil, sulfur, mancozeb, and maneb. Note that fungicides are preventative and do not cure already existing disease.

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Figure 4. Teliospores of rust fungus Puccinia heterospora. (Photo Credit: Caroline Jackson, University of Missouri Plant Diagnostic Clinic)

Previous samples

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    May 29, 2019: Anthracnose Disease of Trees

    Josephine Mgbechi-Ezeri and Caroline Jackson
    PDF version

    What is going on with the sycamore trees this year? Have you all gotten calls about a lot of die back on leaves? These are some of the questions the plant diagnostic clinic has been getting lately in addition to physical samples submitted for diagnosis. The prolonged cool and wet conditions in Missouri this spring have been favorable for the pathogens that cause anthracnose disease on shade trees. Anthracnose is a general term for fungal diseases that attack shade trees and shrubs expressing a black or brown necrotic lesions on leaves. The disease causes deformation of leaves around the lesion area and in the case of severe infection can cause complete defoliation of the tree. The fungal pathogens associated with anthracnose diseases are morphologically related however, they are host specific. Trees that are commonly affected include elm, ash, white oak, sycamore, maple, walnut, and dogwood (Figures 1 to 6).

    anthracnose ash, figure 1
    Figure 1. Symptom of anthracnose disease on ash leaves. (Photo credit: MU-Plant Diagnostic Clinic)

    anthracnose white oak, figure 2
    Figure 2. Symptom of anthracnose disease on white oak (Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org)

    anthracnose sycamore, figure 3
    Figure 3. Symptom of anthracnose disease on sycamore (Photo credit: Robert L. Anderson, USDA Forest Service, Bugwood.org)

    anthracnose maple, figure 4
    Figure 4. Symptom of anthracnose disease on maple (Photo credit: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org)

    anthracnose walnut, figure 5
    Figure 5. Symptom of anthracnose disease on black walnut (Photo credit: Lorraine Graney, Bartlett Tree Experts Bugwood.org)

    anthracnose dogwood, figure 6
    Figure 6. Symptom of anthracnose disease on dogwood (Photo credit: John Hartman, University of Kentucky, Bugwood.org)

    The disease pathogens overwinter in infected plant material. As the temperature begins to warm up in late winter to early spring, the fungus becomes active, producing spores that are dispersed by rain and wind on newly emerging leaves. The spores initiate infection in the leaves. Later in summer under favorable conditions, a new generation of spores reproduce and cause continuous infection on the leaves. The symptoms expressed and severity of infection depends on the host as well as the environmental conditions. Although the disease causes defoliation, it does not have any serious impact on tree health. However, in the case of severe infection and defoliation occurring in multiple years, it can weaken the tree and increase vulnerability to other diseases and pests.

    Disease management

    Anthracnose disease of shade trees is mostly a cosmetic problem, thus chemical control is not warranted. Cultural and sanitation practices such as planting resistant varieties, pruning dead or dying branches and raking fallen plant debris will help to reduce inoculum. Select a good site with good air circulation and sun penetration. Provide adequate nutrient and water when necessary to improve plant vigor.

    For appropriate diagnosis, the MU Plant Diagnostic Clinic can help you confirm if your plant has this disease. Please visit our website and follow the instructions for collecting, packaging and shipping samples to the clinic.

    For appropriate identification, the MU Plant Diagnostic Clinic can help you confirm your insect species and provide you with the best way to manage them. Please visit our MU Plant Diagnostic Clinic website and follow the instructions for collecting, packaging and shipping samples to the clinic.

    For additional information on anthracnose diseases of shade trees, please refer to the publication by University of Illinois Extension: Anthracnose Disease of Shade Trees.

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    January 29, 2019: Ground Beetle

    ground beetleGround beetles make up the largest group of insects in the order Coleoptera belonging to the family Carabidae. They are small to moderate in size measuring between 1/8 and 3/4 inches long and they vary in shapes and colors. They are commonly found in different environments such as forests, landscapes and fields. They are attracted to light and sometimes can become a nuisance when they occur in large numbers inside houses and buildings. These beetles wander into buildings through cracks and openings and can be found in hidden damp areas. Ground beetles can be confused with cockroaches, carpet beetles or other household pests.

    The beetles live temporarily indoors and do not establish there. Female adults lay eggs in soil, upon hatching the larvae pupate and overwinter in the soil. Adult ground beetle emerge in the spring and some can live for several years. Most ground beetles complete their developmental stages within 1 year.

    Ground beetles do not cause any damage to buildings and furniture, and they are not harmful to human and pets. Most larvae and adult ground beetles are beneficial by feeding on other insects, and therefore control is not necessary. However, in circumstances where these beetles are nuisance pests in buildings, non-chemical strategies such as sealing and repairing points of entry, eliminating hiding places (i.e. mulch, stones, plant debris, tall grasses and weeds) around the home can be helpful in mitigating invasion. In extremely severe cases, spraying insecticide around the house foundation, doorways and other points of entry may be necessary.

    For appropriate identification, the MU Plant Diagnostic Clinic can help you confirm your insect species and provide you with the best way to manage them. Please visit our MU Plant Diagnostic Clinic website and follow the instructions for collecting, packaging and shipping samples to the clinic.

    For more information on ground beetles, see the article by Penn State's Department of Entomology: https://ento.psu.edu/extension/factsheets/ground-beetles.

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    November 19, 2018: Maple Tar Spot

    Tar spot symptom on silver maple leafTar spot is caused by several fungal species in the genus Rhytisma. Tar spot is generally a cosmetic disease and does not cause any health problem on trees. Early infection on leaves appear as yellowish spots approximately 1/8 inch in diameter and may be inconspicuous in early summer. As the disease progresses in mid to late summer, these spots enlarge, turn dark in color and become raised forming tar-like structure on the leaves. The disease may cause premature defoliation, however this does not have any significant effect on the tree health. Tar spot pathogens overwinter on plant materials and are spread by wind on to new foliage as leaves begin to emerge in the spring.

    Tar spot can be controlled by raking and removing plant debris in the fall. This will help to destroy overwintering inoculum that can infect new leaves in the following spring. Fungicides labelled for tar spot control is rarely recommended since the disease does not cause any severe damage to the tree.

    For appropriate diagnosis, the MU Plant Diagnostic Clinic can help you confirm if your plant has this disease. Please visit our website the sample submission page and follow the instructions for collecting, packaging and shipping samples to the clinic.

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    November 12, 2018: Elm Anthracnose

    elm anthracnoseThe plant clinic received Chinese elm sample diagnosed with black leaf spot, a fungal disease caused by Stegophora ulmea. Black leaf spot also described as elm anthracnose disease appears as small tan, brown, black or tar-like spots on upper leaf surface. As the disease progresses, spots may coalesce to form unevenly-shaped leaf blotches. Elm anthracnose is mostly common about the time for normal leaf fall and may not cause serious damage to trees. In severe infection, elm anthracnose can cause premature defoliation of susceptible trees. Repeated defoliation may cause weakness, increase susceptibility to diseases and eventually death of the tree. The pathogen overwinters in infected buds and plant debris. During cool and moist weather conditions, spores are discharged and spread by wind and rain. This disease can be managed by raking infected plant debris and pruning dead wood to reduce inoculum build-up for future infection.

    For appropriate diagnosis, the MU Plant Diagnostic Clinic can help you confirm if your plant has this disease. Please visit our website the sample submission page and follow the instructions for collecting, packaging and shipping samples to the clinic.