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Ground cover diseases

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Ground covers are valuable plants in the landscape; holding soil in place, filling in large spaces in landscapes and helping to moderate soil temperature extremes. Ground covers, however, are not maintenance-free. Like all plants, they can be susceptible to disease problems. There are several factors that can make them more susceptible than other plants.

They grow low to the ground and fairly close to each other, which can limit air circulation. This crowded planting causes their leaves to be wet for a long period of time after rainfall or irrigation, and this favors fungal infections. Ground covers are often grown in less than optimal conditions where other plants won’t grow. Plants grown in a stressful environment are more prone to disease. Fallen leaves from overhead trees are often left on top of ground covers. This promotes retention of moisture and provides a favorable environment for disease to grow and overwinter.

Disease name: Volutella blight

Pathogen name:  Volutella pachysandricola (fungus)

Hosts:  The ornamental ground cover Japanese pachysandra (Pachysandra terminalis) is susceptible to a serious, destructive stem and leaf blight called Volutella blight. The native Allegheny pachysandra (Pachysandra procumbens) is reported to be more tolerant of the disease.

Symptoms:

Volutella blight will cause leaf spots and stem cankers on pachysandra. Symptoms that develop in early spring are brown to tan leaf spots and can be confused with winter desiccation. The spots will enlarge and may eventually cover the entire leaf. Concentric circles form within the spots. Leaves eventually turn yellow and fall off the plant. Stems become infected, turn dark and die. During extended wet periods, orangish-pink fungal spore masses may be visible. Eventually, large patches of the ground cover may become infected and die.

Disease cycle:

Volutella overwinters as spores on infected leaves and stems. It is an opportunistic pathogen that tends to attack plants under stress. Stresses, such as overcrowding, winter injury, or shearing, may increase susceptibility to the disease. Older and injured plant parts of Japanese pachysandra are more susceptible. It can infect a plant any time during the growing season but is more common during periods of rainy weather. Infections tend to diminish as the weather becomes drier in the summer, but the high humidity created by heavily mulched beds can promote blight.

Management 

Cultural Management

Plant pachysandra in a site suited to its needs. Plants growing in less than optimal conditions are more likely to be stressed and more susceptible to infection. Water during dry periods and do so early in the day to allow foliage to dry out. Avoid working with plants when they are wet to prevent the spread of disease.

Sanitation is critical for management of Volutella. Remove and discard diseased leaves and plants immediately to keep infections from spreading to healthy plants. Clean up fallen leaves and diseased stems. Thin and divide overcrowded plants when the weather is dry, to improve air circulation. Avoid overuse of nitrogen fertilizer, which causes dense, succulent growth more susceptible to infection.

Chemical management

Fungicides sprays are available to treat Volutella blight.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For current pesticide recommendations, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).

Disease name: Phoma stem blight

Pathogen name:  Boeremia exigua (synonym Phoma exigua) (fungus)

Hosts:  Phoma stem blight is a serious fungal disease of vinca ground cover (Vinca minor), also known as periwinkle or myrtle. It can do serious damage to vinca and may kill out large patches of the ground cover.

Symptoms:

Phoma stem blight causes dark brown to black lesions on the stems of overwintering runners at the ground line. These lesions girdle the stem, killing the stems and attached leaves. In just a few weeks, entire clumps of plants may die.

Disease cycle:

Phoma stem blight fungus overwinters, and can live indefinitely in moist soil and plant debris. Soon after growth begins in spring, the new stems may wilt, turn dark brown to black, and die. The fungus frequently spreads from the stem lesions onto the leaf petioles and the base of the leaf. Phoma stem blight is more common in cool, wet weather.

Management:

Cultural Management

Phoma stem blight is a difficult disease to control once plants are infected, so prevention is important. Purchase only vigorous, healthy plants and plant them in a site adapted to their needs. Water during dry periods and do so early in the day to allow foliage to dry out. Avoid working with plants when they are wet to prevent the spread of disease. Thin and divide overcrowded plants when the weather is dry, to improve air circulation.

Sanitation is critical for management of Phoma stem blight. Remove and discard diseased leaves and plants immediately to keep infections from spreading to healthy plants. Clean up fallen leaves and diseased stems. Do not replant more vinca in the same area since the spores can be found on debris and in the soil for extended periods of time.

Chemical management

Fungicides treatments are available to treat phoma stem blight.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For current pesticide recommendations, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).

Disease name:  Bacterial and Fungal leaf spots of English ivy

Pathogen name:  Bacterium Xanthomonas campestris pathovar hederae and fungus Colletotrichum trichellum

Hosts:  English ivy (Hedera helix)

Symptoms:

Bacterial leaf spot produces spots that start out light green, with a water-soaked appearance. Later, the spots appear dark and greasy-looking and may have definite margins and a yellow halo visible when the leaf is lifted up to light. Often the spots crack with age and bacterial ooze may emerge from lesions when the conditions are wet and warm. Severe infection can cause leaf distortion, blight, and premature defoliation. The disease can also cause black cankers on stems, killing them.

The fungal leaf spot disease produces spots that are tan to brown and may be irregularly shaped. As the disease progresses, fruiting bodies that look like black specks can be seen within the spots. Lesions may develop on leaf stalks and stems, leading to dieback and defoliation.

Disease cycle:

Bacterial leaf spot overwinters in the soil and in infected debris. The bacterium enters through natural openings and wounds on the plant. Infection is more common in warm, wet weather. The fungal leaf spot overwinters as spores on infected plant debris. In spring, spores can be moved on the wind and by splashing rain, spreading the infection to more plants.

These diseases require wet leaf surfaces for an extended period of time, often more than 24 hours. For fungi, this allows spores to swell and germinate, and penetrate the leaf surface. Bacteria will multiply and enter through leaf stomata (a natural surface opening) or colonize in plant wounds. Leaf spot diseases may be more severe if leaves are infected when they first emerge in the spring. If the weather is dry during bud break, infection may occur later during wet weather after the leaves have expanded. .

Management:

Cultural Management

Bacterial and fungal leaf spot diseases can be managed, but prevention is a key component of that management. Purchase only vigorous, healthy plants and plant them in a site adapted to their needs. Water during dry periods and do so early in the day to allow foliage to dry out. Avoid working with plants when they are wet to prevent the spread of disease. Thin and divide overcrowded plants when the weather is dry, to improve air circulation.

Sanitation is critical for management of these diseases. Remove and discard diseased leaves and plants immediately to keep infections from spreading to healthy plants. Clean up fallen leaves and diseased stems.

Chemical management

Chemical treatments are available to treat the leaf spot diseases of English ivy.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For current pesticide recommendations, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).