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TREES & Plants

Ground cover diseases

Ground covers often make our jobs as gardeners easier by preventing weeds, holding soil in place, and helping to moderate soil temperature extremes. Ground covers, however, are not maintenance free. Like all plants, they can be susceptible to disease problems. In fact, ground covers are frequently used where conditions are favorable for disease.

  • They grow low to the ground and fairly close to each other, which can limit air circulation.
  • Their leaves are often wet, favoring fungal infections. This is the result of frequent rains, overhead watering, crowded plantings, and heavy shade.
  • They 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 wetness and provides a favorable environment for disease to grow and overwinter.

Some of the more common diseases of ground covers are described below.

VOLUTELLA STEM BLIGHT OF PACHYSANDRA

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 on pachysandra
This disease, caused bythe fungus Volutella pachysandricola, will cause leaf blight and stem cankers on most pachysandra species. Symptoms, first noticed in early spring as brown to tan leaf spots, 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 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.

Conditions Conducive to Disease

Volutella is an opportunistic pathogen. 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 the blight. Stresses, such as overcrowding, winter injury, or shearing, also may increase susceptibility to stem blight. Older and injured plant parts of Japanese pachysandra are more susceptible to the disease. Consider whether the site is one in which pachysandra can thrive. Pachysandra prefers filtered sun to full shade more than full sun conditions, and will be stressed by the latter and more susceptible to blight.

MANAGEMENT

Culural

See cultural control recommendations at the end of this leaflet.

Chemical

Fungicides listed for Volutella blight should be applied at 10-14 day intervals, beginning at the start of new growth or at the first sign of the disease, depending on the product selected and weather conditions.

FOLLOW LABEL INSTRUCTIONS

  • Copper (Dragon Copper)
  • Mancozeb (Dragon Mancozeb, many products)
  • Copper hydroxide (Ferti-lome Blackspot
  • Chlorothalonil
  •  

PHOMA STEM BLIGHT OF VINCA (PERIWINKLE)

Stem blight is a serious disease of periwinkle (Vinca minor), also known as myrtle.

Symptoms

Stem blight is caused by Phoma exigua var. exigua, a fungus that can live indefinitely in moist soil and plant debris. Dark brown to black lesions appear on stems of overwintering runners at the ground line. These lesions girdle the stem. Soon after growth begins in spring, the new stems may also wilt, turn dark brown to black, and die. In just a few weeks, entire clumps of plants may die. The fungus frequently spreads from the stem lesions onto the leaf petioles and the base of the leaf. This is a difficult disease to control once plants are infected, so prevention is important. Rhizoctonia blight appears similar to Phoma but no fruiting bodies are produced on the lesions. Be sure of which disease you have to increase your likelihood of growing healthy plants.

Conditions Conducive to Disease

Phoma blight is more common in cool, wet weather. Thinning overcrowded plants to improve air circulation and drying is helpful.

MANAGEMENT

Cultural

  • See cultural control at the end of this leaflet
  • Some cultivars are more resistant than others, although little has been published on this. For example, Vinca ‘Darts Blue’ is reported to resist the blight.

Chemical

Apply fungicides when disease symptoms first appear.

FOLLOW LABEL INSTRUCTIONS

  • Thiophanate-methyl (Bonide Bonomyl, Dragon 3336, or Ferti-lome Halt)
  • Copper sulfate pentahydrate (Phyton 27)
  • Mancozeb (Bonide Mancozeb or Dragon Mancozeb)
  •  

BACTERIAL OR FUNGAL LEAF SPOTS OF ENGLISH IVY

Although over forty pathogens cause leafspots on the popular ground cover English ivy (Hedera helix), the two most common foliar diseases are caused by a bacterium and a fungus. If you are using chemical control, it is important to determine which of the two pathogens are the cause because chemicals used for bacterial leaf spots are different from those used to treat fungal leaf spots. Fortunately, it is not difficult to determine if an ivy leaf spot is bacterial or funal.

Symptoms

Bacterial leaf spot of ivy
Bacterial leaf spot, caused by the bacterium Xanthomonas campestris pathovar hederae, is more common in warm weather. Initially, the leaf spots look light green and “water-soaked”. 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. Bacteria can also cause black cankers on stems, killing them. Fungal leaf spots are tan to brown and may be irregularly shaped. Often they produce concentric rings as the spot enlarges. You may be able to see fruiting bodies that look like black pepper within a spot. If fruiting bodies aren’t present, place the leaves in a plastic bag with a moist paper towel overnight. If the leaf spot is fungal, fruiting bodies should appear in the spot the next day. Fungal leaf spots do not cause stem cankers.

Conditions Conducive to These Diseases

These diseases require a wet leaf surface 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. Late infections are unsightly but rarely harm the plant.

MANAGEMENT

Cultural

See the cultural control at the end of this leaflet.

Chemical

Apply a bactericide for bacterial leaf spot when symptoms first appear.

FOLLOW LABEL INSTRUCTIONS

  • Copper (Dragon Copper)
  • Copper hydroxide (Ferti-lome Blackspot)
  • Copper sulfate pentahydrate (Phyton 27)
  • Mancozeb (Bonide Mancozeb or Dragon Mancozeb)

Apply a fungicide when disease symptoms first appear for fungal leaf spot.

FOLLOW LABEL INSTRUCTIONS

  • Thiophanate-methyl (Bonide Bonomyl, Dragon 3336, or Ferti-lome Halt)
  • Sulfur (Bonide Liquid Sulfur or Ferti-lome Sulfur)
  •  Potassium bicarbonate (Bonide Remedy)
  • Copper sulfate (Hi-Yield Bordeaux)
  •  

BOTRYTIS BLIGHT OR GRAY MOLD

Botrytis blight is a common fungal disease of many plants, including vinca, pachysandra, and ivy, as well as hundreds of trees and shrubs. There are several species of the fungus Botrytis that can cause blights. The most common is Botrytis cinerea.

Symptoms

Botrytis can affect leaves, stems, flowers and flower buds, seeds, seedlings, and bulbs. The fungus often colonizes dead plant parts first, and then spreads into living ones. Infected plant parts look blighted or dark with lots of gray fuzz in the infected area. This fuzz is actually fungal mycelia. Clouds of air-borne spores may be released from the mycelia in wet weather. Tiny, black specks may be visible in the gray fuzz. These are sclerotia, which are the fungal structures in which the disease overwinters. The fungus also overwinters in diseased plants.

Conditions Conducive to Disease

This disease is most prevalent in cool (55-65 degrees F), humid to rainy conditions. It attacks plants that are weakened by poor nutrition, low light intensity, low temperatures, or senescence (aging).

MANAGEMENT

Cultural

See the cultural control at the end of this leaflet.

Chemical

Apply one of the following fungicides.

FOLLOW LABEL INSTRUCTONS

  • Thiophanate-methyl (Bonide Bonomyl, Dragon 3336, or Ferti-lome Halt)
  • Mancozeb (Bonide Mancozeb or Dragon Mancozeb)
  • Potassium bicarbonate (Bonide Remedy)
  •  

CULTURAL CONTROL FOR GROUND COVER DISEASES

  • Purchase healthy plants that are free of disease.
  • Purchase species or cultivars that are considered disease tolerant or resistant.
  • Select plants that are right for the site conditions. Plants growing in less than optimal conditions are more likely to be stressed and more susceptible to infection.
  • Plants should be watered during dry periods by using drip irrigation and/or by watering early in the day to allow foliage to dry out. In established beds, avoid overhead watering or watering in the evening.
  • Avoid working with plants when they are wet to prevent the spread of disease.
  • Remove and discard diseased leaves and plants immediately to keep infections from spreading to healthy plants.
  • Clean up fallen leaves and other debris that has accumulated on top of ground covers.
  • Thin, prune, and divide overcrowded plants in early spring, when weather is dry, to improve air circulation.
  • Avoid over-fertilization, which causes dense, succulent growth susceptible to infection.


Refer to the Illinois Urban Pest Management Handbook (University of Illinois Cooperative Extension Service) for a complete listing of chemical recommendations. Use pesticides safely and wisely; read and follow label directions.

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.