Many landscapes incorporate English ivy, Hedera helix, into shady areas. This plant also thrives in full sun, works as a ground cover, or can climb to become a vine. As the plants grow and fill in the landscape area, diseases may cause problems--especially in wet or humid weather and in shady locations.
English ivy is susceptible to two difficult-to-distinguish diseases that cause spots, stem cankers, and thinned areas as plants die. Either disease may occur in Illinois. One is caused by a bacterium and the other by a fungus, so management varies slightly. English ivy in exposed sites may also suffer some winter burn, resulting in necrotic blotches and leaf edge burn. Injury increases disease incidence because it provides more sites for infection.
Bacterial leaf spot and stem canker is the more common disease in Illinois. It thrives in warm, wet weather such as we have experienced in much of the state lately. Bacterial leaf spot first appears as small, circular, dark green, water-soaked (oily) lesions on the leaves. As these enlarge, they have reddish brown to black centers with a water-soaked margin and (sometimes) a yellow halo. The spots also crack with age. The bacterium may cause black cankers on the stems and petioles; those stems die, often with black tips. The bacterial pathogen is easily spread from plant to plant by splashing water.
The fungal leaf spots are caused by a variety of fungal species. They cause round to irregular spots in a variety of colors. Often a series of concentric rings can be seen in the spots. Look closely on the spots for small black specks (pinhead-sized), which are fruiting structures containing spores of fungi. These fruiting bodies may be embedded in the spots (pycnidia), or they may be on the surface and have black hairlike structures called setae (anthracnose). Bacterial spots do not have fruiting structures because bacteria do not form spores. The diseases are easily distinguished in a lab but can be confusing in the field.
If you establish a bed of ivy, look closely at new plants so that you do not introduce disease. These diseases are very common in Illinois, so if a friend is thinning a planting and sharing plants with you, inspect the established bed for disease problems first. Remove any questionable leaves or stems from transplants. Also, remove old leaves and debris from the beds each spring before new growth starts. Always work with the plants when they are dry to avoid spread of the pathogen. Because these diseases require water on the foliage to infect the blades, water the soil rather than the foliage where possible. Consider using soaker hoses in these beds. Water early in the day so that wet foliage can dry quickly.
We would like to manage these diseases by using resistant varieties. Although work is in progress to identify such varieties, those with good resistance have not been found. Look for disease resistance indicated on tags in the nursery. If leaf spots have been severe in the past, apply fungicides, starting when new leaf growth begins in the spring. Registered chemicals are listed in the Illinois Commercial Landscape and Turfgrass Pest Management Handbook and the Home Yard and Garden Pest Guide. Because the chemicals are protectants, labels usually specify that they be repeated at 7- to 10-day intervals as long as wet weather persists in the spring and early summer. If you choose a systemic product, you do not have to spray as often. Chemical mobility is listed at the end of the disease chapters in the pest guides listed. A few chemicals are listed for both diseases; if you cannot determine which disease is present, use a product listed for both. Try to improve air movement by thinning the stand and pruning surrounding plants. For more information, consult Report on Plant Disease (RPD), no. 652, "Leaf Spot Diseases of English Ivy."