English ivy can make a beautiful, lush ground cover. Unfortunately, English ivy is also susceptible to two diseases that cause spots, stem cankers, and thinned areas as plants die. The two diseases look quite a bit alike, even though one disease is caused by a fungus and the other is caused by a bacterial pathogen. To use the correct disease management, accurate identification of the pathogen type is necessary.
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; 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, which are fruiting structures con-taining spores of fungi. 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 this year, look closely at new plants to be certain that you do not introduce diseased plants. Before accepting plants from someone else’s ivy bed, inspect the established bed for disease problems. Remove any questionable leaves or stems from transplants. It is also a good idea to 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 when possible. Water early in the day so that wet foliage will dry quickly.
If leaf spots have been severe in the past, apply fungicides beginning with new-leaf growth in the spring. Registered chemicals are listed in the Illinois Commercial Landscape and Turfgrass Pest Management Handbook 2000 and the Illinois Homeowners’ Guide to Pest Management. Because the chemicals are protectants, the labels usually specify that applications be repeated at 7- to 10-day intervals, as long as wet weather persists in the spring and early summer. Few chemicals protect plants from the bacterial leaf spot and stem canker. The copper compounds and Chipco Aliette may help, but control is not complete. Improve air movement in the area by thinning the stand and pruning surrounding plants. For more information about these diseases, consult Report on Plant Diseases No. 652, Leaf Spot Diseases of English Ivy.