English ivy leaves turning yellow? Here’s what to do.

I noticed dead spots on my ivy leaves this summer. What is this, and what can I do to help my plants?

— Paul Morgan, Park Ridge

There are two common types of leaf diseases on English ivy found in Illinois. One is caused by fungi and the other is caused by a bacterium. Both diseases can cause defoliation if severe, but your ivy does not sound like it is suffering too much at this point. Bacterial leaf spot disease begins as light green, water-soaked spots that enlarge and turn brown or brownish-black in the center. Initial leaf spots are usually angular and confined between the leaf veins. The spots may appear greasy or have a yellow border around them. Bacterial leaf spot can move into the stems, resulting in dieback of the ivy tips.

Fungal leaf spot produces large tan to brown spots on leaves. You may see black specks and fungal fruiting bodies on the dead tissue, which gives the spots a speckled appearance. The fungal fruiting bodies show up more easily after rain. Fungal leaf spot is generally brown in the center with a dark border. Sometimes, concentric rings give the spots a target appearance with spots scattered over the leaves. This disease can also infect stems, resulting in tip dieback.

Start by removing infected leaves and stems, if possible, to slow the spread of the disease. Prune out and dispose of all diseased leaves and stems in the fall while thinning the planting to increase air movement to promote drying. Dispose of plant debris in the garbage. Avoid getting the foliage wet as you water. Working with wet plants and splashing water can spread both diseases. Watering the foliage in the later afternoon or evening promotes the development and spread of these foliar diseases. Water early in the morning so the foliage can dry before night. These cultural practices should be sufficient to prevent the disease from becoming a major problem.

Sprays with fungicide can be effective against both bacterial and fungal leaf spot diseases if the problem continues to progress on your ivy after trying to be more careful with your cultural practices. They need to be applied on a regular schedule and reapplied after rainy periods. Look at new leaf tissue to best identify the disease you are contending with to choose the most effective control. Fungicides for bacterial leaf spot must be copper-based, or have copper in them (mancozeb, copper octanoate, copper sulfate, copper hydroxide). Other fungicides that work on fungal diseases will not control bacterial diseases.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.