||Bacterial blight on English ivy (Hedera helix)
Leaf spots on English ivy are caused by either a bacterium, Xanthomonas campestris, or a fungus, Colletotrichum trichellum. Both can cause defoliation, but the fungal leaf spot is more active in causing stem infection.
Symptoms and Diagnosis
Bacterial leaf spot first begins as light green, watersoaked spots that enlarge and become brown or brownish black in the center. On mature leaves the margin of the spot may be red. An infection in the leaf petiole causes the petiole to become black. Infection can move into the stem causing tips to turn black and die.
The fungal leaf spot produces large tan to brown spots on the leaves. They do not have a red margin. Black specks, fungal fruiting bodies, may be visible in the dead tissue, giving the spots a speckled appearance. The fungus can also infect stems, resulting in tip dieback.
Integrated Pest Management Strategies
1. Remove and destroy infected leaves and stems. Regardless of whether the spots were caused by a bacterial or fungal pathogen, removing diseased leaves will slow the spread of the disease.
2. Avoid wetting the foliage. Wetting the foliage, especially in late afternoon or evening, facilitates the development and spread of leaf spot organisms. Water early in the morning so the foliage dries before night.
3. Prune out and destroy all diseased plant parts in the fall. Thin the planting to allow better air movement and promote drying.
4. Live with the disease. The above cultural practices are generally sufficient to keep the disease from becoming a major problem.
5. Use fungicides. Sprays can be effective against both bacterial and fungal leaf spot diseases. They must be applied on a regular schedule and reapplied if rainfall is prevalent. copper fungicides are generally effective in controlling both leaf spots.
Strategies 1, 2, 3 and 4 are strictly organic approaches. For an organic approach to Strategy 5, consult the Organic Materials Review Institute (OMRI™) for appropriate organic copper products.