Leaf spots are caused by a fungal infection that affects trees, shrubs, annuals, bulbous plants, vegetables, fruits, and lawns.
Leaf spot is characterized by concentrically zoned spots that appear on the leaves. Close inspection may reveal pinprick-sized fungal fruiting bodies. Spots may have a range of colors, but are frequently brown or slate-gray. In severe cases these spots merge, sometimes obscuring most of the leaf surface. Premature leaf drop may occur, but in some instances there is little damage or effect on the overall vigor of the plant. Blackspot on roses is a fungal leaf spot.
Leaf spot occurs on leaf blades, sheaths, and stems as circular to elongated purplish or brown spots with brown colored centers and purplish to dark brown borders. Spots may be found on turfgrass leaves throughout the site, indicating spread by wind borne spores. Crown and roots are frequently affected with a dark brown rot. Plants with crown infections are weakened and may die in hot, windy weather, resulting in a thinning out of the turf in scattered areas.
Bentgrasses, bluegrasses, fescues, and ryegrasses are susceptible to leaf spot. The fungus survives in infected grass plants or grass debris and may be seed borne. Spores are airborne.
The disease is favored by warm temperatures (70° — 90°F), high humidity, extended leaf wetness, and closely cropped turfgrass. It is more severe under high nitrogen fertilization.
Follow good management practices to prevent the development of leaf spot. Fungicides are usually not warranted.
Reduce shade and improve soil aeration and water drainage. Avoid dry spots, over fertilizing with nitrogen, and maintain as high a cutting height as possible. Avoid prolonged leaf wetness by irrigating in pre-dawn, or early morning hours. If possible, increase air movement.
Leaf spot usually is not serious enough in most places to warrant the use of fungicides although they may be used where leaf spot is severe. On landscape plants remove all affected parts and rake up and discard or burn any leaves that have already fallen to reduce the chance of re-infecting the plant again. This is especially true with rose bushes.
After removing all infected leaves, apply a fresh mulch around the base of the plant to reduce the chances of the fungus being splashed up on the leaves during rainfall or watering.
Bacterial leaf spots and blotches affect trees, shrubs, roses, perennials, annuals, bulbous plants, vegetables, fruits as well as some indoor plants.
The various symptoms of bacterial leaf spot may include a brown spots surrounded by a yellow halo. As the spots begin to merge, the entire leaf is killed and the leaf drops.
Treatment is similar to fungal leaf spot diseases. Practice good sanitation in fall and spray woody plants with sulfur in the winter.