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Cause Several fungal leaf spots have been reported from the Pacific Northwest. These include Phyllosticta philoprina, Gloeosporium aquifolii, Phoma spp., and Sclerophoma sp. (scab). The OSU Plant Clinic has found some of these fungi and others. This has included Rhytisma sp. (tar spot), Chrysomyxa ilicina (rust) and many others that were not specifically identified. Most of these have not been a major problem for holly production. Some can be secondary invaders of leaves injured by excessive cold or heat or by mechanical injury. An older Extension Mimeo from State College of Washington indicates that spots are numerous on trees that suffered from drought the previous year or that have been grown in unfavorable soil.
Symptoms Yellow, gray or brown spots, often surrounded by a purple margin and usually appearing on older leaves.
The following is a description of tar spot from Japan: Yellowish spots, roughly circular and about 1-4 mm in diameter, arise in spring on newly developing leaves. A black stromatal layer develops in 5 to 10 days and gradually grows in thickness during the fall.
Cultural control Tactics used to control Phytophthora Leaf and Twig Blight should work just as well for many of these leaf spotting fungi.
- Control weeds and brambles to help air circulation.
- Select a site that permits good air drainage.
- Space and prune trees to permit good air circulation.
- Remove and destroy fallen leaves and dead infected twigs during the summer. If few in number, remove from the tree.
Chemical control
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
- Banner MAXX at 5 to 8 fl oz/100 gal water may be effective. Group 3 fungicide. 12-hr reentry.
- Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- CuPRO 5000 at 1.5 to 5 lb/A but only up to 2 lb/A when new growth is present. Group M1 fungicide. 48-hr reentry.
- Orkestra at 4 to 10 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Suto, Y. 2009. Three ascomycetes on leaves of evergreen Ilex trees from Japan: Rhytisma ilicis-integrae sp. nov., R. ilicis-latifoliae, and R. ilicis-pedunculosae sp. nov. Mycoscience, 50:357-368.