Cause A fungus-like organism, Phytophthora sp., has been found in rotted roots by the OSU Plant Clinic. Poorly drained soil or flooding encourages disease development. The organism survives unfavorable periods in soil and infected plant debris. Under favorable conditions, spores germinate and infect roots. After infection, the microorganism spreads mainly in the inner bark tissues of the root. They survive as various spores in the soil, container media, or infected roots. Movement of infected plants and/or soil can spread the microorganism.
Symptoms Aboveground symptoms include interveinal chlorosis, slowed shoot growth, limb dieback, wilting and death. Fine feeder roots are brittle and brown to reddish brown if they can be found at all. Browning of feeder roots often begins near the base of the root ball, easily seen in containers when the root ball is removed. Eventually the entire root system is destroyed.
Cultural control
- Container production should be on raised benches or gravel covered beds sloped to quickly drain excess water.
- Avoid reusing pots from a previous crop for propagation. If pots must be reused then wash off all debris and soak in a sanitizing solution or treat with aerated steam for 30 min.
- Avoid ponding of water around plants.
- Avoid over- or underwatering plants.
- Plant in a well-drained area or container media.
Chemical control Fungicide programs usually are effective only if combined in a management program with strict sanitation and good nursery management. Use fungicides as preventative treatments. The Group 4 and P7 fungicides used to manage Phytophthora do not kill this organism. They can only prevent establishment of the organism before it gets into the plant. They can also prevent continued growth if the organism is already inside the plant thereby delaying symptoms that might have developed. Once chemical activity has subsided with time, the organism can resume growth within infected plants.
- Fosphite at 1 to 2 quarts/100 gal water. Do not use copper products within 20 days of treatment and do not use spray adjuvants. Group P7 fungicide. 4-hr reentry.
- Mefenoxam 2 AQ at 0.98 to 1.96 fl oz/100 gal water as a soil drench or at 1.23 to 2.45 fl oz/1,000 sq ft followed by at least 0.5 inch rain or irrigation. Group 4 fungicide. No restrictions on reentry when used as a soil drench or media incorporation.
- MetaStar 2E at 1 to 4 fl oz/100 gal water as a drench. Group 4 fungicide. No restrictions on reentry when used as a soil drench or media incorporation.
- Monterey Garden Phos at 2 to 4 teaspoons/gal water as a foliar spray. Also labeled for soil drench, see label for details. Can be used in landscape sites. Group P7 fungicide. H
- Subdue MAXX at 1 to 2 fl oz/100 gal water. Use 1 pint solution/sq ft. Group 4 fungicide. 48-hr reentry.
- Terrazole 35 WP at 3.5 to 10 oz/100 gal water as a soil drench. Use only in commercial nurseries or greenhouses. Group 14 fungicide. 12-hr reentry.
Reference Vettraino, A.M., Antonacci, L., Flamini, L., Nipoti, P., Rossini, E., Righi, M., and Vannini, A. 2006. First report of crown rot of Photinia fraseri caused by Phytophthora cactorum. Plant Pathology 55:573.