Cause Although Armillaria root rot has been reported from all states, Phytophthora spp. have been sent into the OSU Plant Clinic several times. Native plant nurseries have experienced problems with P. cactorum, P. pini and P. occultans on C. integerrimus, C. sanguineus and C. velutinus.
Symptoms Root and stem rots.
Cultural control
- Improve drainage where plants are grown.
- Do not overwater. Ceanothus are best grown in sites where no summer irrigation is received after the plants are established.
- 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.
- Remove and destroy infected plants.
Chemical control For control of Phytophthora focus on cultural controls. 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/1000 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 is labeled as a soil spray at 1.25 to 2.5 fl oz/1000 sq ft, irrigated in with 0.5 inch water, if rain does not fall in 24 hours. Not a curative treatment. Group 4 fungicide. 48-hr reentry.
- Terrazole 35 WP at 3.5 to 10 oz/100 gal water. Group 14 fungicide. 12-hr reentry.
References Hansen, E., Reeser, P., Sutton, W., and Sims, L. 2012. Host and habitat index for Phytophthora species in Oregon. Forest Phytophthoras 2(1). doi: 10.5399/osu/fp.2.1.3026
Reeser, M.P.W., Sutton, W., Hansen, E., Goheen, E.M., Fieland, V., and Grünwald, N.J. 2015. First report of Phytophthora occultans causing root and collar rot on Ceanothus, boxwood, rhododendron, and other hosts in horticultural nurseries in Oregon, USA. Plant Disease 99:1282-1283.