Cause There have been several organisms associated with root rots and resulting branch diebacks in Oregon including Phytophthora sp. and Fusarium oxysporum. Both are favored by excessively wet soils but Phytophthora is favored by cool soils conditions while Fusarium is favored by warm soil.
Symptoms Root rots are usually first noticed by the flagging of individual stems, often in mid-summer. Leaves on these stems turn yellow then brown. Entire sections or sides of the shrub may become affected quite rapidly, looking almost as though it were burned. Plants may be stunted. Roots below affected branches are rotted. The entire plant may die, or it may persist for months in this state.
Cultural control
- Grow plants in well-drained soil. Soil can be amended with organic matter and/or gravel to improve drainage. Ensure that water does not stand in the planting area and if necessary improve surface drainage with tile.
- Avoid excessive watering during the growing season. Established Hebe plants should not require more than occasional irrigation during the warm summer months.
- 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.
Chemical control Only useful for Phytophthora once excess water problems have been addressed. There are no chemicals specifically labeled for this crop; however, many can be used if not phytotoxic.
Reference Raabe, R.D. 1985. Fusarium wilt of Hebe species. Plant Disease. 69:450-451.