Key Features
- Stunting or blighted branches
- Reddish-brown canker at crown
- Plant death
Symptoms
Phythophthora is a group of soil-borne plant pathogens that attack many host species. A few generalizations can be made about symptom development. Plants with mild root rot are stunted and produce fewer and smaller leaves than normal. Moderate root rot will result in drought-like symptoms: leaves wilt, turn red, or show signs of iron chlorosis. Severe rot will result in lodging (the plant falls over) or death. A red canker may be seen at the soil line with moderate and severe infections. The tissue (wood or vascular tissue) inside stems may be stained red. With every infection, roots darken and rot, making the plant susceptible to blowing over. The stem and crown may easily pull away from the root system.
Biology
Phytophthora overwinters in most soils. Wet soils and standing water promote spore release. These spores are capable of moving through films of water toward young and weak plants. Therefore, poorly drained soil or wet sites favor the disease. Spores infect feeder roots just behind the root cap or can be splashed to leaves or stems.
Management Recommendations
Fungicides cannot "cure" this disease. Remove and destroy infected plants. Replant with non-hosts, as even resistant varieties can succumb if inoculation levels are high. Plant susceptible plants in well-drained locations. Test drainage conditions by filling the hole with water: Water that drains within 24 hours can be assumed to provide sufficient drainage. If standing water remains after 48 hours, planting material should be assessed to determine the tolerance of poorly drained sites. Drain tile or raised beds can be used in poor draining locations to decrease this disease. Within species of certain plants, some cultivars are highly susceptible and others are less so. There are currently no fungicides registered for homeowner use against Phytophthora root rot.
Effective Pesticides
Active Ingredients include: Phosphorous acid salts
Resources
