Phytophthora species are important soil-borne, fungus-like pathogens that attack the root systems, trunks, and fruit of citrus trees at any age.
Identification
Leaf symptoms
- Leaves may show yellowing (chlorosis) or wilting
- Other diseases or disorders mimic the symptoms of Phytophthora (HLB, over-fertilization, or salt damage)
Root symptoms
- Soft, water-soaked root cortex
- Cortex sloughs off (comes off to touch) to leave thread-like tip
Soil Collection
- Select declining tree and label tree.
- Sanitize hands and wear gloves.
- Label sample bag.
- Collect ¼ cup of soil from middle area of roots (if healthy root system) or from bottom of roots (if most roots have rotted away).
- Seal sample bag.
- Discard gloves and wash hands with soap and water.
Soil Testing
- Stir or shake soil sample bag to loosen any clumps of soil. Fill each compartment of two ice cube trays ¼ full of soil sample.
- Fill each compartment with water and stir. Skim off floating soil/potting medium with a plastic spoon.
- Use a hole punch to make ¼ inch leaf disks. Place four citrus leaf disks into each compartment.
- Incubate in dark room or cabinet at approximately 74°F for 48 to 72 hours.
- Place leaf disks onto a slide with a drop of water and observe with microscope.
- Use a compound microscope with a 400x magnification (10x ocular lens and a 40x objective lens) or a dissecting scope with 500x to 600x magnification to determine the presence or absence of sporangia (spore producing structures).
Diagnosing Phytophthora
- There are two causal species of Phytophthora.
- Phytophthora nicotianae is the common cause of brown rot, foot rot, and root rot.
- Phytophthora palmivora causes brown rot and root rot in poor soils with high water tables.
- Knowledge of species and determining the type of sporangium are important for disease diagnosis.
- Properly dispose of infected plants.
General Sanitation Practices
- Do not enter greenhouses after visiting citrus groves.
- Keep head house area and greenhouse walkways swept and free of debris.
- Don’t use surface water as an irrigation water source.
- It is recommended to have a disinfesting copper footbath at each house entry.
Tools
- Shovels should be disinfested before and after each use and should NEVER touch the floor during storage.
- Hose nozzles should never contact the ground.
- Hose nozzles should remain on bench tops or hooks when stored.
- If the hose nozzle contacts the ground, decontaminate immediately (see other side).
Buckets, Pots, and Tubs
- Should only be filled with clean potting media.
- If pots have sat on the floor, do not stack pots on top of one another.
- Do not store pots directly on the ground or within a splash zone.
Potting Media
- Where possible, source potting media from Phytophthora-free supplier.
- Store potting media on a concrete pad and periodically disinfest the pad.
- Storage areas should be protected from wind and rain.
- Pile should be kept covered.
- Restrict access to media storage area.
- Station a copper footbath at entrance of storage area.
- Footwear should be disinfested at each entry.
- Tractor tires, scoops, and shovels used to move media should be disinfested as needed.
General Sanitation Management
- Sanitizing should be at the start of each workday for personnel and tools, when moving among plants within or between benches, or when moving from one house to another within the nursery.
- All equipment should be re-sanitized if dropped or if used in a non-clean area.
- When hand watering, keep the water splash to a minimum.
- Nursery workers should not stand on or use tables or pots as a step.
