Northwest berry Foundation

Management Detail

Phytophthora Root Rot

in Blueberries

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Latin name: Phytophthora spp.

Description:

Reason for Concern:
1) This disease occurs primarily on poorly drained sites.
2) The fungus resides in the soil and is transported in water and soil. Once established in the soil, it remains indefinitely.
3) Smaller, then larger roots die as the disease progresses.
4) Young plants with small root systems may die within a year of infection.
5) Mature plants show a decline in vigor over several years and may eventually die.
6) Yields are poor on infected plants.

Identification/Symptoms:
Early above-ground symptoms include yellowing or reddening of leaves with some burning of the margins and lack of new growth, and can look like nutrient deficiencies, Godronia canker or Crown Gall. As the disease damages roots, terminal leaves become small, and excessive defoliation occurs. Roots become soft and brown under the bark and the entire root system is reduced. Rot continues through the crown to stems, sometimes in a spiral fashion. As the infection progresses, crown tissue becomes brown under the bark. The edge of the advancing red-brown lesion is distinct from the adjacent unaffected tissue. The rot is firm, not soft. Plants in low areas in affected fields are characterized by dead or prematurely defoliating bushes. Infected young plants with small root systems may die the first year. Larger plants may slowly decline for 3 to 4 years before dying. Frequently, several canes on one side of the plant die, tracable to dead roots on that side.

Disease Cycle:
Infection is favored in warmer temperatures (between 20-32°C) and when soils are wet over long periods as a result of compaction, poor drainage or over-irrigation. The fungus grows as microscopic sized filaments within susceptible host plants, then consumes the host plant causing lesions that weaken or kill the plants by reducing or stopping the movement of water and nutrients. When conditions for growth become less favorable the fungus spores are able to survive in the soil or host tissue for many years, waiting for growth conditions to become suitable again.

Links:

Scouting:

  • Target declining plants.
  • Pull samples as soon as symptoms are seen. Keep sample refrigerated or cool. On healthy plants, the tissue just beneath the epidermis will be white; on plants with Phytophthora root rot, this tissue will be off color or brown (eventually for ELISA testing to determine phytothera; positives go for PCR testing turning dark brown as the tissue decays).
  • Monitor propagules.
  • Sort through plants before putting in field. Discard plants with poor root systems.

 
Cultural Controls:

  • Growers avoid planting in poorly drained fields or improve drainage by installing drainage tiles, planting on raised beds, incorporating gypsum, and/or amending soil with organic matter (which also improves tilth). They also avoid overwatering and they plant diseasefree, certified stock.
  • Some growers have discovered that soil solarization (covering the soil surface with plastic for several weeks during warm temperatures) prior to planting can delay onset of the disease for two years.

 

For information about chemical controls, check with our Pesticide Guide.

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Northwest Berry Foundation

Northwest Berry Foundation

© 2016

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