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Beginner

Scientific Name
Phytophthora cactorum

Identification

• Infects strawberry bloom and green or mature fruit.
  
• Occurs where berries are exposed to soil.
  
• Infected blossom clusters turn brown and die.
  
• Green fruit become hard and leathery.
  
• Lesions are not distinct but are usually somewhat soft and are sometimes dull pink to lavender or purple.
  
• Ripe fruit develops a purplish colour and foul odour and taste; symptoms are most often noticed on ripening fruit.
  
• Slicing infected berries will reveal darkened inner tissues.
  
• White mould may grow from the diseased fruit.

Often Confused With
Anthracnose
Botrytis grey mould

Period of Activity
Infection can take place anytime between bloom and harvest if spores are splashed or washed onto bloom or fruit. Leather rot is worse under cool, wet harvest conditions.

Scouting Notes
Scout in areas of the field where standing water or surface water run-off have occurred. Expect problems where straw is thin, blown away or washed away, exposing blossoms and fruit to the soil. Problems are most likely to develop after a heavy rain or irrigation.

Pick-your-own customers and workers are often the first to discover leather rot . Complaints of foul, sewage or chemical smells are common where leather rot occurs.

Thresholds
None established.

Advanced

Scientific Name
Phytophthora cactorum

Leather rot is caused by the fungus, Phytophthora cactorum, which is commonly found in soil and has a wide host range. The same fungus can cause Phytophthora crown rot, although the two diseases may not occur in the same time or place.

Identification
Leather rot can infect strawberry bloom and green or mature fruit. Infected blossom clusters turn brown and die. Green fruit become hard and leathery. Leather rot symptoms are most often noticed on ripening fruit. Infected mature berries do not have distinct lesions but are usually somewhat softer than healthy fruit and are sometimes dull pink to lavender or purple. Slicing infected berries will reveal darkened inner tissues. These fruit develop a purplish colour and a foul odour and taste. White mould may grow from the diseased tissues.

Often Confused With
Anthracnose (Distinct round orange, brown or black lesions on sides of fruit.)
Botrytis grey mould (Lesions associated with the calyx end of the fruit, grey or beige spores.)

(Leather rot can be distinguished by its foul odour and taste and lack of a distinct border or lesion to indicate the infection.)

Biology
Phytophthora is a soil-borne fungus that persists in the soil as thick-walled resting spores (oospores), which can survive in a dormant state for many years. Overwintering mummified fruit are a source of these oospores. When the soil is moist or wet, some of the oospores in the soil germinate and form reproductive structures (sporangia), which release mobile, infectious spores (zoospores). These microscopic zoospores are released into the soil when it is flooded and swim to the surface using tail-like structures. A leather rot epidemic can begin when strawberry fruit become infected after lying in water containing zoospores or when the infected water is splashed by rain or irrigation.

If conditions are wet or humid, the leather rot fungus forms a white fungal growth on the surface of the infected fruit. Spores are spread through the air by wind and rain. They infect the fruit most readily under wet conditions that persist for one to several hours at temperatures between 15°C and 28°C (59- 82°F). Sporangia are produced on newly infected fruit under these wet conditions. The leather rot fungus forms oospores within infected fruit that enter the soil when the fruit decays.

Leather rot is favoured by warm weather with abundant rainfall. It can also become serious when cool weather occurs with frequent fog and morning dews.

Period of Activity
Infection can take place anytime between bloom and harvest, if spores are splashed or washed from soil onto bloom or fruit.

Scouting Notes
Scout in areas of the field where standing water or surface water run-off have occurred. Expect problems where straw is thin, blown away or washed away, exposing blossoms and fruit to the soil.

Customers are often the first to discover leather rot in pick-your-own fields. Complaints of foul sewage or chemical smells are common where leather rot occurs.

Thresholds
None established

Management Notes

• Use a thick layer of straw much between the rows to prevent berries from touching the soil and soil from splashing the fruit.
  
• Plastic mulch under the plants will also protect fruit from the soil and prevent leather rot infection.
  
• Conditions that favor Botrytis will also favor leather rot.
  
• Grow strawberries only on sites with excellent soil drainage, where standing water does not occur.
  
• Growing strawberries on raised bed or ridges can reduce leather rot problems.