What Causes Brown Spots on Strawberries?

brown spots on strawberriesQ: What Causes Brown Spots on Strawberries?

On January 3rd, 2017, Jim asked:

I made an incredible raised bed garden just for strawberry plants. The plants have bloomed and now the berrys are turning brown. What is the likely cause and is there a remendy for this situation? I have planted strawberry plants in a raised bed planter using organic soil … I’m in central Florida and the plants are doing splendid, however, the berry turns brown and it appears as if the seeds on the berry fall off. I have found no reference to this situation in any websites I have perused. I’m hoping you can clue me in to whats happening, or at least give me the proper words for the obituary.

Answer to: What Causes Brown Spots on Strawberries?

Jim,
It can be extremely frustrating to spend as much time and effort making a great strawberry bed only to have your strawberries turn brown or rot on the plants before you get to enjoy the sweet fruits of your labor.  There are several things that can cause brown spots on strawberries, but the most common two are rot caused by partial animal or insect feeding and a fungal organism.  The first (pests) is likely self-explanatory.  The second, however, can be more insidious.  This post will deal with the second major cause of brown spots on strawberries: leather rot.

Leather Rot Causes Brown Spots on Strawberries

Leather rot is a relatively common pathogenic fungus (Phytophthora cactorum) that can affect strawberries in any stage of development. It can infect green strawberries.  It can infect ripe strawberries.  And, it typically only causes minimal damage to commercial farmers. However, home gardeners can loose many strawberries to the fungus if care isn’t taken to avoid infection.

Infection of healthy fruit and subsequent brown spots on strawberries from leather rot typically happens during periods of wet weather.  Rainy April, May, and June weather sets the stage for infection.  The spores of the fungus stay in the soil and can infect strawberries when there are periods of extended wetness.  If water remains in contact with fruit for an hour when the temperature is between 62 and 77 degrees Fahrenheit, infection is likely if spores are present.  Brown spots on strawberries will come soon after infection as the pathogenic fungus sets up shop in your fruit.

Brown spots on strawberries are most easily seen on immature fruit.  If the fruit is still green or white, the spots will be most visible.  Ripe fruit can get leather rot also.  However, the brown spots will not usually be as noticeable.  Sometimes, the discoloration will even be a purple color or just a darkening of the strawberry in the infected area.  Usually, along with discoloration, there will be an odor and unpleasant taste in infected berries.

brown spots strawberriesHow to Prevent Brown Spots on Strawberries

Preventing leather rot infections is the key to harvesting healthy strawberries.

  1. The first and critical step is to pick a location for your strawberry bed that is well-drained.  Good soil drainage prevents standing water.  The absence of standing water makes difficult for the fungus to remain in contact with strawberries long enough to infect them.
  2. Use a thick barrier mulch. A good layer of clean straw can prevent the spread of leather rot.  Clean straw help reduce or eliminate splash from rain.  It can assist in drainage.  And, it keeps the strawberries themselves from resting on the soil where the pathogenic fungus lurks.
  3. Avoid shade.  Plant your strawberries in full sun to minimize the conditions favorable to fungal infection.
  4. Plant the rows parallel to the direction of the prevailing winds.  Most locations receive there weather, more or less, from the same general direction.  If you plant your strawberry rows with the prevailing wind, the fruit and leaves of your strawberry plants will dry more quickly.
  5. Avoid excessively dense plantings.  Be sure to maintain adequate space between your strawberry plants to facilitate drying.  Additionally, inappropriate application of nitrogen fertilizer can cause dense vegetative growth that will shade the berries (see 2. above!) and create an environment conducive to infection.
  6. Pick fruit early.  As soon as the plants dry each day, go picking!  Removing the strawberries as soon as possible during the day can reduce infections.
  7. Watch for and remove fruits with any brown spots on strawberries.  It is vital for the health of remaining plants that strawberries with brown spots be removed as quickly as possible from the strawberry patch.  If strawberries with leather rot are left in the field, the causal organism will multiply and spread.
  8. As a last approach, fungicides can be used.

Strawberries with Brown Spots: Conclusion

Pay attention to your strawberries!  If they get brown spots, cull them as soon as possible.  Leather rot can be a pain in the neck.  If you set up your strawberry bed in a way that helps the fungus instead of impairing it, remedy as many factors as you can.  Good luck!

leather rot strawberries with brown spots

[ brown spots on strawberries ]

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