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Blueberry Flowers Turning Brown and Falling Off

In late August, you may encounter flowers blooming on the blueberry bushes. These flowers are more than ornamental elements on the bushes. They actually turn into berries after 90 to 135 days after blooming, depending on the blueberry variety.

If your blueberry flowers are turning brown and falling off, you don’t have to worry as long as they leave behind green developing fruit. However, when entire flowers, plus the stem, turn brown and fall off, the plant is likely stressed because it lacks sufficient water or has blossom blight. 

As your blueberries begin to bloom, you need to be on the lookout for any browning that occurs for the wrong reasons. Typically, browning of blueberry flowers means they have been pollinated. Unhealthy browning can occur through all stages of development of the blueberry plant, and this article explores the different causes in further detail as the plant grows. 

Pre Pollination Browning

Blueberry flowers turning brown before pollination are typically suffering from fungal diseases. The major fungal problem found on these flowers during this time is:

Botrytis Blossom Blight

This disease is caused by the fungus Botrytis cinerea, which affects the senescent tissues on a plant. The corollas on the blueberry flowers are senescent, meaning they grow old and can no longer replicate. They become vulnerable to botrytis blossom blight just before they become senescent. 

The fungus finds its way into the ovary of the flower and later into the stem, which is also known as the peduncle. Unfortunately, the fungus can stay dormant in an immature blueberry plant and get revived when they encounter favorable weather conditions. Because blueberries are perennial plants having a latent fungal infection among your crop can lead to huge losses of healthy fruits.

When affected by this disease, the blossoms will turn brown before powdery gray spores cover them. These spores can be carried by rain and wind landing on developing fruit on nearby trees. 

The good news is that once the green berries appear, the chances of this disease developing reduce significantly.

Solution

Botrytis blight depends on high humidity and warmth. Frequent irrigation can lead to the development of this disease in your blueberry crop. One to two inches of water weekly is sufficient for your blueberry bushes to thrive. 

They also need soil that drains appropriately to keep healthy and strong. It would help if you also used fungicides to eradicate the disease, and the best option is broad-spectrum protectant fungicides.

Mid Development Browning

Frost Damage

Temperatures of below 28°F (-2°C) are low enough to cause freeze injury to some blueberry blossoms. However, the level of freeze injury depends on the developmental stage of the plant ranging from flower buds to young fruits.

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Between 20 and 30°F (-7 and -1°C), flower buds can survive and remain undamaged by frost. However, they will incur a high level of damage when temperatures remain the same as they emerge from the bud. This is because as the flowers begin to swell and the corollas emerge from the bud, their tolerance to cold temperatures decreases.

When the corollas are at their halfway length, temperatures below 26 to 30°F (-3 to -1°C) completely kill the blossoms depending on the variety. With frost damage, the blooms turn brown and die, but they remain attached to the stem. 

Bees, which are the primary pollinators of blueberry bushes, tend to avoid bushes with such flowers hanging off them. As a result, undamaged flowers on the same bush do not get pollinated and end up dropping rather than developing fruit.

Flowers that have completely opened are damaged when exposed to temperatures of 27°F (-3°C) and below, even for a few minutes. That is because the period just after the corollas fall and right before the berry starts to swell is extremely sensitive. Unfortunately, frost damage is not always evident until you see the brownish water-soaked flower that eventually withers and falls off.

Solution

Use nursery foam to cover the blueberry bushes and keep the cold out. They can provide up to 10°F (-12°C) of protection if you install it as a double layer. Nursery foam and row covers can be bought at gardening supply stores.

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Sprinkler irrigation is a great way to work the frost out of the crop. The water coats the crop, allowing you to control the temperature of the berries to the optimal level.

Post Pollination Browning  

Anthracnose Blossom Blight

Anthracnose Blossom Blight causes the flowers on the blueberry to brown, and then a salmon-colored oozing substance covers them. This disease is caused by Colletotrichum acutatum fungus and the plant can remain symptomless until the fruit is harvested. 

Unfortunately, the fruit will have rot when it ripens, earning the disease the name ripe rot.

When the blueberry plant is affected by this disease, you will notice lesions and sunken spots on the flowers of the blueberry, as well as the leaves and stems. The brown spots on the flower soon expand and cover it completely. As the infected parts darken, the blossoms eventually fall off. The lesions on the leaves and stem cause defoliation.

Solution

Spray your brushes with adjuvants and fungicides when the flower is still a late pink bud and not during full bloom. Phosphite fungicides have excellent efficacy against Anthracnose blossom blight.

Water-Related Browning

A blueberry bush that doesn’t receive adequate levels of water will begin browning on the leaves. As the drought continues, the browning spreads to the stem of the plant, which is unable to sustain healthy blossoms. The result is the browning of the flowers as they die and fall off because they do not receive enough nutrients.

It is essential to keep your plants well-watered with a thorough soaking in the dry summer months to avoid having stressed plants. However, you should maintain a watering schedule so that you do not also end up overwatering the plant. It is truly a delicate balance.

Solution

Of course, the first and typical reaction is always to make sure that you water your blueberry bushes sufficiently. However, if your plants are severely affected by a natural drought, some experts from Michigan State University believe that it is better to let them die back. As they die back and lose more leaves and stems, the remaining stems and leaves can be sustained by the low reserves of water in the ground.

Cutting down the bushes in the height of summer will cause the plants to produce new shoots even with limited water and food reserves. The resulting shoots are not going to be healthy as the plant can’t thrive on such little reserves. By winter, they will not be able to survive problems like frost damage.

Final Thoughts

During the first two years, your blueberry plant will produce an adequate number of flowers and fruits. However, it is best to pinch the flowers and fruits off such immature plants to allow them to establish strong roots. Allowing the plant to mature prevents:

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  • Poor growth patterns
  • Weak plants that are less tolerant of less than ideal environments
  • Vulnerability to common diseases
  • Limited productivity resulting in large clusters of flowers that become berries
  • Harvests that eventually get ripe rot

The good news is that the blueberry is not a high maintenance plant. By paying attention to these issues highlighted above, you can enjoy a healthy and vibrant bush producing a robust harvest for decades. Gardeners who allow their blueberry plants to have a strong start you can harvest from it for even up to 50 years.