Blossom End Rot

These are some of the longest, hottest days of summer for many in the Midwest.  This can indicate longs days scouting and spraying crops, at the lake or family vacations.  As a delicious bonus it could mean maturing produce in the garden or harvest being sent to farmers’ markets/consumers.  As tomatoes, peppers, squash and melons are being harvested an annual recurrence of blossom end rot seems to still trouble some producers.

The first observation of this phenomenon is a soft, bruised spot on the bottom parts of the fruits.  Although it may seem like a disease, blossom end rot is a physiological disorder.  The bottom part of the fruit may start to look watery, soft and then turn dark brown to black.  It often creates the perfect environment to host bacterial and fungal diseases depending on temperature, humidity etc. leading to continued decay potentially consuming most of the fruit.

This type of rot is caused by lack of calcium in the fruit itself.  The first step is to make sure there is adequate calcium in the soil.  A simple soil test will be able to determine what the soil needs prior to the growing season, or even in-season depending on the grower’s preference of application practices and products.  Then the plants used need to be planted, or sowed, at the correct location, depth and spacing depending on the cultivar’s needs.  Low calcium levels in the fruit are often caused by inconsistent watering practices or lack thereof.  This nutrient is taken up by the plant by roots through the soil solution. 

If there is inconsistent moisture, poor root development or inadequate calcium in the soil solution blossom end rot is bound to happen.  Another consideration for this occurrence is how calcium is distributed through the plant.  Calcium is not a mobile nutrient in plants.  Once it is taken into plant tissues, it is not redistributed to other parts of the plant.  Its initial uptake is due to transpiration which leaves evaporate more water making them a large pool for calcium compared to fruit.  Too much vegetation, possibly from over fertilization of nitrogen, can also cause these large pools of calcium in the leaves rather than the fruit. 

If soil calcium is low, and this is the cause of blossom end rot, there are a few practices to consider going forward.  When the first fruit set is occurring, and rot is just showing, a liquid calcium product may be the answer for a quicker response time.  The finer the calcium product, the quicker it will become part of the soil solution. 

The long-term solution is adjusting the soil pH, and calcium levels based on a soil test recommendation.  Contradictory to quick uptake, the larger the particle size will result in long term adjustments. Timely, consistent watering and mulching the crops can keep the soil solution available to the plant roots and allow reliable uptake of calcium.