The Hort Americas team shares insights and tips on how to prevent blossom end rot:

How to avoid blossom end rot

Blossom end rot can be a common problem for growers. This problem is characterized by the presence of necrotic tissue at the bottom of fruits such as tomatoes and peppers. The presence of necrotic tissue is caused by the lack of calcium in the buildup of new cells at the growing area of the fruit. Nutrient deficiency can be commonly linked directly to the nutrient solution recipe. However, it is crucial to understand calcium as a passive nutrient and how environmental conditions can trigger deficiency by affecting the ability of the plant to take up these minerals.                                   

There are several environmental conditions that can trigger calcium deficiency. The most common factors include:

Low relative humidity. When plants are exposed to low relative humidity levels, small pores in leaves called stomata close. Stomata are responsible for transpiration. Calcium movement depends entirely on stomata behavior. It is important to know the optimum relative humidity levels for each crop and to keep the humidity levels as uniform and consistent as possible. The humidity in a greenhouse can be increased by running water through the evaporative cooling pads and/or by installing a fog system if necessary. Blossom End Rot is characterized by the symptom shown by the fruit. However, leaves can also show a calcium deficiency. It is always important to make the proper observation when looking to fix calcium deficiency. This is because calcium deficiency when relative humidity is low will be noticed by problems on the fruit but also on the leaves. Leaves will present necrotic tissue in the growing area. 

High salt content at rootzone. When substrates accumulate salts, the plant receives a signal as water stress. This response can cause stomata to close, avoiding the movement of calcium to fruits and leaves. 

Lack of airflow over the crop. There needs to be air movement around the leaves to ensure continuous gas exchange. The airflow velocity around the plant leaves can be reduced as a result of the friction between the leaf surface and the moving air. This creates a boundary layer which is a layer of heavy air that can decrease gas exchange in plants. This reduction in gas exchange can impact calcium uptake by the plants. Lack of airflow can be linked to high humidity levels. This condition usually causes calcium deficiency in the fruit. 

High VPD levels. Some crops, including tomatoes, show tip burn under high VPD levels. Transpiration from roots to leaves increases under a high VPD environment. When VPD is too high for tomatoes, calcium uptake goes directly from the roots to the leaves, bypassing the fruit. This is why sometimes blossom end rot (calcium deficiency in fruit) occurs in tomato fruit, but no deficiency symptoms appear on the leaves.

Avoiding calcium deficiency
When calcium deficiency is seen in plants, make sure to check that the fertigation system is operating properly. If the fertilizer stock solution is maintained in multiple tanks, check all reservoirs to ensure the same solution levels so that all nutrients are being delivered uniformly to all crops.

Remember always to monitor environmental conditions before adding calcium to any crop. This includes removing or adding humidity to the greenhouse or increasing airflow. If calcium is added to the nutrient solution when calcium deficiency is promoted by the environment, you will be promoting Ca toxicity at the rootzone, which can end up causing other nutrient deficiencies in passive nutrients.

For more information: 
Chris Higgins, CEO
Hort Americas

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