Blossom End Rot (BER) is one of the most common physiological disorders that can be encountered in tomato cultivation, even in home gardening. Unfortunately, this issue renders the plant’s fruits unsellable due to their compromised quality.
After extensively discussing the main diseases to which tomatoes are susceptible, such as downy mildew and bronzing virus, as well as the most formidable pests like tomato leafminer and stink bugs, we now delve into the realm of physiological disorders, specifically discussing blossom end rot.
Let’s explore its agronomic causes and understand how to manage cultivation to prevent the issue. Most importantly, let’s discover how to organically correct the imbalances that lead to the dreaded black bottom on our fruits.
What is Blossom End Rot in Tomatoes?
Blossom end rot in tomatoes is a physiological disorder caused by abiotic factors, i.e., conditions that cause stress to the plants. This stress leads to morphological or color-related malformations in the fruit. Typically, the damage appears as a lesion at the blossom end of the berry (distal end). The color of the affected area varies from gray to black. Initially, the affected area of the tomato takes on a dull appearance (grayish). It then becomes necrotic and turns intensely black in color.
In the advanced stage of the disorder, the affected area becomes depressed and leathery. Generally, tomatoes damaged by blossom end rot ripen earlier than healthy fruits.
What Causes this Physiological Disorder?
During the warm months of June and July, which are the periods of vigorous plant growth, blossom end rot in tomatoes is more likely to occur.
The primary cause is a deficiency of calcium (Ca), a crucial element for healthy and balanced plant growth. The deficiency, which can sometimes result from simple scarcity in the soil, is often attributed to a problem of water stress in cultivation. For example, temporary water deficiency prompts the plant to rapidly withdraw water from the fruits, thus interfering with calcium transport. Since the fruits lack stomata and therefore transpiration activity, they succumb. Other vegetative organs, on the other hand, remain healthy as they are predisposed to water exchange.
Calcium is transported in the tomato plant along with water in the evapotranspirational flow. For this reason, it accumulates in areas with a higher density of stomata, i.e., the leaves, at the expense of the fruits.
Environmental conditions that favor rot are high temperatures and low humidity. These conditions divert water, and therefore calcium, towards the leaf tissue.
In agricultural practice, blossom end rot frequently occurs in soils that are susceptible to sudden variations in water regimes.
Other conditions that contribute to the onset of this disorder include:
- Calcium-deficient soils
- High soil salinity
- Excessive nitrogen fertilization
- Various root system damages, such as from nematodes, or lymphatic, like accidental stem wounds.
Tomato Varieties Most Affected
Among the various tomato varieties, some are more susceptible to blossom end rot. One such variety is San Marzano, which has a distinct elongated shape. Heart-shaped varieties are also more prone to this disorder, as are small-sized tomatoes. Medium to large round smooth varieties, however, tend to be less affected.
Preventing Tomato Blossom End Rot
As mentioned, water stress is at the core of the occurrence of this blossom end rot. Proper irrigation management is essential for prevention. It’s crucial to avoid water stagnation, which limits water penetration into the deeper soil layers. Good soil preparation helps in this regard by improving drainage.
Another necessary measure is to water the plants regularly. Essentially, it’s important to avoid both overwatering and drought periods. The principle is to water a little and often.
For this reason, when starting a tomato cultivation, it’s best to prefer a drip irrigation system. This method allows for a more even and controlled water distribution, making it preferable over overhead or sprinkler irrigation systems.
To improve soil moisture and reduce evaporation, natural mulching comes to the rescue.
To prevent tomato blossom end rot, a proper base fertilization of the soil is necessary. This ensures the presence of all the elements required for healthy and lush growth in the soil and thus available to the plant. Ideally, a substantial amount of organic matter, typically manure, should be incorporated into the soil during preparation. The use of home compost can also serve this purpose.
Base fertilization might not be sufficient when cultivating in soils severely lacking in calcium. By observing the youngest leaves of the plants, we can easily identify a deficiency of this element. In deficient soils, yellowing of leaves, especially the younger ones, will be noticeable.
In such cases, we can address the issue with top-dressing fertilization, using calcium-based fertilizers permitted in organic farming. Excellent products can be ordered here.
Foliar applications are also highly effective for calcium deficiencies, using organic-based products. A prime example is lithothamnium, a natural calcareous powder derived from marine sources, containing essential elements to counteract blossom end rot. It contains the aforementioned calcium, as well as boron and magnesium.
If you decide to use such products, we recommend adhering to the specific instructions provided by the manufacturers regarding dosages and application methods.
If you prefer not to purchase specific fertilizers and wish to address the issue domestically, you can use crushed eggshells. These can be buried near the plant or spread directly onto the soil. Eggshells contain a high amount of calcium, and their degradation gradually releases it for plant uptake.
Naturally, whatever strategy you choose, it’s best not to wait for the occurrence of the disorder before intervening, but rather to take preventive measures in advance.
One final agronomic technique to prevent tomato blossom end rot is direct intervention on the plant.
Firstly, it’s important to periodically prune the plant, following the usual pruning practices. For tomatoes, remove suckers (which can be used to make excellent organic insecticide), yellowing leaves under the flower cluster, and, in general, avoid an excessive number of leaves relative to the fruit load.
Another measure is not to remove tomatoes affected by blossom end rot immediately but allow them to ripen completely. Even if they are destined for compost rather than consumption, leaving them on the plant spreads the disorder to the already affected fruit while preserving new ones.
- MDPI: “Effects of Ca Sprays on Fruit Ca Content and Yield of Tomato Variety Susceptible to Blossom-End Rot” – The research investigates the role of calcium sprays in influencing the calcium content in tomato fruits, particularly in varieties susceptible to blossom-end rot.
- Horticulturae: “Modifying Walk-In Tunnels through Solar Energy, Fogging, and Evaporative Cooling to Mitigate Heat Stress on Tomato” – The article discusses the modifications in walk-in tunnels using solar energy, fogging, and evaporative cooling to reduce heat stress on tomatoes.
- Agronomy: “Tomato Disease Monitoring System Using Modular Extendable Mobile Robot for Greenhouses: Automatically Reporting Locations of Diseased Tomatoes” – This study introduces a modular extendable mobile robot designed for greenhouses to automatically detect and report the locations of diseased tomatoes.
- Plants: “Productive and Physico-Chemical Parameters of Tomato Fruits Submitted to Fertigation Doses with Water Treated with Very Low-Frequency Electromagnetic Resonance Fields” – The research delves into the effects of fertigation doses using water treated with very low-frequency electromagnetic resonance fields on the productivity and physico-chemical parameters of tomato fruits.
- Agronomy: “Mitigation of Calcium-Related Disorders in Soilless Production Systems” – The article discusses the challenges and solutions related to calcium-related disorders in soilless production systems, emphasizing the importance of calcium in preventing blossom-end rot in tomatoes.
- Iowa State University: “Blossom-end Rot of Tomatoes” – This article explains the causes and prevention methods for blossom-end rot in tomatoes, emphasizing the role of calcium and consistent moisture
- Missouri Botanical Garden: “Blossom-end rot of tomatoes and peppers”.