Blossom end rot is a disorder in which spots appear on the blossom ends of fruits. These spots are initially brown or yellow in color, and wet to the touch. Over time, these spots turn rotten, taking on a leathery black appearance. Blossom end rot is not caused by viral or bacterial infections, or pest infestations, but rather is a product of nutritional imbalances and water stresses.
Blossom end rot is easily identified by the telltale rotten spots on the bottoms/ends of affected tomatoes, peppers, and other affected fruits.
The first sign of blossom end rot usually appears as a light-colored yellow or tan patch on the blossom end of the fruit. As the fruit develops, this patch will spread, darken, and become sunken. Early on, these patches are soaking wet, but eventually dry out and become black. In more minor cases, spots remain small and present as a cosmetic imperfection. But in more serious instances, the rotten region will encompass a third to one-half of the surface area of the fruit.
Regardless of severity, symptoms of blossom end rot start and are contained to the blossom ends of fruit (hence the name). However, blossom rot can leave fruits extremely vulnerable to secondary infection by pathogens. When this occurs, the entirety of affected fruits can rot.
Parts of fruits not affected by blossom rot can be safely eaten, and blossom end rot does not impact the overall health of plants. However, the appearance of affected fruit are so unsightly that they are often unsellable.
Blossom end rot is not a fungal, viral, or bacterial disease. It’s a product of nutritional deficiencies and/or poor water management.
The core issue contributing to blossom end rot is a calcium deficiency. But oftentimes, calcium levels in the soil are more than sufficient. This is why growers who respond to the early of blossom end rot with applications of calcium are rarely successful in staving off the disease. Instead, there is an issue with the delivery of calcium to where it is needed.
Blossom end rot is the consequence of a cascade of issues, usually starting with inconsistent moisture levels during the critical period when fruits are going through a period of rapid growth early in the growing season. At the point where fruits are about one-third to one-half their full size, they are extremely vulnerable to water stress.
When moisture levels in the soil vary, with repeated instances of drought, water will tend to be sent to the leaves of the plant, rather than the fruit. Transpiration—the movement of water into the leaves and stems, where it then evaporates—is critical to both temperature regulation within the plant, as well as the absorption of carbon dioxide.
Both leaves and fruit are capable of transpiration, but the rate of transpiration occurs more rapidly and readily in leaves than in fruit. This is in large part because leaves have a much greater ratio of surface area to tissue volume. Thus, when temperatures are high and moisture levels are low, water is drawn preferentially to the leaves, and away from fruit. This disparity becomes more pronounced when fruits develop a waxy cuticle, as this further slows the rate of transpiration.
Water is the chief means by which calcium is transported through a plant. When fruits are starved of moisture, they are also starved of calcium. Calcium is critical in the development of strong cell walls, and this is especially so in the rapid growth phase of fruits.
The consequence of inadequate water and calcium delivery is that while the side of the fruit nearest the stem gets enough calcium to form rugged tissues, the blossom end is deficient in calcium, and the plant tissue breaks down. The result is the eponymous blossom end rot.
Blossom end rot can also be exacerbated by excessive applications of nitrogen, as this stimulates the growth of leaves. Larger leaves have a greater demand for water, and thus deprive the fruit of moisture. Cool weather can also reduce water uptake, which is why blossom end rot is often seen in early plantings of tomatoes.
Controlling blossom end rot requires the improved management of moisture levels in soil and taking steps to ensure maximum calcium uptake.
The easiest way to keep soil moisture levels consistent is applying several inches of mulch to fields, as this will help to hold in moisture. When periods of hot weather are expected, increase irrigation several days beforehand. Applications of Fusion 360 Foliar FG-31 are advisable as well. FG-31 supplies a balanced mix of calcium and other nutrients specially designed to enhance mineral uptake and nutrient absorption during periods of stress, including the heat/water-stress conditions which lead to blossom end rot.
Steps should also be taken to avoid excessive applications of nitrogen. Adopting a balanced nutritional program that provides balanced levels of calcium and boron—both critical in the development of stable plant tissues—will make crops more resistant to blossom end rot.
In soil conditions where mineral and nutrient tie-up is often an issue—which can lead growers down the path of excessive nitrogen applications that create conditions ripe for blossom end rot—we also recommend the use of Fusion 360 Soil, Keel 0-0-1, and Iota 0-0-1. Fusion 360 Soil reduces mineral tie-up and enhances the bioavailability of fertilizers, while Keel 0-0-1 optimizes the effectiveness of multi-nutrient fertilizers by reducing the rate of precipitation and other reactions which have a negative impact on solubility and availability of nutrients. Lastly, Iota 0-0-1 is specially designed to improve soil conditions where water infiltration issues are a concern.
In addition to the above, where possible, holding off on early spring plantings until soil temperatures have warmed will also reduce the incidence of blossom end rot.
If after adopting the above practices, you still struggle with blossom end rot, have a soil pH test performed—a pH of 6.5 to 7 maximizes the uptake of calcium relative to other minerals. As always, you should also ensure that soil calcium levels are adequate. Supplement as necessary.