It is believed that both nutritional and environmental factors need to be considered when diagnosing and recommending treatments.

 

Calcium serves several functions in plants, including cation-anion balance, transport processes of cell membranes and assisting with extension of primary root systems. For vegetable producers, calcium’s most important function during the crop fruiting stage is its role in cell wall/cell membrane stability. If Ca is deficient in developing fruits, an irreversible condition known as blossom-end rot (BER) will develop. Blossom-end rot occurs when cell wall calcium “concrete” is deficient during early fruit development, and results in cell wall membrane collapse and the appearance of dark, sunken pits at the blossom end of fruit. Many farmers and gardeners may treat this condition as a fruit disease; however, nutrient and water management regimes are the culprit.

 

 

 

 

 

 

 

 

 

 

Four simple questions in the field will lead to a timely diagnosis and treatment of the problem:

 

Is the problem disease- or nutrient-related?

 

There are only a few common fruit disorders resembling BER that can lead to an incorrect diagnosis of the problem. Fruit anthracnose may occur on  tomato fruit, but only on the side walls. The same is true for sunscald, which appears on  fruit sidewalls and is pale in color.

 

 

 

 

 

 

 

 

 

 

Buckeye rot, caused by Phytophthora, and cucumber mosaic virus (CMV) also resemble BER, but these disorders occur more infrequently than anthracnose. Blossom-end rot is uniformly dark brown and black in color, and appears ONLY on either the lower fruit sidewall or the blossom end of smaller and developing fruit. Often, symptoms will occur as far as 1/3 to halfway up the fruit, but will NEVER start at the stem (calyx) end. Also, BER symptoms will tend to appear during the first fruit set as, early on, growers are unaware of the problem until it’s too late. If these symptoms all correspond, the fruit has BER 

 

Recommendation: If these conditions all hold true, then check for calcium fertilization adequacy.

 

Is calcium fertilization adequate

 

• Examine liming and gypsum application records, along with the current season’s pre-plant soil test reports. If pre-plant soil test Ca levels are in the medium (801 to 1,200 lbs. Ca/acre) or high range (>1,200 lbs. Ca/acre), it is assumed that soil Ca levels are sufficient for crop growth. This is even more true for soil pH ≥ 6.0, with supplemental gypsum or lime being applied pre-plant at levels of 500 to 1,000 lbs./acre or higher.

 

If these conditions exist, then check for nitrogen and potassium fertilization levels.

 

Further, equally important to soil test is plant tissue analysis. For tomatoes, percent Ca content prior to (or at) early bloom should be within the range of 1.25 to 3.20 percent. Tissue levels below these would point to a possible emerging Ca deficiency.

Recommendation: No specific recommendations exist for alleviating a low soil Ca level after planting. However, calcium nitrate (CaNO3) is a water soluble source of Ca and nitrogen (N) and is routinely injected in drip irrigation systems. Calcium thiosulfate (CaS2O3), is also available for drip injection systems. Injections of soluble Ca sources should begin at bloom and proceed until fruit is approximately golf ball-sized. This is believed to be the critical time when calcium must move into developing fruit to avoid onset of BER.

 

Although some people believe foliar sprays can correct Ca deficiency in developing fruits, research is very inconclusive on this issue. What is well known is that Ca only moves in the plant via the xylem and moves with the transpirational water flow from the roots, up the plant and into developing leaves. Calcium has no ability to flow from the leaves via the phloem to the developing fruit. In addition, once fruit has grown to golf ball size, the waxy outer layer has developed and is believed to be quite impermeable to water. Therefore, it is recommended that all Ca supplied to fruiting vegetables be applied via the irrigation water so as to maximize uptake by roots. 

 

If liquid fertilizers are already being used, then check for nitrogen and potassium fertilization levels.

 

Is nitrogen and potassium fertilization excessive?

 

• Research has shown that Ca in soil solution competes with potassium (K), magnesium (Mg) and ammonium-nitrogen (NH4-N) for uptake in the plant. Excessive shoo

• t growth resulting from overfertilization of N and K during early bloom and fruiting stages is a major contributor to BER in developing fruit. Since Ca moves with the transpirational water flow, water is going to go to areas of new shoot growth that have the greatest transpirational demand. Calcium will therefore be deposited in the new shoot and leaf tissues that result from excess fertilization, and little will end up in developing fruit where it is needed most. At early bloom stage for tomato, leaf N and K analysis should both be within 4.0 to 6.0 percent. Levels higher than these may indicate excess fertilizer.

 

Recommendation: Cut rates of N and K if excessive top growth is occurring. Switch N source to CaNO3 or begin injections of CaS2O3 at bloom stage. 

 

If these steps are already being implemented, then check for adequate irrigation

 

• Fluctuations of soil moisture, as happens during a week of off-and-on rain, may trigger BER due to irregular transpiration rates, affecting the quantities and timing of water and Ca moving up the xylem. Conversely, during hot, dry weather when transpiration is occurring at a much faster rate, developing vegetative parts such as growing leaves and stems become greater sinks for Ca than developing fruits. Lastly, as the waxy outer layer of a tomato fruit develops, the fruit’s  transpiration rate decreases because water movement through the epidermal cells and evaporation into the outside air become difficult. The resulting decrease of Ca that flows into those young fruit tissues via xylem transport is believed to contribute to the onset of BER.

 

Recommendation: Some research findings have quantified a decrease of BER incidence with increased irrigation rates. However, no recommendations exist for determining the critical moisture levels required in soils to minimize this disorder, nor is information available regarding the severity of moisture deficits triggering BER.

 

Assessing soil moisture in the field

 

The “feel” method is still the most tried and true method of assessing soil moisture in the field. Along the row and out to the shoulders of the bed, the soil should be moist enough to form a ball in your hand and not break apart. The optimal time to increase irrigation and ensure that adequate moisture is being supplied is from first bloom set through fruit development. If BER initiates in fruit, it is believed to be during this early stage of development.

Certain occasions exist where farmers run irrigation pumps “round the clock” and soil still will not form and hold a good ball shape. This may indicate that irrigation demand during the fruiting period is greater than that for which the pumping system was designed.