Posts Tagged ‘blossom end rot’

Hot Year Means More Blossom End Rot

Friday, July 20th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Blossom end rot (BER) is showing up again this year in peppers and tomatoes. BER is a disorder where developing fruits do not have enough calcium for cell walls, cells do not form properly, and the fruit tissue at the blossom end collapses, turning dark in color. Calcium moves through cation exchange with water movement in the fruit, so the end of the fruit will be the last to accumulate calcium. Larger fruits and longer fruits are most susceptible. With fruits, the rapid cell division phase occurs early in the development of the fruit and if calcium accumulation in the fruit is inadequate during this period, BER may occur. While it may not be noticed until the fruit expands, the deficiency has already occurred and cells have already been negatively affected. We most commonly see signs of blossom end rot on fruits many days after the calcium deficiency has occurred.

Understanding blossom end rot also requires an understanding of how calcium moves from the soil into and through the plant. Calcium moves from the soil exchange sites into soil water and to plant roots by diffusion and mass flow. At plant roots, the calcium moves into the xylem (water conducting vessels), mostly from the area right behind root tips. In the xylem, calcium moves with the transpirational flow, the movement of water from roots, up the xylem, and out the leave through stomata. Calcium is taken up by the plant as a divalent cation, which means it has a charge of +2. It is attracted to negatively charged areas on the wall of the xylem, and for calcium to move, it must be exchanged off the xylem wall by other positively charged cations such as magnesium (Mg++), potassium (K+), ammonium (NH4+), or additional calcium cations (Ca++). This cation exchange of calcium in the xylem requires continuous movement of water into and up through the plant. It also requires a continuous supply of calcium from the soil.

In general, most soils have sufficient calcium to support proper plant growth. While proper liming will insure there is adequate calcium, it is not the lack of calcium in the soil that causes blossom end rot in most cases. It is the inadequate movement of calcium into plants that is the common culprit. Anything that impacts root activity or effectiveness will limit calcium uptake. This would include dry soils, saturated soils (low oxygen limits root function), compaction, root pathogens, or root insect damage. In hot weather on black plastic mulch, roots can also be affected by high bed temperatures. Low pH can also be a contributing factor. Calcium availability decreases as pH drops, and below a pH of 5.2 free aluminum is released, directly interfering with calcium uptake. Again, proper liming will insure that this does not occur. Applying additional calcium as a soil amendment, above what is needed by normal liming, will not reduce blossom end rot.

In the plant, there is a “competition” for calcium by various plant parts that require calcium such as newly forming leaves and newly forming fruits. Those areas that transpire the most will receive more calcium. In general, fruits have much lower transpiration than leaves. In hot weather, transpiration increases through the leaves and fruits receive lower amounts of calcium. High humidity will reduce calcium movement into the fruit even more. Tissue tests will often show adequate levels of calcium in leaf samples; however, fruits may not be receiving adequate calcium. In addition, in hot weather, there is an increased risk of interruptions in water uptake, evidenced by plant wilting, when transpirational demand exceeds water uptake. When plants wilt, calcium uptake will be severely restricted. Therefore, excess heat and interruptions in the supply of water (inadequate irrigation and/or rainfall) will have a large impact on the potential for blossom end rot to occur. Proper irrigation is therefore critical to manage blossom end rot.

As a positive cation, there is “competition” for uptake of calcium with other positive cations. Therefore, if potassium, ammonium, or magnesium levels are too high in relation to calcium, they can reduce calcium uptake. To manage this, do not over-fertilize with potassium or magnesium and replace ammonium or urea sources of nitrogen with nitrate sources.

Applying additional soluble calcium through irrigation, especially drip systems, can reduce blossom end rot to some degree if applied prior to and through heat events and if irrigation is applied evenly in adequate amounts. Foliar applications are much less effective because fruits do not absorb much calcium, especially once a waxy layer has developed, and calcium will not move from leaves into the fruit (there is little or no phloem transport).

In conclusion, the keys to controlling blossom end rot are making sure roots are actively growing and root systems are not compromised, soil pH is in the proper range, and irrigation is supplied in an even manner so that calcium uptake is not interrupted. Supplemental calcium fertilization will only marginally reduce blossom end rot if water is not managed properly.

Another calcium disorder that is found in peppers is called “stip”. These spots on peppers occur later in the year, commonly in the late summer or fall, during cool, humid conditions. Under these conditions, calcium movement into the fruit is uneven, leading to localized collapse of cells, causing the spotting. Again, making sure adequate calcium is moving in the plant is critical to control stip.

Pruning Tomatoes

Friday, June 8th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Commercial determinate tomatoes may require pruning of “suckers”, those shoots that develop at lower nodes. Removal of one or more of these shoots up to the first fork, just below the first flower cluster, can improve fruit size, quality, and marketable yield on some varieties. Varieties that are very vigorous and tall with a lot of foliage such as BHN589 are the best candidates for pruning. Pruning will increase fruit size, increase early set, and reduce disease pressure by improving air movement and spray coverage. However, fruit numbers will be reduced. Pruning is best carried out prior to first stringing when shoots are small (2 to 4 inches long). They can be removed by bending the shoot backward where it easily snaps off. Later pruning with larger shoots may require the use of hand pruners to avoid excessive tearing. A second trip through the field after stringing may be required to remove late developing suckers. Always prune when foliage is dry to avoid spreading diseases. The amount of pruning required will vary by variety. Some varieties require little or no pruning or removal of ground suckers only (those coming from the cotyledon node); vigorous varieties may require the removal of ground suckers plus two additional suckers. Check with your seed-persons for pruning recommendations for the varieties you are using. Over-pruning can result in reduced yields and increased sunburn, blossom end rot, fruit cracking, and catfacing.

Hot Weather and Blossom End Rot

Friday, June 17th, 2011

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The extreme heat that just recently ended was exceptionally stressful on plants, especially newly transplanted plants. But even well established plants found in high tunnels or that were planted early in the year were stressed. Tomato plants in a high tunnel I visited had severe blossom end rot problems that are just now becoming apparent. Usually with blossom end rot you get a few tomato fruit that are all of one general size scattered about on plants. This shows that calcium uptake was deficient just as the fruit was developing. Tomato fruit that reaches the size of a dime usually has all the calcium it is going to need and if it does not the cells of the fruit furthest from the stem do not develop normally and collapse as the cells and fruit expands causing blossom end rot. Calcium (Ca) moves to the plant via mass flow, i.e., where dissolved minerals like calcium move to the root in soil water that is flowing towards the roots. If anything interrupts this constant flow calcium deficiency can occur in developing fruit. For different sized fruit to develop blossom end rot there must have been an extended disruption in calcium uptake. This can be seen in figure 1 where several different size fruit all have developed blossom end rot. Figure 2 shows that large fruit on this particular plant developed before there was a Ca interruption, but the fruit a little younger suffered the hot weather induced Ca interruption, with the smallest, youngest fruit suffering the greatest damage. Tissue analysis from this same set of plants showed that calcium was in the high range when the blossom end rot took place, demonstrating the importance of irrigation and water supply to reduce blossom end rot.

Fig. 1 Several fruit of different sizes with blossom end rot

Fig. 2 Older, larger fruit received enough Ca, but younger, smaller fruit did not

 

Blossom End Rot in Tomatoes

Friday, June 25th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

This is just a quick reminder that we are in very dry conditions right now and tomato plants are putting on large fruit at the same time they are flowering profusely. Everyone knows that blossom end rot is caused by too little calcium in the fruit while it is developing, usually from the time of flowering until it is the size of a quarter. Most of the blossom end rot I have seen in tomato is due to too little water supplied to tomatoes during dry, very hot periods like we are having now. Some varieties are much more sensitive to dry conditions and will show severe blossom end rot symptoms while other varieties do not. Your tomato plants are going to need more water than you may be used to giving them over the next few weeks if conditions remain hot and dry.


Blossom end rot on tomato fruit

Blossom End Rot in Tomatoes

Friday, July 24th, 2009

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Blossom end rot has appeared in tomatoes throughout Maryland in the last few weeks (Fig. 1). This is mostly due to the very dry conditions we have had this month. Blossom end rot is caused by too little calcium reaching the cells on the blossom end of the fruit as it is developing. Calcium is dissolved in soil water and is taken up by the plant through the vascular system. During periods of high moisture stress, water containing calcium moves rapidly through the plant to the leaves with most of the calcium ending up in the leaves after transpiration has occurred. Since the fruit transpires very little, less calcium is deposited there; resulting in a localized calcium deficiency in the fruit. Almost all of the calcium that a mature fruit needs is within the fruit when it is the size of a nickel.

Figure 1. Several different ‘forms’ of blossom end rot on tomatoes

blossom end rot on tomato fruit 

Therefore, the blossom end rot that appears on fruit that is about ready to be harvested had the critical period of inadequate calcium occur weeks earlier. Even a temporary water stress during early fruit enlargement can cause blossom end rot. Another cause of blossom end rot is over-fertilization, especially with nitrogen. The excess nitrogen stimulates vegetative growth, which increases the transpiration rate and further inhibits calcium accumulation in the fruit. Cultivars that grow quickly and produce large amounts of foliage tend to be more susceptible to blossom end rot. Therefore, reducing nitrogen levels will help reduce blossom end rot. The prevalence of blossom end rot also may be exacerbated when there is a low ratio of calcium to certain other nutrients such as potassium and nitrogen. About the only place where I have seen little blossom end rot on tomatoes is when they are in high tunnels where moisture levels can be more precisely controlled.