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Steps to reduce blossom-end rot in tomato plants

Blossom-end rot is a disorder that results in the decay of tomato fruits on their blossom end.
Blossom-end rot is a disorder that results in the decay of tomato fruits on their blossom end. Photo provided

I recently received an email from Frank Koziol with some pictures of tomatoes from his garden. He was wondering if I knew what the problem was and could I help him out. I did indeed know what the problem was and thought that I would share the information with readers, in case you have seen the same problem in your tomatoes.

The problem that Frank was experiencing was blossom-end rot of his tomatoes, which is a physiological disorder usually caused by a lack of calcium in the blossom end of the tomato fruit and compounded by fluctuations in the water supply. Because calcium is not a highly “mobile” element in the plant, even brief changes in the water supply can cause blossom-end rot. Droughty soil or damage to the roots from excessive or improper cultivation — root pruning, for example — restricts water intake and can prevent plants from getting the calcium they need from the soil. This disorder results in the decay of tomato fruits on their blossom end. In the beginning you will notice dry brown or tan areas the size of a dime, which then grow to the size of a half dollar. This disorder is usually most severe following extremes in soil moisture (either too dry or too wet).

To reduce blossom-end rot in tomato, implement the following steps:

▪ Check the pH of your garden soil by taking a soil test. Kits are available from your local county extension office or for $9 from the Penn State Ag Analytical Services Laboratory, 111 Ag Analytical Services Lab, University Park, 863-0841.

▪ Lime tomato soils to pH 6.5 to 6.7. Home gardens not limed in the past two to three years will need 2 cups of lime for each plant. The lime should be worked into the soil 12 inches deep.

▪ Fertilize properly. Applying too much fertilizer at one time can result in blossom-end rot. Following soil test recommendations is the best way to ensure proper fertilization. For home gardens not soil tested, apply 5 pints of 8-8-8 per 100 feet of row, and thoroughly work it into the top 8 inches of soil.

▪ Mulch plants. Use organic materials such as straw, decomposed sawdust, ground/decomposed corncobs, plastic or newspapers. Mulches conserve moisture and reduce blossom-end rot. In extreme drought, plastic may increase blossom-end rot if plants are not watered. Using drip irrigation will help eliminate this problem.

▪ Irrigate when necessary. Tomato plants require about 1.5 inches of water per week during fruiting. This amount of water should be supplied by rain or irrigation. Extreme fluctuations in soil moisture result in a greater incidence of blossom-end rot.

▪ Spray calcium. The plants may be sprayed with a calcium solution using calcium nitrite or calcium nitrate or calcium chloride at 4 level tablespoons per gallon of water. Be careful with calcium chloride. If day temperatures are greater than 85-90 degrees Fahrenheit , calcium chloride can burn plants. Under high temperatures, use calcium nitrate. This spray should be applied 2 to 3 times a week, beginning at the time the second fruit clusters bloom. These materials can be mixed with the spray that is used for control of foliar diseases. Chelated calcium solutions also provide an excellent source of calcium. When using these chelates, follow label directions. Several foliar spray materials containing calcium are available and all work well for tomatoes.

If you experience severe problems with blossom-end rot, remove the infected fruits. Once a fruit develops blossom-end rot it will not re-grow or repair the infected area. Leaving the damaged fruit could serve as an entry point for disease-causing bacteria, fungi and insects.

Bill Lamont is a professor and extension vegetable specialist in the department of plant science at Penn State and can be reached by email at wlamont@psu.edu.