Posted: August 18, 2012
No bacteria or pest causes blossom-end rot, rather the plant cannot get what it needs: calcium. This disorder is caused by a lack of calcium uptake from the soil and resulting in little transfer to the fruits during dry weather. Because we have experienced a much lower rainfall this season, you may be seeing the signs of this now.
Symptoms may occur at any stage in the development of the fruit, but most commonly are first seen when the fruit is one-third to one-half its full size. As the name of the disease implies, symptoms appear only at the blossom end of the fruit. Initially a small, water-soaked spot appears, which enlarges and darkens rapidly as the fruit develops. The spot may enlarge until it covers as much as one third to one-half of the entire fruit surface, or the spot may remain small and superficial. Large lesions soon dry out and become flattened, black, and leathery in appearance and texture.
Blossom-end rot happens when a number of conditions come into place. The disease is especially prevalent when rapidly growing, succulent plants are exposed suddenly to a period of drought. The roots fail to obtain sufficient water for calcium to be transported up to the rapidly developing fruit, causing the bottom of the tomato to rot. Other factors include a pH out of range and damage done to the roots from cultivation too closely. Soils that contain excessive amounts of soluble salts may predispose tomatoes to the disease, for the availability of calcium to the plants decreases rapidly as total salts in the soil increase.
To manage blossom-end rot take these steps:
• Water consistently if there is a lack of rain, about one inch per week.
• Add mulch to your garden, this conserves moisture.
• Use fertilizer low in nitrogen, but high in superphosphate, such as 4-12-4 or 5-20-5
• Do not spray any type of pesticide, as this is not a symptom of insect, bacteria, or fungi damage. Pesticides are ineffective on blossom-end rot.
• Consider a soil test. This will give you a complete analysis of what your garden needs and will give you a head start for the next growing season.
For more information on blossom-end rot, contact the Penn State Master Gardener Helpline at 570-963-6842, or email us at LackawannaMG@psu.edu and request a free copy of the blossom-end rot publication.
Master Gardener Coordinator
Penn State Cooperative Extension in Lackawanna County