From: dmiller@theory.lcs.mit.edu (Dick and Jill Miller)
Newsgroups: rec.gardens
Subject: Blossom End Rot
Date: 26 Aug 92 11:58:06 GMT
Organization: Laboratory for Computer Science, MIT

With all the discussion about blossom end rot lately, I thought I'd send 
along this paper from the Cornell Cooperative Extension.

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Blossom End Rot

Blossom end rot is a physiological disorder that is caused by a lack of 
calcium uptake from the soil and transfer to the fruits during dry weather.  
The problem is costly to many tomato growers and disappointing to home 
gardeners.  Peppers can also be affected.  The disorder, however, is less 
common on peppers.  Research in Florida indicates that excessive magnesium, 
potassium, sodium, or ammonium salts, or a deficiency of soluble calcium 
salts, cause a decrease in calcium uptake thus favor development of the 
disorder.  Rapid early growth accentuates the problem because it tends to 
increase the calcium requirement per unit of time.

The first symptom of rot is a slight water-soaked area near the blossom end 
of the fruit.  The lesion soon darkens and enlarges in a constantly 
widening circle until the fruit begins to ripen.  The decaying spot may be 
merely a speck or it may involve half or even more of the tomato.  
Secondary fungi may inhabit the black area.  Although a sudden lack of 
water is the principal cause of blossom end rot, excessive soil moisture 
early in the season may smother the root hars and cause blossom end rot to 
occur during sudden hot weather.  It may be more serious on the windward 
than on the leeward side of a field and more common on staked tomatoes 
than on bush types.  Generally, blossom end rot is most common on the first 
fruits to turn red.

Management:  Since blossom end rot is so closely related to adaquacy of the 
water supply, an important control is to regulate the moisture supply in 
the soil.  The land should allow good drainage during a wet period.  If 
drought occurs, cultivation should be very shallow to reduce water loss and 
irrigation should be used.  Hoeing or cultivation should be performed no 
closer than one foot from the plants to reduce root pruning.  Appropriate 
amounts of fertilizer high in superphosphate and low in nitrogen should be 
used (1-3-1 ratio).

In the greenhouse, transplants should not be grown too quickly nor should 
the plants be too old and subjected to severe hardening before 
transplanting.  A steady growth rate as a seedling and as a field plant 
will discourage much of this trouble.

If irrigation of any kind is available, it should be used during periods of 
hot, drying winds.  Start to irrigate at the beginning of the dry spell.  
Mulching, which serves to maintain an even level of soil moisture, should 
be practiced where feasible.  Mulch with black plastic or grass clippings 
to reduce moisture loss and to control weeds.  Tomatoes and peppers planted 
unusually early, while the soil is still cold, are likely to have the first 
fruits affected by blossom end rot.  Consequently, a delay in planting 
until soils warm up helps to reduce the problem.

The tomato varieties Jet Star, Burpee VF, Better Boy, Early Girl, 
Flora-Date, Floramerica and Walter seem to have some tolerance.

7/72 Prepared by:       Arden F. Sherf
                        Department of Plant Pathology
3/91 Revised by:        Diane M. Karasevicz
                        Extension Associate


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