Growing Points: More on boron with peppers

December 12, 2013
Written by Dr. Mohyuddin Mirza
My writing on the subject of nutritional deficiencies this month has been triggered by an e-mail I received from an experienced pepper grower.

The problem? He did not know why his greenhouse peppers were showing strange symptoms on young fruit.

Here are the pictures that came with the e-mail. It is so good to see how fast it is to send pictures thanks to the availability of smartphones and other gadgets. Just snap the pictures and send them! Have a look at these crop photos.

 Boron-deficiency  
 Misshappened-pepper  

The grower did not report any leaf symptoms, although I suspect that there were symptoms of discoloration on them. 

My immediate reaction was that it was boron deficiency, but I wondered why it was happening at such a late crop stage.

I asked for an analysis of feed and leach solution.

I also learned this was a new greenhouse range with different quality water than the grower used previously. It was also a different fertilizer program than was being used in the other greenhouse.

An analysis of feed and leach solution showed boron levels of 0.26 ppm (24.03 µmoles) in feed and 0.35 ppm (31.44 µmoles). The recommended level is 45 to 75 µmoles in the leach. Peppers require higher levels of boron in the feed when compared to cucumbers and tomatoes. I recommend a target of 0.8 to 0.9 ppm in the feed.

WHAT DO WE KNOW ABOUT BORON
Boron deficiency is an occasional problem in pepper crops and the warning signs usually first appear in the leaves. The symptoms can appear despite reasonably high levels in the growing medium. The symptoms on leaves appear as a loss of colour of one quarter of the leaf, or sometimes the top half of the leaf shows a loss of colour.

At later stages, the leaves can also become “crinkled” or “puckered” as well.

 Advanced-boron-deficiency  
 Early-stage-of-boron  

Boron’s uptake is “passive,” meaning that active transpiration is required to move this element within the plant. It resembles calcium in that regard. Like calcium, it is “immobile,” meaning that if deficiency occurs at top of the plant, the lower leaves don’t transport it as is done in the case of nitrogen and potassium. Its uptake also depends on pH of the growing medium. Its availability is reduced with alkaline pH.

The top leaf picture on the facing page indicates how boron deficiency in peppers may look at an advanced level. These are generally upper leaves. As mentioned earlier, boron is immobile, meaning that once it is fixed in the cells it cannot be moved to upper leaves. The lower leaf picture is an illustration of boron deficiency in peppers at an early stage. Vein clearing is evident in this case.

Boron is involved in the metabolic processes in meristematic tissue and RNA formation. Its deficiency causes malformation of young tissue, as is shown in this case of peppers.

Root health and boron uptake: Root health is affected by many inputs, such as watering, oxygen status and nutrient content. However, pH plays the bigger role in the uptake of boron. It is taken up by young roots. Very high fruit load is also implicated in creating a deficiency of boron. A pH level going over 6.5 causes a reduced uptake of boron.

I have also seen root tips turn brown and die off resulting in more branching. Most of the time calcium and boron deficiencies are occurring together.

SOURCES OF BORON
The term “borax” is often used for a number of closely related minerals or chemical compounds that differ in their crystal water content. Growers must know what they are dealing with because the boron content will be different. Here are three examples of borax with different contents of water.

• Borax: Anhydrous borax
    (Na2B4O7).

• Borax pentahydrate
   (Na2B4O7·5H2O).

• Borax decahydrate               
   (Na2B4O7·10H2O).

Anhydrous borax will contain 21.39 per cent boron, borax pentahydrate will contain 14.8 per cent boron and borax decahydrate will contain 11.28 per cent boron. The amount you need for the same ppm concentration will vary depending on the type of borax used. 

CONCLUSIONS
  1. Peppers need higher boron levels in the feed solution and in the leach compared to other vegetable crops.
  2. Leaf symptoms provide an early indication of its deficiency.
  3. Root health and heavy fruit load can cause a temporary shortage in actively growing tissue.
  4. Boron is an immobile element and resembles calcium in this regard.
  5. Know the boron content in the borax you are using.

Dr. Mohyuddin Mirza is a greenhouse consultant. • This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Comments  

 
0 #1 Cliff Poy 2017-09-24 17:26
HI,
if my grow medium ph is high eg 7.3 to 7.5,
can I then apply a product that has both calcium and boron by foliar means ?
Thanks,
Cliff
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