Iron Chlorosis is the most common micro-nutrient problem of fruits in New Mexico.  It is the result of the inability to extract sufficient iron from the soil, but not usually caused from a deficiency of iron.  New Mexico soils generally have plenty of iron especially in the red soil or red rock areas.  Iron is required to produce chlorophyll which in turn is what feeds the plant and promotes growth.  It appears as a yellowing of the leaf tissue between the veins.  In severe cases it will cause the leaves to turn a very pale yellow and possibly even white if it is past “severe”.  At first glance it can resemble a nitrogen deficiency but is distinguished in 2 ways.  With iron chlorosis the veins of the leaf will remain green. Nitrogen deficiency will turn all of the leaf yellow.  Also iron chlorosis starts with new leaves and nitrogen deficiencies first appear on the older leaves.

 The underlying cause is a high soil ph, which is what most New Mexico soils have.  Different plants and varieties within a species have different levels of tolerance.  Fruit crops are among the most sensitive plants to this problem.  In our experience the most susceptible types in order are: strawberries, blackberries, grapes, raspberries and apples.  Mild cases will result in poor growth, poor runner or new cane/branch production and poor quality and flavor fruit. Severe cases will result in plant death.

 As the soil ph increases the solubility of many nutrients is reduced. As a result these nutrients are precipitated as solid materials that plants cannot use.  For example the solubility of iron is 100ppm at a ph of 4, but drops to only.01ppm at a ph of 6.  At ph levels above 7.5, the amount of iron is often too low to sustain healthy plant growth.  While generally we have more iron in our soil than needed it may be in an unavailable form due to high ph.

 Plants differ in their ability to tolerate high ph soils.  In moderately alkaline soils, some plants can secrete high amounts of acids into the soil.  This lowers the ph immediately around the roots and increases nutrient availability. As the soils ph increases to 7.8 even these plants experience nutrient deficiencies. 

 There are many contributing factors that can bring on iron chlorosis and the interactions of these factors are not fully understood.  Plant competition, winter injury, soil compaction, excessive soil salt levels, excessive organic material, extreme soil temperature and light intensity and over watering can all lead to or aggravate a chlorotic situation. One common cause is the incorrect application of N-P-K chemical fertilizers

  How to Prevent Iron Chlorosis –

 Start with testing a good soil test. If you don’t know your starting point you won’t know how to get to where you need to be.  Check the soil ph and also the ph of the water you will be using to irrigate with. If you are in the 7 – 7.5 range you probably will not have any issues. If above 7.5 do the following. 

  • · Start your bed 1 year ahead of when you will plant it
  • · Use vegetative compost, no animal manures as these increase the soils salts levels and can aggravate the situation.  Try to achieve about 5% organic matter. Stable compost and the associated biological activity have a buffering affect on the ph.  
  • ·Flood the bed several times to leach accumulated salts below the root line.
  • ·If your soil does not have free lime add elemental sulfur.  A simple way to test is to take a teaspoon of the soil and dampen with vinegar.  If the soil fizzes you have too much lime for the sulfur to be effective. The bacterial action on the sulfur produces sulfuric acid which lowers the ph.  Sulfur will take around 6 months to start to become effective.
  • ·Add peat moss to your bed and mix in thoroughly.  Peat moss has a very low ph and will help bring it down in your soil.
  • ·Choose varieties that are known to be less sensitive.  In strawberries we have seen Sparkle a June bearer and Albion an ever bearer to be very susceptible to chlorosis.  Honeoye as June bearer and Seascape as an ever bearer are much less susceptible and better choices for New Mexico.

How to Deal with Iron Chlorosis if it Shows Up –

 The vast majority of the cases are brought on by over watering! It gets 90 degrees and our plants wilt (which is normal) but we assume they need more water.  We keep adding even more water as the situation gets worse and create a vicious cycle.  At the first sign of chlorosis decreasing the water will usually bring on a cure. The additional water also leaches away the acid environment the roots had developed immediately around them and now they cannot uptake iron. 

  • ·Add liquid elemental sulfur, this will work faster than the granulated as it will immediately get to the root zone where bacteria can use it.
  • ·Add a chelated iron.  This is a form of iron that will stay available longer than iron sulphate.  This may give some immediate results usually within 5-10 days.  If soil is above 7.5ph this may not be effective. Then you will have to use a form chelated with EDDHMA or EDDHA instead of the normal EDTA chelate.
  • ·If the situation is desperate use the iron chelate as a foliar spray.  This is the least recommended as it will take several applications and is a fine line between using enough to be effective and too much that will burn.  Chelated sprays are inactivated by sunlight so application is late in the day or at dusk.

 Again the benefits of a professional soil test cannot be overstated if you are serious about growing good fruits.  NMSU and many private labs offer this service for a reasonable charge.  If you want names or recommendations for labs, email or call us.