March 2011


Last weekend was good weather and a perfect chance to get trees pruned. Luckily at their small size not much pruning is required, mainly heading back central leaders to get more and better scaffold branching.  We also trimmed some scaffold branches back to get secondary branching on them.  It is amazing the different growth habits of different varieties.  Some are very stubborn with upright branches that need to come down more horizontal, some are reluctant to branch well. Some types had a profusion of good branches with no work on our part.  Having them in groups of 5 in one spot helps to see the differences in growth types. 

 This was also a good time to collect scion wood.  Scion wood is new growth from last year that is usually a terminal part of a branch. It is the name for the wood that is grafted onto rootstock.  Virtually all fruit trees varieties are grafted to a different type rootstock.  These rootstocks are types developed for different reasons.  Most are made to dwarf a tree’s ultimate size or are for disease resistance or possibly for different soil types.  We grafted about 25 apple trees on EMLA 7 rootstock this weekend.  EMLA 7 gives a tree about 60% of standard size, has good anchoring and is great for heavy or clay soils. 

The 2 basic graft styles we used were Whip and Tongue and Saddle graft. These 2 will work on most fruit trees although the commercial growers may use a different style. Both pieces of wood should match in diameter and be about pencil thickness. In this grafting the main points are to make even planes that will mate well with each other, to have the best contact with cambium wood (the layer just under the bark), to hold the pieces tight together and seal to prevent air getting into and drying the union. 

With the saddle graft the rootstock is cut at an angle on opposite sides so that it comes up to a point (an inverted “V”) and the scion wood is notched with a “V” shape cut at the same angle and length.  We found the hardest part was to get the cuts exactly 180 degrees opposite each other, also the “V” cut wants to just slide under the bark and give you a “U” shape cut.  Cutting the “V” takes practice and some skill.  It is best to wrap your fingers and thumbs with white medical tape first to prevent cutting yourself since you are cutting back towards you.  We used a box cutter razor knife and you will cut yourself if not protected!

    

The Whip and Tongue graft was much easier for us to accomplish.  You make 1 cut all the way through the rootstock at an angle with about a 1.5” cut, then halfway down make a cut in reverse to the start of the original cut.  Do the same on the scion wood and insert the pieces together.  If each cut is the same length and parallel it makes a very strong graft that holds together well.

 

 Always watch and make sure that your cuts will end up with the buds going upwards!  As soon as you have put the parts together you need to bind them tight with something that will give as the tree grows. We used grafting tape which is 5/8”wide clear polyethylene (non adhesive).  Just start wrapping in a spiral and tie off when you are past the graft.  Some people will use electrical or masking tape which will give or break when the tree grows.  Black tends to get too hot if the tree is grown in full sun before unwrapping.  After wrapping we then applied  Dr Farwell’s Seal and Heal  This is a paste that you brush on and it dries in 30 minutes to form a flexible long lasting, rot resistant coating impervious to water and air.

Many people just use the grafting paste or can get a good seal with just the tape.  Since we felt inexperienced we used both as a precaution.  We also kept the roots of the rootstock in a bucket of water except when we were actually working on them and the same for the cut ends of the scion wood.

Now all we have to do is wait for them to bud out and start growing, then we will see how good a job we did and how successful this was.  All in all not a bad way to spend part of a Saturday.

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.

.