Plant Diseases


Commercial apples are sprayed anywhere from 10 to as many as 25 times in a growing season to bring that picture perfect fruit to market.  They are sprayed with toxic chemicals for prevention of early fungus, scab and viral disease, often sprayed with antibiotics to prevent fireblight and other bacterial infections, sprayed to promote thinning of the small apples, sprayed for control of coddling moth and other pests and on and on.  They are harvested green, put in cold storage and then given ethylene gas to promote artificial ripening. Many people will tell you just to wash them before you eat them or peel the skin off before eating (where most of the nutrients are) and you will get rid of any chemical residues.  I have a hard time believing that all these chemicals when combined and added up are really safe for us.

So what is an organic grower to do?  In many ways we are lucky to be inNew Mexico as most of the disease issues of fruits are related and cultivated in humid climates.  Our dry air and high UV is a natural inhibitor to many disease problems. Cedar apple rust and scab, 2 of the biggest problems are not found inNew Mexico.

The two largest pest issues (aside from birds and rodents) are the apple coddling moth and the apple maggot.   The apple maggot is just being found in a few counties in New Mexico and has not yet reached critical levels.  While you could use an “organic” pesticide such as rotenone, it is still a highly toxic poison. As with most pesticides they are non selective and will kill off beneficial insects as well as the “bad guys”

At this point we have adopted two solutions.  One is the use of a product named “Surround”

Made from modified kaolin clay, Surround® t is sprayed on as a liquid, which evaporates leaving a protective powdery film on the surfaces of

After spraying with Surround

leaves, stems and fruit. It controls a long list of insect pests on vegetables, fruit trees, ornamentals and more and is OMRI Listed for use in organic production. It is mixed about 2 cups per gallon of water and can be applied with a hand sprayer if you only want to do a few trees, or with a standard chemical sprayer for more.  Recommended application is 2 “coats” the second shortly after the first has dried.  It will need to be reapplied during the season as strong rains may wash it off.

Surround® works to protect plants and deter insects in three specific ways:

1.) Tiny particles of the kaolin clay attach to insects when they contact it, agitating and repelling them and possibly clogging their breathing pores.

2.) Even if the particles do NOT attach to their bodies, the insects find the coated plant/ fruit unsuitable for feeding and egg-laying. It just doesn’t look like a red apple any more! It is also thought that the light reflection from the white surface disorients the coddling moth especially.

3.) The protective white film cools plants by up to 15° Fahrenheit, which can help to reduce heat and water stress. Many fruits show improved color, smoothness and size with less russet, dropping, sunburn and cracking.  This in turn makes a stronger and healthier fruit and tree.

The second strategy is the use of apple maggot control bags.  These are a small bag that can be put over your apple and easily held on with a rubber band.  They are from a material similar to panty hose and stretch as the apple grows.  They allow sunlight, and water penetration and can be reused.  This is an effective barrier control method, preventing insects from laying eggs in the apples.  They also have an effect on birds which now ignore them.   Applying apple maggot control bags.

Both strategies should be started when your apples are about nickel size.

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We are all familiar with dormancy in deciduous trees during the winter but we don’t think of it happening in the summer. We are used to the norm: as the fall approaches and light diminishes and temperatures drop, the tree will go into a dormant period that lasts until the spring arrives. During the winter metabolism decreases and the leaves fall to the ground, but a low rate of metabolism is still maintained until spring. 

The key to dormancy seems to be the production of abscisic acid (ABA), a plant hormone. When ABA is first produced by the plant in fall, dormancy begins. This condition stays with the plant all winter, as does the hormone. With the coming of spring, the acid breaks up and the plant comes out of dormancy. 

However a plant can also go into dormancy to survive drought or an insect infestation. By shedding it’s leaves it reduces transpiration or water loss. Again the dormant stage is triggered by production of ABA, which can be produced as a reaction to plant stress, according to Kimball’s Biology Pages.  Many times the tree will stay dormant until the following spring and will regain health, provided the drought or disease outbreak does not continue. 

In some situations, such as breaking the drought by irrigating, you in effect can start spring all over again!  The tree in the picture is a 5 year old European pear which has had no supplemental water since June, 2010.     

We all know the drought we have been and still are in, very little snowfall and until a few weeks ago we only had about ½” precipitation since January 1, 2011.  The few little monsoon rains we have had this last few weeks tricked this tree into believing it was springtime again.  With this hormone break-up it sprouted leaves and even started blooming!  The key feature for us to note is that obviously this is a tremendous rootstock for pears in New Mexico, being well suited to living through the droughts, and will be the variety we would use most for grafting pears.

This year’s once in 40 or 50 years freeze was a good time to test the varieties we have chosen and I am glad to see they held up very well to what Mother Nature could throw at them.  If they made it through this winter they will make it in any other winter.   But I have had many questions based around  “Why is it that some trees get damaged and others of the same kind don’t at the same temperature?”  So here is my short list ( top ten list):

1. Variety type – The plant was originally developed to be a hardy variety maybe to be grown up north or from another country so is genetically predisposed to endure more.

2. Location – If they are the same variety but grown in different climates, generally the ones grown in a warmer locale will not handle the cold as well as the same variety in a  colder climate.  It just hasn’t “hardened” the same.

3. Wet Soil – will move cold fast whereas dry soil will hold more air and insulates the roots better, especially if it is a quick short freeze.

4. Organic soil content – see #4 above, more organics= more air in “looser” soil.

5.  Mulch –  versus none of course helps to insulate.

6. Wind – The same temperature with wind will affect trees greatly.

7. MicroClimate – large rocks or block walls will hold and release some heat helping protect plant.

8. Length of Time – While it got to a certain temperature, how long was it there?

9. Time of year – In the middle of winter when trees are fully dormant they can handle much more cold than in late fall or early spring, especially if there is some sap movement in these times.

10. General health – how the tree has been cared for, proper level of fertilization,  amount of water and growth in summer, hardening off for dormancy etc.

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.

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