Correcting Yellow Fruit Trees

Yellowing of the leaves of fruit trees (not citrus) can be caused by a lack of available iron, insects, diseases including viruses, and watering. We will focus on yellowing due to a lack of available iron. if you were looking for citrus, click below.

Yellowing Citrus 

 

Yellowing and Alkalinity

Soil pH is a fancy way to talk about soil alkalinity. pH is a logarithmic scale just like the earthquake scale. The earthquake scale is from 0 to 10. The pH scale is from 0 to 14. pH is how alkalinity is measured. This pH scale runs from 0 to 14 with 7 being neutral…a pH of 7 is where there is a balance, an equal amount, between too much and not enough alkalinity.

This pH scale is available from http://www.ns.ec.gc.ca/

Available vs Nonavailable Iron

 

Notice the correct term is AVAILABLE iron. This is because iron is sometimes NOT available in soils but it is there. It is because of soil pH or its level of alkalinity measured by soil pH. It is not in a form available to plants. The form of iron available to plants is when the pH is 7. When soil pH is above 7, iron is less available. Remember that pH is measured LOGARITHMICALLY, like an earthquake scale. So when iron is in the soil and the soil pH goes from 7 to 8, the amount of iron is LESS by ten fold! From 7 to 9 it is less available by 100 fold!

A pH chart showing availability of some plant nutrients as the pH changes from 4.0 to 10.0. How wide the bar is says how available that nutrient is. The pH of our soils are just below to slightly above 8.0. Notice that the minor elements of iron, zinc and manganese are limited at this pH. http://ipm.uconn.edu/documents/raw2/html/546.php?display=print

 

Iron is best available to plants when the soil pH is 7, called neutral. Our desert soils range from a pH of about 7.8 to 8.2 in most cases. So iron availability to plants is sometimes a problem. This problem many times happens in spots in soil. Iron availability is never consistent in soil. Iron is nearly always there but the pH is not consistent from place to place.

 

Two Methods of Making Iron Available

There are two ways of making iron available to plants; change the soil pH in these spots to closer to a pH of 7 and make the soil pH lower OR give the plant iron in a form that wont change its form with more alkalinity. There are many problems with using chemicals to lower the alkalinity of the soil (it doesn’t last long, the soil must be warm and wet and in a form that will work in the soil rapidly.) Chemicals that lower the alkalinity (soil pH) include different types of pure sulfur (but not sulfates), acids, and soil chemical amendments like aluminum. Some spots of soil are more difficult to lower the alkalinity than others.

Sulfur and Lowering Soil pH

Sulfur and Lowering Soil pH 2

Sulfur and Lowering Soil pH 3

EDDHA chelated iron makes iron available to plants regardless of the alkalinity (soil pH). But iron must be attached to this chelate or it will not work because there would be no iron, just EDDHA. So the chemical that works is correctly called “ iron EDDHA”. Usually manufacturers of EDDHA can get about 6% iron to attach to it.

I dont understand why only Viragrow carries this type of chelated iron. Maybe because it is more expensive than Kerex and other types of iron. It is the only form of iron that will work in soils of all pH ranges. Otherwise take your chances and hope your soil is below 7.6 in pH if you are using another type of iron.

Primer on Chelated Iron Chemistry

When using chelated iron in the form of EDDHA (acronym for ethylenediamine-N,N′-bisdihydroxyphenylacetic acid and why we call it EDDHA). EDDHA iron is a chelated form of iron. When it holds iron in its claw-like grip the iron is in a stable form. This iron EDDHA is stable from a pH of 0 to 14. There are other iron chelates less expensive than iron EDDHA but will not hold the iron when the pH changes. This is not true when iron is gripped by other chelates like EDTA and DTPA. Both of these chelates will no longer hold iron when the soil pH is about 7.5 to 7.6. If the soil pH is more than this, they don’t work! Using these iron chelates can be a crap shoot. As soon as these chelates release their iron it changes to a form not available to plants but the iron is still there! EDDHA will not release the iron regardless of the pH or alkalinity. It holds iron tight all through a range of alkalinity from 0 to 14. But when iron EDDHA finds a plant, it releases the iron from its grip and the iron is released to the plant before most of it changes to another form!

This is called a "chelate stability diagram" regarding the pH. If you are comfortable reading this diagram it shows you how EDDHA chelate is stable in soils from a pH of 4 to 10 (bottom line). https://cropnuts.helpscoutdocs.com/article/826-iron-fertilisation

Timing of Application

Because iron, once inside plants, does not move, iron EDDHA must be applied to the soil when plants are growing and producing new leaves and stems. This means after the plant stops growing (mid to late summer) the soil application will not work. In fact, it stops working sometime around April or May. This means iron EDDHA must be applied to the soil between February 1 and about early April for best results. The more that the plants has grown and produced its leaves, the less iron EDDHA will work. 

So the ideal time for iron EDDHA to be applied to the soil is just before growth starts in the spring, around February 1. I would recommend putting iron EDDHA in the EZ flow fertilizer injectors along with the first application of fertilizer in the spring.

 

Fruit Trees Most and Least Susceptible to Yellowing from Iron

The fruit trees most susceptible to yellowing due to iron availability include peach, nectarine, plum, apple, pear and cherry. Mostly the stone fruit. Moderately susceptible include quince and persimmon. Less susceptible include pomegranate, jujube, and fig.

 

Yellowing Later in the Season

Sometimes yellowing of leaves and new growth occur later in the growing season when available iron is not moving inside the plant but new growth is slowing down. After sometime about April or May, soil applications of EDDHA iron no longer work. At this time foliar feeding of iron is recommended to try. Mix iron EDDHA in a spray tank along with a surfactant, keep it agitated, and spray the leaves with this iron solution until the leaves begin dripping from this application. The pH of the water is not a problem for EDDHA. But for other types of iron sprays it probably is. Adjust these spray solutions for iron to a pH of 6.0 to 7.0.

 

What if Nothing Works?

Sometimes yellowing is not because of a lack of available iron. Foliar sprays with test bottles of manganese may be the problem because shortages of manganese can look very similar to iron deficiency. Zinc deficiency has other visible signs that point in its direction.