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Tuesday, June 2, 2015

Sap from Grapefruit Possibly Gummosis Disease

Q. I am having a problem with my grapefruit tree. The branches have some sap coming from them and the leaves are yellow.
Sap coming from the branches of grapefruit tree could be Rio Grande Gummosis Disease which developed from winter freezing injury.

A. The yellowing of the leaves usually indicates the soil is being kept too wet or a need for a specialty fertilizer such as iron.
This is what the tree looks like with gumming on some branches. Notice that one of the branches has a lot of yellow leaves. Damage to branches can also lead to micronutrient deficiencies.
I saw the sap coming from a stem in the picture you sent. This could be from a disease common to grapefruit that have suffered freeze damage during the winter. It is called Rio Grande Gummosis disease which can occur to grapefruit trees suffering from a past stress. A common stress is winter or freezing damage.

Gum forms on the trunk or branches and causes blisters on the trunk. If you cut into the branch or trunk you can see pockets of gum under the bark. If you make a long cut into the wood through the blistered area and into fresh wood you may see a pinkish discoloration in the fresh wood.
Most likely the tree will continue to decline if this is the case. I would remove the tree and find a warmer spot to grow citrus that does not have much winter wind. Wind makes winter freezing temperatures worse.

I would also make sure the soil drains freely when water is applied and use wood chips as a surface mulch to help keep the soil healthy.

You can read more about this disease on grapefruit here from the University of Arizona and copied below.

Rio Grande Gummosis
This name has been given to a gumming disease of mature citrus, particularly grapefruit, thought to be caused by several fungi, but no particular pathogen has been identified.

Symptoms: Symptoms begin as narrow cracks in the bark of limbs and trunk in which a yellow, water soluble exudate accumulates. Gum formation on the trunk or branches and gum exudation from blisters on the trunk continues and forms gum pockets under the bark. The advancing margin of infection is orange to pink. Once sapwood is exposed, wood decay may begin. In later stages of disease, heart rot may also be prevalent.

Control: Several factors have been identified as contributing to disease including freeze damage, poor drainage, and salt accumulation. Weakened and injured trees seem to be predisposed the disease. There is no control other than cultural practices that keep trees in vigorous condition. Good pruning practices that remove freeze damaged wood and encourage fast healing are the best way to prevent disease.

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