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Index : Citrus and Other Fruits
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- 8. Citrus Tree Die-back - Top
- The recent cold has frozen the outer growth of many citrus trees here in Tucson. In most cases only the leaves were killed, but some stems might also have frozen. But this damage is temporary and will not effect the overall health of the trees. However, a general die-back of citrus stems and branches is a serious problem and indicates a problem with either the trunk of the tree or the root system.
Damage to the trunk of a citrus tree can occur when soil comes in contact with the base of the trunk. This can happen if the tree was planted too deep, or settled in the planting hole. Citrus are very sensitive to having any soil against their trunks. Even an inch of soil covering the trunk is enough to damage the sapwood and result in a stunting and eventual die-back of the branches. If this soil is not removed, over time, the tree will likely die.
Citrus that are watered by basin irrigation are also likely to have soil that has accumulated around the trunk. It’s a good idea to check the trunk two or three times during the year and to pull back any build-up of soil. You should be able to see where the first set of roots come out from the base of the trunk.
Both over-watering and under-watering are also causes of die-back in citrus. Over-watering keeps the soil too wet, blocking soil pores and preventing oxygen from passing into the soil and down to the roots. Without adequate oxygen, and in the presence of water, fungus present in the soil can attack and kill roots. This condition is known as root rot. As the roots die, a corresponding death of the branches occurs, starting with the outermost stems and moving inward.
Under-watering can also cause die-back. When the tree is not getting enough water, those stems and branches farthest from the roots are the first to die. A rolling of the leaves, similar to the rolling of a cigar, is the first sign of inadequate watering.
To avoid problems of over or under-watering follow proper citrus watering practices. Established trees, those planted longer than one year, should be watered once a week during the warm months (April - October) and once every two weeks during the cool months (November- March). But critical to this schedule is deep watering. The tree should be watered long enough or with enough water to soak the soil to a depth of 3 feet. To do this, use a metal rod, such as a five foot long piece of re-bar which can be purchased at hardware or building supply stores. The rod can be pushed down into moist soil, but will stop when dry soil is hit. Because of the likelihood of hitting buried rocks, push the probe down in several locations to get an accurate reading.
Over time salts building up in the soil can also cause citrus stems and branches to die. Salts naturally occur in desert soils, but salts are also added by fertilizing and through irrigation. The amount of salt in irrigation water is small, but without an occasional flushing, these salts can accumulate to harmful levels.
To prevent or to correct a salt buildup, citrus trees should be watered heavily at least twice yearly. A heavier watering than normal will help dissolve excess salts and flush them down below the roots. The best way to accomplish this is to coil a soaker hose under the tree and let the water slowly seep out for 10 to 12 hours. The best times of year to do this heavy watering is during a rainy period in the Winter and again during the Summer Monsoon season.
Finally, citrus trees do have a normal life expectancy. Under good conditions and in milder climates, citrus trees may live to 50 years or more. But here in the desert that life expectancy is considerably shorter. A 30 year old citrus tree is considered old and at about that age, it will begin to gradually decline with a dying back of stems and branches. At that point, it’s best to plant a new, vigorous citrus tree to replace it.
“Buying the Best Garden & Landscape Plants” will be the topic for this week’s garden demonstrations. They will be presented on Wednesday at 9 a.m. at the Pima County Extension Center, 4210 N. Campbell Ave (central); and at 1 p.m. at the Wilmot Library (east), and on Friday at 1 p.m. at the Oro Valley Public Library (northwest).
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: February 1, 2004
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