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Desert Gardener: Iron chlorosis and other common citrus problems

November 10, 2001|By Keith Mayberry

Adviser, Imperial County-UC California Cooperative Extension

Chlorosis is a term used by botanists to describe the yellowing of normally green plant tissue because of a decreased amount of chlorophyll, often as a result of disease or nutrient deficiency.

While many homeowners are not familiar with the term, most have seen the effect on their plants. The pattern of yellowing on the leaves is somewhat characteristic for the cause of the problem. Plants often showing problems are citrus, eucalyptus, roses, stone fruits, apple, and many shrubby ornamentals.

Iron chlorosis is the most common problem seen. In a mild form, iron chlorosis is manifested as new leaves showing normal network of green veins but the areas between veins are yellow-green.

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In severe conditions, the leaves may loose all the yellow and become white. Green veins disappear. Leaf burn is prevalent and the leaves may fall off the plant.

The most common reason for the problem is that the soil has been too wet. In the late summer, the high demand for water prompts the homeowner to apply more water. For most plants this may not be a serious problem, but for some plants, a type of root shock sets in.

Plants need oxygen in order to efficiently take up iron. Therefore when there is no oxygen due to wet soils, less iron in the soil is available to plants. The same condition of saturated soils is likely to occur in the middle of the winter when the need for moisture is low and rain or a heavy irrigation oversaturates the soil.

The solution is not easy once the plants go into iron chlorosis shock. There are foliar sprays containing iron that can be used to green up leaves. This is a cosmetic fix.

Additional iron in the form of chelates, iron sulfate or other name brand products can help provide more iron, but you must correct the basic problem as well. That solution is to either carefully control irrigations or select different plants to grow in locations where flooding is prone to happen.

Lack of uptake of other nutrients can also cause chlorosis. Nitrogen deficiency appears on older leaves. The interveinal chlorosis caused by lack of manganese has a "Christmas tree" pattern, with the green not restricted to the veins as in iron deficiency. Zinc deficiencies look like iron deficiencies but the leaves are much smaller than normal. Most of these deficiencies (other than nitrogen) occur less frequently.

With citrus, fruit splitting often occurs at this time of the year. This is due to what we refer to as "start-stop" growth patterns. As the summer heat has hardened the skin and the growth of citrus fruits slows down. The skin sets firm and loses elasticity. Then when a few days of warm weather occurs along with irrigation, the fruit plumps up like a balloon. The rind won't give and a split occurs. Pomegranates often do this as well. This is a difficult problem to avoid and only careful irrigation can help.

This time of the year citrus fruit begin to change color. Unfortunately, color is not a good criterion to judge when to harvest. High-colored oranges and tangerines color well in California but generally not in Florida or the tropics. They even dye the fruit in order to make it more presentable for retail sales.

In general the longer citrus stays on the tree, the sweeter it becomes (up to a point). The best way is to taste test some samples and if you cringe, then wait.

Storing the fruit on the tree is much preferred over refrigerated storage unless there is a serious threat of a hard freeze coming.

Pick your fruit as you need it. Later in the season some Valencia oranges will get a green tinge again as the weather warms in early spring. Ignore the color change, as the fruit is still good.

Thick peel on grapefruit or other citrus is often the result of excess nitrogen fertilization. Next year back off on how much fertilizer you use and stop fertilizing in August.

Some limes and lemons are useable now. Oranges may have a ways to go. And normally, grapefruit is the last to mature. When harvesting be sure to clip the fruit from the tree rather than pulling it, which can leave a hole where fruit rots can begin.

Cut lemons down to a stub to prevent jabbing the other fruit in the bowl or box, as jab marks also cause decay to set in.

Normally tangerines are clipped with two leaves left on each fruit to make attractive displays in the home.

>> Questions? Send mail to: Desert Gardener in care of Cooperative Extension, 1050 E. Holton Road, Holtville, CA 92250

>> The Cooperative Extension serves all residents of Imperial County.

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