- Author: Ed Perry
For many in California, the backyard orange or grapefruit tree is almost a member of the family, and any negative change in its appearance elicits concern. One such change in appearance is leaf yellowing and drop that often occurs during the winter in citrus. Citrus leaves can remain on the tree for as long as three years depending on tree vigor, but disease, inadequate or excessive nitrogen fertility, excessive salt or born in the soil, poor irrigation practices, freezing temperatures, pest pressures and low light levels significantly reduce leaf longevity. Excessive leaf drop during the growing season is more likely to indicate a serious problem than leaf drop during the winter. Winter leaf drop normally reflects nothing more than a momentary swing in the natural balance between the natural elimination of old senescing leaves and their replacement.
Reduce winter water applications to citrus trees that have defoliated or that have a significantly thinning canopy. Trees like this require little, if any, supplemental irrigation. Even a mature tree with a full leaf canopy will require less than 10% of the water that it would require during the summer.
The best indicator of tree health for a defoliating citrus tree during the winter will be how well it produces the first flush of new growth in the spring. A decision to keep or remove a citrus tree based on tree health should not be made during the winter. Even trees that lose most of their leaves during winter are capable of replacing leaf canopies with the spring flush of growth, usually with little loss in fruit production. Trees that do not produce a vigorous flush in early spring may have a more serious problem. March is an excellent month to begin applying fertilizer to encourage new leaf growth and fruit production and to help keep an old friend of the farm or family backyard around for years to come.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
- Author: Ed Perry
Splitting of navel oranges is a disorder that shows up every few years in the Northern San Joaquin Valley. It's difficult to predict the problem, and once you see oranges beginning to split, it's too late to do anything about it. However, it may be useful to talk about why splitting may occur, and what you can do to help lessen the problem.
While you may not notice it until the fruit begins to ripen, splitting in navel oranges begins in green fruit. The split usually starts at the stylar or navel end of the fruit, the weakest point in the rind. The split may be short and shallow, or it may be deep and wide, exposing the segments. Splitting is most serious in navel oranges, but it may occur in Valencia oranges too.
It is not well understood just what causes splitting, but it's thought to be caused mainly by a combination of environmental conditions. Some studies show that changes in climate such as temperature and relative humidity may have more effect on splitting than anything else. A couple of my citrus reference books indicate that splitting is caused by hot, dry weather, alternating with humid, cloudy weather. Allowing the soil to dry out too much between irrigations is believed to result in increased splitting. However, other research and observations in orange groves have shown that irrigation, fertilizers and other cultural practices make no difference in the amount of splitting that occurs in any given year.
It is obvious that you cannot control all of the factors that cause splitting, since weather conditions are involved. However, you may be able to minimize the problem by making sure that your orange tree is well watered. Remember that orange trees (as well as other citrus) are not drought tolerant and need a constant supply of moisture in the root zone. If your soil is sandy you may need to water a fully-grown orange tree every ten to fourteen days during the summertime. In clay soils, the watering schedule may be every fourteen to twenty-one days. You should continue to water your trees periodically in fall, at least until rain begins.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
