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Index : Plant Problems - Cultural
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- 10. Common Citrus Tree Problems - Top
- Citrus trees do reasonably well in the Tucson area. This, despite the fact that most types of citrus are native to regions of the world with a much milder climate than ours. Heat, drought, and intense sun combine to cause some problems we commonly see on citrus. Knowing what these problems are and how to treat them will result in healthier trees and more fruit.
At this time of year, probably the most common concern over citrus trees is the yellowing and dropping of older leaves. Fortunately, this is a normal leaf drop that all evergreen trees experience during the winter months. As leaves age, they drop off. On citrus, this usually occurs just prior to new spring growth. If you missed the recommended February fertilization, wait till May to apply fertilizer even if your tree looks anemic. Fertilizing too close to bloom can cause flowers to drop and new fruit to abort.
Unusually warm temperatures have prompted the early flowering of citrus trees. Often many of these flowers die. This is a natural occurrence by which the tree thins itself to carry only the fruit it can support. Some of the young fruit will also drop for the same reason. However, excessive heat and wind, common in the spring, can cause the excess flower and fruit drop. To counteract these conditions, make sure that soil is kept moist and a regular watering schedule is maintained. Let the irrigation run long enough to water the top two feet of soil. Use a soil probe or metal rod to push into the soil after watering. The probe will stop when dry soil is reached. Sometimes buried stones will be encountered. Push the soil probe in several locations to get an accurate reading. If the water hasn't penetrated the soil deep enough, water longer!
Sometimes, young leaves will be yellow. If the yellowing occurs in between the veins, while the veins remain green, it's likely an iron deficiency. This is an excellent time to apply iron to the soil around your citrus trees. With warming temperatures the iron is taken up by the trees and distributed to new growth and deficient mature leaves. Be sure to buy a chelated (water soluble) form of iron. It's more expensive, but it's the only type that works in our soil. Two excellent chelated types of iron are Sequestrene 130 and Sequestrene 330. Both work well on our alkaline, desert soils and one spring application lasts all season.
Curling of new leaves and whitish colored streaking in the leaves is a sign of thrip feeding. Thrips are tiny cylindrical flee-like insects that feed by scraping the surface of the leaf. As a result leaves become distorted, but remain green for the most part. Thrips feed on virtually all citrus trees. However, the damage they cause is insignificant and no control is necessary.
Another insect that causes concern, but little damage, is the orangedog catterpillar. The adult is the beautiful swallowtail butterfly. However, this larval stage is quite unattractive. It's brown and white coloration looks remarkably like bird droppings. Because it is a large catterpillar, about 2 inches long, it can consume many leaves. Simply pick them of by hand.
Fruit quality is most often effected by improper variety selection, picking the fruit before it's ripe, or not meeting the cultural needs of the tree. Sour grapefruit can usually be remedied by leaving the fruit on the tree longer. Grapefruit harvested in April will be much sweeter than those harvested back in January. Granulation, or drying of the juice sacs is another problem usually caused by insufficient watering. Thick peels occur mainly as a result of over fertilization or pruning. As a rule, citrus trees should not be pruned. Holes in fruit result from the pecking of birds. Bird netting will help discourage birds.
Finally, if a citrus tree lacks vigor, has poor fruit production and branch die-back, check near the base of the trunk. The first set of roots should be at, or near, the soil surface. If you must dig down around the trunk more than one or two inches to find the first set of roots, the tree has been planted too deeply, or soil has washed in around the trunk. In any event, this soil should be removed. A barrier should then be placed around the trunk to keep the soil from washing back. Soil in contact with the trunk will cause a slow decline and eventual death of the tree.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona 626-5161.
Material originally appeared in Arizona Daily Star gardening column, on March 21, 1999
- Updated: February 21, 2001
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