Orange Tree Culture & Diseases

It’s easy to give your family the vitamins they need when you serve delicious fresh fruits such as oranges. When you grow your own orange tree, it’s even easier, because you’ll have a plentiful supply of seasonal fruit that you can make into juice, marmalade, chicken with orange sauce and many other dishes. Orange trees are also easy to care for, but they can develop several plant diseases you should watch for and treat early.

Cultural and Environmental Needs

The most important cultural needs of orange trees are sunlight, well-drained soil and temperatures that rarely drop below freezing (32 degrees F). If you build a raised bed or grow your orange tree in a large container using a porous, rich, fast-draining potting soil, your tree’s roots will be able to dry out slightly between waterings and will not develop root rot, which can kill your tree. If your winters are typically cooler, with extended periods of below-freezing temperatures, it’s wise to grow your orange tree in a large pot and move it indoors before your first fall frost.

Water and Fertilizer

Orange trees need water once every week or 10 days during their active growing season, from early spring until fall. Allow the soil to dry out before adding more water; you can check it with your finger by inserting it about 2 inches deep. If the soil is dry at that depth, flood your tree with at least 5 gallons of water. Orange and other citrus trees will produce the largest fruit and the largest quantities of fruit if you fertilize them on a regular basis. Special plant foods are available for citrus trees; use such a product three to four times during your tree’s active growing season according to label instructions.

Yellow Vein Chlorosis

If the veins and midribs of your orange tree’s leaves turn yellow, leaving the rest of the leaf green, it might be suffering from an iron deficiency. If it spreads, all of the leaves on the tree can become yellow. This unsightly situation is easy to remedy by feeding your tree with chelated iron or another type of iron supplement. Mix it according to product label instructions and apply it around the tree’s drip line, which is usually about 2 to 3 feet from the trunk on medium-sized trees. When the tree begins to send out new growth, it will not have the yellow coloration. Old leaves might fall; this is a normal occurrence.

Powdery Mildew

This fungal disease is common on citrus trees. You’ll know if your tree has contracted it if you see white to gray fuzz on the leaves. It’s wise to begin treating your infected tree as soon as possible after the mildew sets in by spraying your tree with a sulfur-based spray. Powdery mildew is made worse when aphids and scale insects are present; their excretion is a sticky substance called honeydew, which can create a favorable growing ground for the mildew spores. Ants often carry these insects to a plant and feed off the honeydew, so protect your tree from ants by using a pest barrier product such as Tree Tanglefoot around the lower portion of the trunk. If aphids or scale are numerous, spray your tree with insecticidal soap several times until all insects appear to have died.

Greasy Spot Fungus

This fungal disease causes yellow or brown blisters to form on the undersides of your orange tree’s leaves. The remedy for this disease is liquid copper fungicide, which is considered to be an organic product. Follow label instructions for safe and proper mixing and application of such a product; even though it is organic, it can possibly cause detrimental health and environmental effects if you use it incorrectly.

Keywords: orange tree care, citrus diseases, mildew greasy spot

About this Author

Barbara Fahs lives on Hawaii island, where she has created Hi'iaka's Healing Herb Garden. Fahs wrote "Super Simple Guide to Creating Hawaiian Gardens," and has been a professional writer since 1984. She contributes to Big Island Weekly, Ke Ola magazine, GardenGuides and eHow. She earned her B.A. at UCSB and her M.A. from San Jose State University.