Yellow Vein Chlorosis

• The orange tree has tender roots that are easily harmed by diseases, drought and lack of nutrients. Injury caused by landscaping equipment also harms the roots. The ailing roots become unable to properly transport water and nutrients throughout the tree. The resulting lack of nutrients, especially nitrogen, causes the orange tree to develop yellow vein chlorosis. The leaves’ veins and surrounding tissue turn yellow, leaving the rest of the tissue green and healthy. This yellowing foliage appears sporadically throughout the orange tree.
  
  

Disease

• Several common citrus diseases cause the orange tree’s foliage to yellow and curl, including alternaria brown spot, greasy spot and leaf spot diseases. These fungal infections cause the orange tree’s leaves to develop blotches and spots of decay that are encased with yellow, dying tissue. While alternaria infections target the orange tree’s young foliage, greasy spot infections affect tree’s mature foliage. Leaf spot diseases infect foliage of all ages, although young foliage is most susceptible. Although unsightly, these diseases cause little harm when treated early. Fungicidal spray treatments are effective.
  
  

Rot

• Developing and germinating in the soil, phytophthora root rot infects the orange tree through its root system. It is a destructive disease causing progressive breakdown of the orange tree’s vascular system. The orange tree experiences an array of symptoms, including the shedding of roots and bark, girdling of infected tissue, yellow vein chlorosis, growth stunting, dieback, fruit drop and defoliation. The entire orange tree experiences a continuous breakdown until the tree is overwhelmed and killed by the infection. There are no cures for phytophthora rot infections. Remove and destroy the infected orange tree.
  
  

Waterlogged

• The orange tree requires a deep, well-draining planting location that receives at least eight to 10 hours of full sunlight each day. The soil should be loamy and nutrient rich with low salt content and pH levels between 6.0 and 8.0. Careful watering is essential. Avoid overwatering and waterlogged soils. The overwatered orange tree in a poorly drained environment quickly develops yellow leaves with necrotic margins and experience premature defoliation.
  
  

Nitrogen Deficiency

• The orange tree is a vigorous grower that demands ample amounts of nitrogen for healthy growth. As a result, the orange tree requires regular fertilizations throughout the growing season. The nitrogen-deficient orange tree displays its deficiency with light, yellowish-green foliage. The orange tree’s mature foliage experiences the loss of color first. The leaves become mottled and curled. Severe nitrogen deficiencies result in defoliation, stunted growth and the tree’s failure to fruit. The orange tree is also susceptible to magnesium, iron and zinc deficiencies, which result in similar symptoms. These deficiencies are easily prevented and treated with proper fertilization.