Chlorosis

• Chlorosis of peach trees appears as a yellowing of the leaves of the tree between their veins, which remain green. A nutrient deficiency is the culprit in this particular situation; a lack of iron or soil that is too alkaline causes chlorosis. Add a fertilizer to soil that has a high iron content and perform a soil test to determine the pH of the soil; if the soil is above 7, it is in the alkaline range.
  
  

Water

• Drought is another cause of yellowing leaves on a peach tree. Dry soil that lacks water dehydrates the peach tree, which will re-enter a dormant state until sufficient water is present. A lack of water causes the leaves to turn yellow or brown, starting at the tips. Peach trees grow best in soil that remains slightly moist throughout the growing season. Water the tree weekly during dry spells to keep the leaves healthy and green.
  
  

Pest Problems

• Serious pest infestations from insects such as aphids can cause the leaves of a peach tree to turn yellow; the insects damage the leaves. Pest insects such as spider mites and scale insects feed on the leaves of peach trees, sapping them of nutrients and leaving them susceptible to diseases. As the leaves weaken, they will turn yellow. Yellowing often begins at the edges of the leaves, where they are damaged. Apply pesticides to the peach trees to keep the leaves protected.
  
  

Leaf Spot Diseases

• Some fungal leaf spot diseases cause the leaves of a peach tree to turn yellow over time. The presence of yellow or brown spots on the leaves is a primary indicator of leaf spot diseases, and as the fungus spreads, it will cover the leaf or kill it, causing it to turn yellow before it falls from the tree. Spray the peach tree with a fungicide to kill the spores of the leaf spot disease.