Yellow leaves on a peach tree, a condition called chlorosis, indicate the tree is struggling to produce chlorophyll. Chlorophyll is the green pigment necessary for photosynthesis. Its absence suggests an underlying issue restricting nutrient uptake or damaging the leaf structure. Identifying the specific pattern of yellowing and accompanying signs is the first step toward diagnosis. This guide covers common causes, including environmental factors, pests, and diseases.
Environmental Stressors and Soil Issues
The most frequent cause of chlorosis relates to the tree’s root system, specifically moisture levels and soil chemistry. Both extremes of water availability cause leaves to turn yellow and drop prematurely. Underwatering leads to drought stress, causing leaves to dry out and display brown edges before yellowing. Conversely, prolonged overwatering can lead to root rot, starving the tree of oxygen and nutrients.
A high soil pH (alkaline conditions above 7.0) often causes yellowing by locking up essential micronutrients. Iron (Fe) and Manganese (Mn) become insoluble in alkaline soil, even if present. This results in interveinal chlorosis, where the tissue between the leaf veins yellows while the veins remain green. Uniform yellowing across the entire leaf, starting on older foliage, usually points to a deficiency of a mobile nutrient like Nitrogen (N).
Root rot diseases are fungal infections caused by poor drainage and saturated soil. These infections damage the root system’s ability to absorb water and nutrients. When roots are compromised by pathogens such as Phytophthora species, above-ground symptoms mimic severe nutrient deficiencies or drought. Improving soil drainage and preventing soggy conditions is necessary to prevent this stress.
Insect Pests Causing Chlorosis
Insect pests feed on peach leaves, directly resulting in the loss of chlorophyll and yellowing. Mites, specifically spider mites, are minute pests that pierce leaf cells and suck out the contents. This feeding leaves behind tiny yellow or white dots known as stippling. Severe mite infestations cause the leaves to take on a bronzed or dusty yellow appearance, often visible on the underside of the foliage.
Sap-sucking insects, such as aphids and scale, congregate on new growth and stems, draining the tree’s vascular system. This continuous feeding weakens the tree, leading to general yellowing and curling of the leaves, which may be coated in honeydew. Root-knot nematodes reside in the soil and damage roots, creating galls that prevent the uptake of water and nutrients. The resulting canopy yellowing is a secondary symptom of this root disruption.
Common Fungal and Bacterial Infections
Several pathogens cause chlorosis, often accompanied by unique leaf deformities. Peach Leaf Curl, caused by the fungus Taphrina deformans, is a common spring disease characterized by puckered, thickened leaves that initially display red or purple blisters. These distorted leaves eventually turn yellow and drop, forcing the plant to expend energy on a second flush of foliage.
Bacterial Spot, caused by the bacterium Xanthomonas arboricola pv. pruni, begins as small, dark, water-soaked spots on the leaves. As the spots mature, they become angular and necrotic, surrounded by yellow tissue. This eventually leads to premature defoliation. The disease is problematic in areas with high humidity and is often spread by wind and rain.
Crown and root rots, like those caused by Armillaria fungi, attack the lower trunk and roots of the peach tree. These infections girdle the tree’s vascular tissue, blocking the flow of water and nutrients to the canopy. The foliage responds by developing a generalized, often reddish-tinged chlorosis and wilting, indicating the transport system is failing.
How to Diagnose and Treat the Problem
Accurate diagnosis begins by examining the pattern of yellowing across the tree’s canopy. Note if the chlorosis is generalized across the entire leaf and tree, which points toward water stress or a mobile nutrient deficiency like Nitrogen. Interveinal yellowing, where the veins remain green, indicates an Iron or Manganese micronutrient deficiency, often caused by high soil pH.
Check the soil conditions by testing the moisture level several inches below the surface and obtaining a professional soil pH test. Peach trees thrive in slightly acidic soil, ideally between pH 6.0 and 6.5. A high pH reading confirms a nutrient lock-up issue. If the soil is alkaline, a temporary solution for iron chlorosis involves applying chelated iron products directly to the soil or as a foliar spray for quicker uptake.
A physical inspection of the leaves’ undersides and new shoots helps identify pest presence, such as the webbing associated with spider mites or the sticky residue from aphids. If a fungal disease like Peach Leaf Curl is suspected, look for thickened, blistered leaves. Treatment for this is preventative, requiring a dormant-season application of a copper fungicide in late fall or early spring before bud swell. Adjusting the watering schedule and ensuring excellent soil drainage are effective long-term corrective actions for many problems.