Centipede grass is a warm-season turf common across the Southern United States, favored for its low-maintenance requirements. When the grass turns yellow, the condition is called chlorosis. This discoloration is a concern because centipede grass is sensitive to its environment and nutritional intake. Yellowing is a symptom indicating an underlying issue, usually related to soil chemistry or cultural care practices.
Nutritional Imbalances
The most frequent cause of yellowing in centipede grass is the soil’s chemistry, specifically its pH level. This turfgrass thrives in highly acidic soil, ideally between 5.0 and 6.0 pH. When the soil pH rises above this range toward neutral or alkaline conditions, the grass develops iron chlorosis.
Elevated pH chemically locks iron into a form the shallow roots cannot absorb, even if the iron is present in the soil. Since iron is necessary for chlorophyll production, the grass struggles to stay green. This deficiency causes interveinal chlorosis: the newest leaves turn pale yellow while the veins remain a darker green.
A soil test should confirm the pH and iron content. If the pH is high, applying a soil acidifier like elemental sulfur can slowly lower the pH, making the iron available. For a faster, temporary fix, a foliar application of chelated iron supplement can be sprayed directly onto the leaves for quick green-up.
A secondary nutritional issue is general nitrogen deficiency, which presents differently than iron chlorosis. Nitrogen-deficient grass displays a uniform, pale yellow color affecting the older growth first. Centipede grass requires minimal nitrogen, and over-fertilization can be as damaging as deficiency.
Environmental Stress and Water Management
Yellowing can result from environmental factors, particularly water availability and temperature extremes. During drought, grass blades curl inward and turn gray-green before progressing to yellow or brown. Centipede grass has shallow roots, making it highly susceptible to drying out during low rainfall.
Drought stress requires a deep and infrequent watering schedule, providing about one inch of water per week. Overwatering causes saturated soil, leading to shallow root development and root rot. Root rot inhibits nutrient uptake, resulting in yellow decline. Watering deeply but allowing the soil surface to dry encourages a healthier root system.
Temperature also causes discoloration, especially in cooler months. Centipede grass enters winter dormancy when soil temperatures drop below 55°F. During dormancy, the grass uniformly turns a straw-yellow or brown color, which is a normal survival mechanism. Extreme heat in summer can also cause temporary yellowing; raising the mowing height slightly can help mitigate this stress.
Identifying Pests and Disease Damage
Yellowing that appears in distinct patches or patterns is likely caused by pests or fungal disease. Several subterranean pests feed on the roots, hindering the grass’s ability to absorb water and nutrients, resulting in a yellow appearance. Nematodes, microscopic roundworms, damage the roots and cause general decline and stunting across the turf.
White grubs, the larvae of various beetles, chew through the roots. This often causes localized yellow or brown patches that can be easily rolled back because the root system is destroyed. The ground pearl, a type of scale insect, attaches to the roots and sucks out the plant’s juices, causing yellow patches that may resemble a fungal infection.
Fungal diseases manifest as irregular or circular yellow and brown spots across the lawn. Large Patch is a common fungal infection affecting centipede grass, particularly during cool, wet weather in spring or fall. While fungicide application helps manage the issue, reducing excessive irrigation and nitrogen fertilization is the most effective preventive measure.
Correcting Mowing and Chemical Application Mistakes
Cultural practices, such as mowing and chemical treatment, can induce yellowing through direct stress or injury. Scalping the lawn—mowing too short—removes too much photosynthetic leaf tissue. This forces the grass to use stored energy to recover, resulting in temporary yellow-brown discoloration.
To avoid scalping, centipede grass should be maintained at a height of 1 to 2 inches. The “one-third rule” should be followed, meaning no more than one-third of the grass blade height should be removed in a single mowing.
Chemical Application Mistakes
Improper chemical application is a frequent source of yellowing or browning, often called chemical burn. Fertilizer burn occurs when too much nitrogen fertilizer is applied, or when applied unevenly. This causes a high salt concentration that draws water out of the grass cells, resulting in rapid, localized yellowing or browning.
Centipede grass is highly sensitive to certain herbicides, such as 2,4-D. These chemicals can cause significant yellowing or decline if applied incorrectly or during high temperatures. Always read product labels carefully and avoid applying chemicals during the peak heat of the day to minimize the risk of stress and burn damage.