Bermuda grass, a warm-season turf, is known for its resilience, but even this robust grass can turn yellow, signaling underlying issues. Understanding the reasons behind this discoloration is key to restoring your lawn’s health and vibrant appearance.
Environmental Factors
Watering Issues
Both insufficient and excessive watering can cause Bermuda grass to turn yellow. Under-watered grass appears dull, turning bluish-gray before yellowing and browning. It feels dry and brittle, and footprints may remain visible, indicating a lack of water. The soil beneath will likely be hard and dry.
Conversely, overwatering also leads to yellowing, often with a spongy feel. Excess moisture suffocates roots, causing them to rot and hindering nutrient absorption. This can also promote moss, algae, or fungi. Bermuda grass needs about 1 to 1.5 inches of water weekly from rainfall or irrigation. Water deeply and infrequently, encouraging roots to grow 4 to 6 inches deep. Watering early morning (4 AM to 10 AM) improves absorption and reduces fungal disease risk.
Temperature Stress and Dormancy
Extreme temperatures, both cold and excessive heat, can induce yellowing in Bermuda grass. During colder months, below 50-55°F, Bermuda grass naturally enters dormancy. This causes the grass to cease active growth and turn straw-like yellow or tan as a protective measure. While dormant, the grass is not dead; it conserves energy and greens up when warmer temperatures return.
Prolonged intense heat and drought also lead to stress-induced yellowing, even if not fully dormant. This happens when the grass struggles to absorb enough water to cool itself and maintain functions. This yellowing is a symptom of dehydration and stress. Adequate, deep watering during hot, dry spells mitigates this stress and prevents severe discoloration.
Nutrient and Soil Problems
Nutrient Deficiencies
A lack of essential nutrients can cause Bermuda grass to yellow. Nitrogen is crucial for chlorophyll production, which gives grass its green color. A nitrogen deficiency typically causes an overall pale green or yellowish hue across the lawn, with older leaves showing symptoms first and potentially turning straw-like. This indicates insufficient nitrogen for vigorous growth and vibrant color.
Iron deficiency, or iron chlorosis, appears differently. While nitrogen deficiency causes uniform yellowing, iron deficiency often shows as interveinal chlorosis: areas between leaf veins turn pale yellow or white, while veins remain greener. This symptom shows on younger grass blades first. Iron is essential for chlorophyll synthesis, and its unavailability leads to this distinctive striped appearance. A professional soil test is recommended to diagnose deficiencies, ideally between March 15th and April 30th for warm-season grasses. This test provides nutrient levels and guides fertilization strategies, such as applying nitrogen-rich fertilizers or iron supplements.
Soil pH Imbalance
Soil pH significantly impacts nutrient availability for Bermuda grass. Bermuda grass thrives in a slightly acidic to neutral pH range, between 5.8 and 7.0. When soil pH falls outside this optimal range, grass roots may be unable to absorb essential nutrients efficiently, even if present.
An imbalanced pH can lock up nutrients, making them inaccessible and leading to symptoms mimicking deficiencies, including yellowing. For instance, in highly alkaline soils, iron becomes less available. Soil pH testing identifies this issue, and adjustments can be made by adding amendments like lime to raise pH or sulfur to lower it, improving nutrient uptake and grass health.
Soil Compaction
Soil compaction occurs when soil particles are pressed together, reducing pore space. This restricts air, water, and nutrient movement to grass roots. When roots lack adequate oxygen, water, and nutrients, Bermuda grass becomes stressed, leading to stunted growth and yellowing. Compacted soil also impedes healthy root development, forcing shallow roots, making the grass vulnerable to environmental stresses like drought and heat. Aeration is an effective solution to alleviate compaction, improving air and water penetration, allowing roots to grow deeper and access necessary resources for a healthy lawn.
Pests and Diseases
Insect Pests
Insect pests can cause Bermuda grass to yellow by feeding on roots, stems, or blades, disrupting water and nutrient absorption. White grubs, beetle larvae, are common culprits. These C-shaped grubs feed on grass roots, leading to irregular yellow or brown patches that feel spongy. Infested turf can often be rolled back due to severed roots.
Chinch bugs are tiny insects that pierce grass stems, sucking fluids and injecting toxins, causing grass to yellow then brown in irregular patches. They are active from late spring through fall. Sod webworms, the caterpillar stage of lawn moths, feed on grass blades at night, causing chewed appearances and yellow to brown patches. Identifying the specific pest is key for effective treatment with appropriate insecticides.
Fungal Diseases
Bermuda grass is susceptible to several fungal diseases that cause yellowing. Dollar spot appears as small, circular, straw-colored patches that can merge into larger areas. This disease is associated with prolonged leaf wetness and nitrogen deficiency. Brown patch, another common fungal disease, causes circular or irregular patches of thinned, brownish-yellow grass. It is favored by high humidity, warm temperatures, and excessive nitrogen fertilization.
Rust disease manifests as powdery, orange-yellow pustules on grass blades that rub off easily. This infection weakens the grass, leading to widespread yellowing. Fungal diseases thrive in conditions of excessive moisture, poor air circulation, or nutrient imbalances. Proper cultural practices, such as deep, infrequent watering, improved drainage, adequate air circulation, and balanced fertilization, help prevent outbreaks. In severe cases, specific fungicides may be necessary to control the disease and allow recovery.
Maintenance Mistakes
Improper Mowing
Incorrect mowing practices stress Bermuda grass and lead to yellowing. Mowing too short, or scalping, removes too much green leaf blade, exposing yellow or brown stems. Bermuda grass stores energy in its green blades; excessive removal depletes these reserves, hindering photosynthesis and causing widespread discoloration. While Bermuda grass tolerates lower mowing heights, a height of 1 to 2 inches is recommended for common varieties.
Using a dull mower blade is another issue. A dull blade tears and bruises grass blades instead of cleanly cutting them, leaving ragged tips that quickly turn yellow or brown. This damage makes the grass more susceptible to disease and environmental stress. Sharpening mower blades ensures a clean cut, promoting healthier regrowth and a uniformly green appearance. Adhere to the “one-third rule,” removing no more than one-third of the grass blade in a single session.
Chemical Application
Improper application of lawn chemicals, including herbicides, pesticides, and fertilizers, can stress Bermuda grass and cause yellowing. Too much fertilizer, especially high-nitrogen types, can lead to chemical burn, turning grass blades yellow or brown due to excessive salt. This also occurs if fertilizers are applied unevenly or not adequately watered after application, preventing proper nutrient dissolution.
Similarly, incorrectly applied herbicides or wrong concentrations can damage Bermuda grass, causing widespread yellowing or patchy discoloration. Some herbicides designed for other grass types are harmful to Bermuda grass. Always read product labels, adhere to recommended rates, and consider weather conditions like extreme heat, which increase burn risk. Proper calibration of spreaders and sprayers ensures even distribution and minimizes damage.