When a healthy, green lawn suddenly begins to decline, turfgrass decline is rarely caused by a single factor. Issues fall into a few distinct categories: biological pests, microbial diseases, environmental factors, or chemical exposure. Understanding the specific patterns and signs left by each type of damage is the most reliable way to determine the correct course of action.
Diagnosing Insect Damage
Insect pests often target different parts of the grass plant, leaving behind signature signs that help distinguish their damage from other causes. Grubs are sub-surface feeders that chew directly on the root system of the turf. This root destruction starves the grass blades, causing large, irregular patches to turn yellow and then brown, often leading to secondary damage from animals like skunks or raccoons digging for the larvae. The most definitive diagnostic sign for grubs is the ability to easily lift or peel back the affected turf like a loose piece of carpet because the roots are completely severed.
Chinch bugs cause damage above the soil line by piercing the grass blades and sucking out the plant fluids. This causes the blades to yellow at the tips before the entire plant wilts. This damage frequently appears in the hottest, driest areas of the lawn, such as along sidewalks or driveways where heat is reflected. A soap drench test can confirm their presence, forcing the nymphs or adults to rise from the thatch layer.
Sod webworms are the larval stage of small moths and primarily feed at night, chewing on the grass blades near the crown of the plant. Their damage results in the grass having a ragged, unevenly mowed, or “chipped” appearance. These larvae live in silken tunnels within the thatch layer during the day. Their presence can sometimes be confirmed by noticing adult moths flying up in a zigzag pattern when walking across the lawn in the early evening.
Identifying Fungal Diseases
Fungal diseases require specific environmental conditions, typically high humidity and leaf wetness, and often leave behind distinct circular patterns or markings on the grass blades. Brown Patch appears as large, circular or semi-circular patches of brown grass. During cool, humid mornings, a defining characteristic is the presence of a “smoke ring,” a dark, grayish-brown border visible around the perimeter of the patch. This disease is often triggered by high temperatures combined with prolonged periods of leaf wetness.
Dollar Spot is characterized by small, sunken, circular patches. The infected leaves often display tan lesions with a reddish-brown margin, and the patches turn a straw color as the grass dies. This disease is frequently associated with turf suffering from low nitrogen fertility and excessive moisture on the leaf surface, often caused by watering late in the day.
Rust disease is easily recognized by the presence of yellowish to orange-red powdery masses on the grass blades. If an infected blade is wiped with a white paper towel, the orange spores will rub off, confirming the diagnosis. Rust usually occurs when grass growth is slowed due to low nitrogen levels or during extended periods of dry weather followed by high humidity.
Evaluating Water and Cultural Stress
Many issues that mimic pest or disease problems are actually related to improper maintenance practices or environmental stress. Under-watering causes the grass blades to lose turgor pressure. A simple way to check for drought stress is the “footprint test,” where footprints remain pressed into the grass because the blades lack the moisture to spring back.
Conversely, over-watering or poor drainage can suffocate the roots, causing the soil to feel spongy when walked upon. This constant saturation limits oxygen availability to the roots, leading to shallow root systems and making the turf susceptible to fungal diseases.
Improper mowing techniques, such as cutting the grass too short (scalping) or using a dull blade, place significant stress on the lawn. Soil compaction, often a result of heavy foot traffic or machinery, prevents water, air, and nutrients from reaching the root zone. A simple test for soil moisture or compaction involves pushing a screwdriver into the ground; if it is difficult to insert, the soil is likely too dry or severely compacted.
Recognizing Chemical and External Burns
Rapid, localized turf death is often the result of chemical exposure. Pet urine damage is one of the most common chemical burns, caused by the high concentration of nitrogen and salts deposited in a small area. This burn results in a distinct pattern: a patch of dead, brown grass in the center surrounded by a ring of unusually dark, vigorous green grass. The high salt content in the center dehydrates the turf to the point of death.
Fertilizer burn presents similar symptoms to urine damage. Applying an excessive amount of nitrogen-containing fertilizer over-salts the soil, drawing moisture out, resulting in a rapid browning shortly after application. This damage may appear as distinct streaks if the spreader wheels blocked the application, or as a uniform, scorched appearance across the entire lawn if the concentration was too high.
Damage from herbicides is usually identifiable by its location and shape. These burns tend to be localized to areas where the chemical was accidentally sprayed or carried by the wind. The resulting dead or discolored patches may follow straight lines, indicating a poor application technique.