Failure to green up in the spring or successful green-up followed by decline and death in late spring and summer is a problem that is occasionally encountered in centipede lawns. There are many factors that contribute to this problem; improper plant nutrition, cultural practices, and soil and water conditions.
The nutrient requirements of centipede are different from most other turfgrasses. An acid soil pH of 5.0 to 6.0 is preferred. As the pH goes above 6.0, iron availability decreases. Iron deficiency causes the grass to become chlorotic or yellow. A high phosphorus level also makes iron unavailable in the soil, resulting in chlorotic conditions. This is why you will see a 15-0-15 fertilizer labeled as ‘Centipede Fertilizer” since it contains no phosphorus. Centipede has a lighter green color than our other turfgrasses. It will become dark green with excessive nitrogen applications, which is the primary cause of centipede decline. Unwarranted nitrogen can also lead to thatch build-up and disease problems.
A thatch layer is an accumulation of dead plant material such as stems, stolons, and roots at the soil surface. Thatch build-up prevents water from penetrating into the soil, harbors insects and disease organisms, and leads to a shallow rooted grass that is heat, cold, and drought susceptible. New stolons grow on top of the thatch and roots don’t penetrate the soil as deeply, so the stolons and roots are exposed to cold temperatures and are more subject to drought and desiccation. If proper fertility and mowing practices are followed, grass clippings will not promote thatch build-up. A soft, spongy turf usually indicates an excessive thatch accumulation.
The following are some symptoms of centipede decline:
• The grass showing a definite yellowing or chlorosis as it greened up in the spring or when it went into dormancy in the fall. Take a soil sample for pH and fertility analysis. Look for nutrient imbalances such as low or excessive phosphorus.
• Dark green grass for most of the previous growing season. Remember that centipede is typically light green. However, as mentioned earlier, when fertilized with too much nitrogen, it will become dark green.
• The turf is easily lifted from the soil surface by pulling on the stolons. This is normally a sign of a poor root system which may be due to excess thatch, compacted soil, drought stress or nematodes. Extension offices can test for nematodes.
• When it is difficult to push a soil probe, screwdriver, or shovel in the soil. This is a sign of compacted soil.
• Grass blades turning dull green or curled up during dry weather. This is a sign of drought stress and may be due to poor watering practices, excess thatch, compacted soil, poor root development, or nematodes.
• Grass dying out in the spring or summer in a semi-circle or complete ring in an open area or around trees. Usually there is an advancing margin of dying grass along the edge of the circle during the summer. This may be caused by fairy ring fungi. If circular patches of diseased turf are observed in the spring or fall, this may also indicate take-all or large patch fungal infections.
Preventive and Corrective Measures
The previously mentioned factors may act independently or together to cause centipede decline. The following practices should help to prevent or correct the problem.
Follow proper soil preparation when planting. This is one of the most important factors. It includes soil sampling and tilling the soil which will permit better root development.
Following recommended fertilization practices. Phosphorus and lime should only be applied based on a soil test. A common mistake is to fertilize centipede too early in the spring. Wait until the soil temperature is around 70 degrees, normally about May 1. Do not overferlitize. Ideally centipede should receive only one pound of nitrogen the entire growing season, spread out at two or three applications. If the grass shows signs of iron chlorosis, apply an iron product such as ferrous sulfate or ironite. Chlororis can also be a symptom of an improper pH or elevated phosphorus.
Follow suggested cultural practices. The recommended mowing height is 1 to 1.5 inches. During the stress of summer heat, you can raise the mower one notch. Topdressing will decompose the thatch layer. Core aeration will reduce soil compaction and increase air and water movement into the soil.
Use proper watering practices. Many factors influence the amount and frequency such as soil type, fertility levels, rain, temperature, wind and humidity. Wilt in the grass is a physiological defense mechanism of the turfgrass plant. Some moisture stress actually triggers the plant to initiate rooting, allowing the grass to grow deeper in the soil. Frequent, shallow irrigation of the grass produces short roots incapable of tolerating periodic stresses. The key to good moisture management is finding the balance between some wilt and too much wilt. Actually observing some wilt within the lawn prior to watering can improve the sustainability of the turf and conserve water. Apply enough water to wet the soil to a depth of 5 to 7 inches. This is usually equivalent to 1 inch of water.