Nematodes

Nematodes may cause serious damage on some turfgrasses growing in very sandy soils in the Eastern and sandhills regions of the state. Turf affected by nematodes usually appears weak and thin. It may have symptoms of nutrient deficiencies or wilts rapidly during dry weather. Similar symptoms may be caused by other problems such as poor fertility, lack of moisture and some diseases. Root stunting, excessive branching and even death of roots may occur with some nematodes. These symptoms are not usually adequate to identify nematodes as the major problem, therefore, soil samples must be assayed for nematodes. Also, a soil fertility test is recommended to eliminate nutritional problems as a major factor.

Nematodes are small eel-like worms that are too small to be seen without a microscope. Nematodes that attack plants have small needle-like stylets which are used to puncture plant cells to obtain nutrients. Different nematode species that attack turfgrasses cause root stunting, death of roots, knots on roots and some cause no apparent harm even at high numbers. Nematodes usually do not kill the host plants, but they do increase damage from other stresses, such as drought.

Nematodes that are found most frequently in soil from turfgrasses are ring, stunt, spiral, lance, stubby-root and sting. Only the sting and the stubby-root nematodes have been shown to cause severe damage on turfgrasses in research projects at North Carolina State University. The sting nematode is known to be the most damaging nematode and frequently occurs in the sandy soils of eastern and south central North Carolina. It is difficult to grow good quality turfgrasses where this nematode is present.

Nematicides are not currently labeled for the control of nematodes on turfgrasses in home lawns. Good turf management practices must be used in place of nematicides in home lawns to grow healthy turfgrasses that can tolerate some nematode damage. Some organic soil amendments, such as shrimp and crab shells, may encourage fungi that kill nematodes. Incorporation of organic matter in the soil before planting will help the soil increase antagonistic microorganisms and help grow healthier turfgrasses. High rates of organic matter should be used carefully on centipedegrass because too much nitrogen may be released and cause excessive growth that would result in decreased drought and cold tolerance.

Some management practices can be used to help minimize the damage from nematodes. The use of good fertilization programs to insure proper levels of nutrients, irrigation to supply adequate soil moisture, and recommended cutting heights will help turfgrasses tolerate certain levels of damaging nematodes. In some cases an alternative turfgrass may be considered. For example, centipedegrass is more susceptible to the sting nematode than bermudagrass or bahiagrass . Therefore, bermudagrass would be the best choice for use in residential lawns where high quality turf is desired if irrigation is available. Zoysiagrass has been observed to be very sensitive to damage from sting nematodes and would not be a good replacement for centipedegrass in sting nematode infested soil. Bahiagrass may be the best choice for lower quality lawns and in large commercial lawns in eastern North Carolina. Very little damage from nematodes has been observed on this course textured grass.

Nematode management practices must be incorporated into lawn management systems where nematode damage occurs. This approach will offer new challenges to turf managers and homeowners since chemicals are no longer available to control nematodes in residential lawns.

Soil Compaction

Compaction from construction or traffic (walking, vehicles, playing or animals) may result in poor growth of turfgrasses. Proper oxygen and water relations in the soil are disrupted by compaction. The soil should be loosened by renovating or coring to relieve the compaction for better growth of turfgrasses.

High Soluble Salts

Too much fertilizer or the use of irrigation water high in salts can damage turfgrasses. Too much salt in the soil does not allow the roots to take up sufficient amounts of water or will draw water from the roots. Damage from very high rates of fertilizer can be seen in a few days. Evaporation and use of water in the soil by the turfgrass plants during dry weather can concentrate soluble salts to the point that damage may occur. Proper amounts of fertilizer should be distributed evenly over the lawn. Care should be taken to avoid spills or overlapping of fertilizer. Soluble salt damage from too much fertilizer may be in streaks or spots from uneven application, whereas damage from salts in animal urine will be in small circular spots. Irrigation to keep the soil moisture at proper levels can prevent soluble salts from reaching damaging levels during dry weather. If high levels of soluble salts are detected in the soil, extra irrigation or long periods of rain are needed to leach the salts deeper into the soil. The warm-season grasses usually will recover from short exposures to high soluble salts, but the cool-season grasses may be killed.

Animal Urine

High soluble salts and nitrogen levels in animal urine can damage turfgrasses. Grasses may be killed in small circular spots 1/2 to 1 foot in diameter. The surrounding grass becomes greener and cool-season grasses become clumpy or weeds invade the dead areas. Warm-season turfgrasses that spread by stolons and rhizomes may be killed in spots; however, these grasses will usually spread into the affected areas quickly. Dark green spots with taller grasses usually remain for several weeks. The damage to turfgrasses is caused by the high soluble salts from the urine and the greening is caused by nitrogen-containing compounds in the urine. The effects can be reduced by irrigating to leach the salts deeper into the soil. Grasses such as tall fescue should be replanted in the spots before weeds become established.

Fairy Rings

Fairy ring symptoms are large circular dead spots, dead rings, or green rings (3 to 20 feet in diameter) that enlarge for several years. Mushrooms of the fungi that cause this problem may be present at the edge of the rings or throughout the circles sometime during the year. Mushrooms may not develop for several years and suddenly appear following a weather pattern that induces mushroom development. Effective treatments are not known for fairy rings in lawns, however, rototilling the soil and replanting healthy grass has eliminated the problem in some cases.

Slime Molds

Slime molds appear as gray to black growths in small circular patches on leaves of turfgrasses. These growths are fungi that are slimy in wet weather that develop into a powdery mass of spores a few days later. Slime molds cause very little damage to turfgrasses. Some damage may occur if the fungal growth is heavy enough to cause shading of the affected leaves. The fungi can be removed by brushing, washing, or mowing the affected leaves. Broad spectrum fungicides can be used to control slime molds if large areas are affected and the turf becomes unsightly.

Algae

Algae are single-celled plants that grow on the surface of wet soils. Algae may appear as a black slimy growth on the surface of a poorly drained soil in wet weather and may crack and curl when the soil becomes dry. It is usually a problem in an area that does not drain properly and may have a low soil pH. Algae can be controlled by correcting soil drainage and soil nutrient problems.

Moss

Lawns with too much shade, low soil pH and low nutrient levels may have problems with moss. Mosses are short, light green to brownish plants that grow in shady areas. Removal of excess shade and application of fertilizer and lime as recommended from a soil test will help turfgrasses grow in areas with mosses. Moss may be an alternative to grasses if the area has very little traffic and if a low maintenance landscape is desired.

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