Department of Crop and Soil Sciences - Cooperative Extension
Turfgrass Diseases
Yellow patch, Rhizoctonia cerealis
Yellow patch, which sometimes is referred to as cool temperature brown patch, occurs primarily on bentgrass and annual bluegrass putting greens, but may occasionally be found on Kentucky bluegrass lawns.
Symptoms and signs
On putting greens, this disease becomes visible when snow melts and appears as tan, brown, or yellow rings up to two feet in diameter. The blighted turf usually is located around the periphery of the patch, leaving healthy appearing turf in the center. Damage from yellow patch usually is superficial, but significant turf loss can occur following prolonged snow cover or during prolonged cool and wet weather in early spring. Rings may appear on high cut turf as well, but rarely cause serious damage.
Symptoms of yellow patch on creeping bentgrass putting green.
Disease cycle
Rhizoctonia cerealis oversummers as dormant resting structures and begins disease-causing activities during cool, wet weather (fall, spring, or winter) at temperatures of about 40° F. The disease frequently develops under prolonged snow cover, but does not require snow cover to produce symptoms. The fungus primarily attacks the leaf blades of turf, but can infect crowns and roots.
Cultural control
Maintaining adequate levels of soil nutrients will help turf resist severe thinning by this disease. Improved surface and subsurface drainage will aid in reducing surface moisture that provides favorable conditions for disease development. Also, timely removal of winter greens covers will help surface drying and will reduce some disease incidence. Light applications of nitrogen fertilizer in the spring will quicken turf recovery from this disease.
Chemical control
Preventative applications of broad spectrum fungicides in late fall and/or winter may help to reduce disease severity in winter or early spring.
Nematodes
Plant parasitic nematodes are small roundworms, invisible to the unaided eye, that live in the soil and on the roots of plants. They feed on the cell sap of roots by piercing the root with a spearlike mouth part similar to a hypodermic needle. Feeding by nematodes may destroy many of the feeder roots, curtailing the ability of the grass plant to obtain minerals and water from the soil. The feeding wounds produced by nematodes are used by some fungi to gain entry into the interior of the roots, causing root-decay diseases.
The majority of soil nematodes are free-living, do not possess a spearlike mouth part, and do not feed on plant roots. These beneficial nematodes feed on dead organic matter, fungi, and insects in the soil.
Symptoms and signs
Symptoms of nematode injury are similar to those associated with poor soil fertility. Nematode-infected plants exhibit these symptoms, not because the nutrients are lacking in the soil, but because the roots have been destroyed by nematodes or because the nematodes are taking nutrients needed by the plant as they feed. If soil is of satisfactory structure and texture but poor growth, off-coloring, and thinning of turf occurs and the turf does not respond to fertilization, there is a possibility that nematodes are involved.
Disease cycle
Soil in the root zones of grass plants just beginning to decline is more likely to contain parasitic nematodes than is soil around dead or nearly dead grass plants. Nematodes are easiest to detect in mid- to late summer when their populations are the highest. Accurate diagnosis of a nematode problem requires professional analysis and identification. Soil and root samples collected for nematode assay should be kept moist and cool until identification is completed. Samples collected from mid-October to May often show lower populations because the nematodes are in the egg stage and cannot be detected by normal sampling techniques.
Cultural control
Vigorous turfgrass is less likely to show damage from nematode injury. However, knowledge of the many factors influencing nematode population levels in northeastern United States is so limited that distinct cultural practice recommendations are not possible.
Chemical control
Nematicides are available as highly toxic fumigants and drenches. Chemical treatment may be undertaken only by professional pesticide applicators and only after professional diagnosis shows nematodes to be the problem.