Friday, May 2, 2008

Turf - Perennial Grass Weeds in Cool Season Turf

Undesirable perennial grasses in turf-type tall fescue include coarse pasture varieties of tall fescue such as KY31, orchardgrass (Dactylis glomerata), rough bluegrass (Poa trivialis), and creeping bentgrass (Agrostis palustris). The following is an article on the subject.

Pasture types of tall fescue will be coarser, more bunching, and taller, with wider leaves than turf varieties. Orchardgrass is a coarse pasture grass. It can be distinguished by its flattened sheaths, blue-green color, and leaf blades 1/4 to 1/2 inch wide. It grows in bunches and is upright. Rough bluegrass is a perennial bluegrass that spreads by stolons and seed. Leaves are light green, 1/8 inch wide, with the typical boat-shaped tip of bluegrasses. The seedhead is a panicle similar to other bluegrass species. It is larger that annual bluegrass, growing in patches, and can be differentiated by the presence of stolons. Creeping bentgass has blue-green leaves that are flat, 1/8 inch wide, with pointed tips and prominent veins. Seed heads are purplish, compressed panicles occurring in mid spring. It spreads by vigorous stolons and forms dense patches of fine-textured grass. These perennial grasses are introduced from contaminated seed sources, plants in seed at adjacent sites, or seed carried by mowers, workers, and equipment.

Unfortunately, there currently are no registered postemergence selective herbicides for the control of these perennial grass weeds in turf-type tall fescue for residential lawns, recreation areas, or commercial turf areas. Small patches of bunch grasses such as pasture-type tall fescue and orchardgrass should be dug out with a shovel and then the holes filled and reseeded. For larger infested areas, spot application of non-selective glyphosate herbicide is recommended for control followed by reseeding. Control of the spreading grasses, rough bluegrass and creeping bentgrass, is accomplished by two or more sequential applications of glyphosate followed by reseeding after full control. This may take several months. Applications should be made to young, fully green, actively growing plants that are not under stress. For severely infested turf, complete renovation of the whole area with multiple applications of glyphosate followed by reseeding may be required.

A new herbicide was be registered in 2008 for use in turf called Tenacity. It contains mesotrione as the active ingredient and will be an excellent selective control for creeping bentgrass in turf-type tall fescue. However, it is only labelled for golf courses and sod farms. If the label is expanded, we will inform you.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County.

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