Biological control of annual bluegrass

Tradi t ional weed control in agric u l t u r e ha s b e e n a c c o m p l i s h e d primarily through the use of chemical herbicides and cultivation. Cultivation practices are of little use for weed control in turfgrass management. Turf managers, therefore, tend to rely heavily on chemicals for weed control. Chemical herbicides tend to exhibit rather broad spectrum characteristics. Two common examples are 2,4-D and glyphosate (Roundup, Rodeo, etc.). The advantage of such broad spectrum activity is that, for example, with 2,4-D many broadleaf weeds will be affected by one chemical. In the case of glysophate, virtually all plants will be affected, making this a very important renovation tool. The d i sadvan tages of broad spec t rum chemicals is that non-target plants may be affected. A slight gust of wind can carry that herbicide to some landscaping trees or shrubs, putting an end to the tender loving care that was needed to properly establish these plants at the site. A n o t h e r d i s a d v a n t a g e is tha t weeds from the same family or group of plants as the desirable propagated plant cannot be controlled without also harming the desirable plants. Very few chemicals exist that are species or cultivar specific. It is precisely this characteristic that makes annual bluegrass (Poa annua) the most important weed problem on golf courses, lawns and other turfgrass sites. No chemicals currently exist that can se lec t ive ly e l imina te annua l bluegass from desirable Kentucky bluegrass (Poa pratensis) and creeping bentgrass (Agrostís palustris). The problem is compounded by the fact that, whereas annual bluegrass seeds will normally be controlled by a pre-emergence herbicide, annual bluegrass also occurs as a perennial (Poa annual var. reptans). Clearly an effective control is needed because the annual bluegrass component of many lawns and golf courses exceeds 50 percent of the grass species.