Annual bluegrass has always been a problem on golf courses, but has become a progressively worse problem on urban lawns. This grass is considered a weed on a homeowner's lawn for a variety of reasons. Three of the main reasons it is considered a weed are as follows. Generally annual bluegrass is a lighter green colour than Kentucky bluegrass or Fine Fescue and can cause discolouration It also has a tendency to thin out and die during summer drought conditions. This can cause areas of patching which weeds and insects will try to take advantage of. The main reason it is considered a weed is because of its seed head production. The seed head on annual bluegrass is usually higher than the Kentucky bluegrass or Fine Fescue in your lawn. This causes the lawn to appear overrun and not well maintained and looks unsightly to the homeowner. This seed head production usually occurs during May and June but can occur anytime during the growing season. Annual bluegrass is a prolific seed producer. Each plant has the ability to produce in excess of 360 seeds and the seeds can lie dormant for many growing seasons until conditions are favourable for germination. Because annual bluegrass is usually found throughout the lawn, chemical control is nearly next to impossible. Good cultural practices are your best bet when dealing with this winter annual. Annual bluegrass prefers areas that have become compacted. Aerating your lawn once a year will go a long way to alleviate this problem. Water deeply and infrequently to encourage good root development in your fescue and Kentucky bluegrass. Mow at 2 1/2 to 3 inches to discourage development of seed heads.