Annual bluegrass invades desirable turfgrasses each fall in the sourthern
states. Annual bluegrass is a particularly serious weed problem in closely
mowed areas such as golf greens and fairways.
Description. Two types of Poa annua are found in the southern states - an upright growing plant with a bunch-type growth pattern and a decumbent type with creeping stolons. The upright type is a prolific seed producer and is an annual. The decumbent type produces very little seed and is perennial in nature although it dies during the summer in the deep South.
Annual bluegrass begins to emerge in late summer and early fall when night temperatures are in the 60's and moisture is abundant. Annual bluegrass seeds continue to germinate through the fall, winter and spring - a characteristic that makes chemical control more difficult.
Germination and growth of annual bluegrass are favored by moist soil conditions and cool temperatures. Thus, it has a strong competitive advantage over warm season grasses from fall through spring. On closely mowed and irrigated turf, annual bluegrass will dominate a stand of bermudagrass by late spring if herbicides are not used. Populations of annual bluegrass are greatly reduced by taller mowing heights and limited use of water. Thus, we find little annual bluegrass in golf course roughs, lawns, parks and other areas maintained at taller mowing heights and with less irrigation.
Annual bluegrass initiates seedheads in late fall and winter, but seedhead development is greatest in the spring and early summer. Until those seedheads appear, annual bluegrass is not too objectionable. After seedhead appearance, the turf develops a yellowish-white color and an uneven appearance.
Control. Annual bluegrass can be effectively controlled with pre- and post-emergence herbicides in warm season turfgrasses. Preemerge products must be applied prior to the emergence of annual bluegrass in the fall. The date of emergence varies between locations and years, but generally begins when night temperatures are in the 60's and daytime temperatures are below 85°F. Where winter grasses are to be overseeded on bermudagrass turf, applications of preemergence products must be made 60 to 90 days before seeding. Follow label directions for all products.