The grass looks greener next door until you look at it from the same distance that you see your own lawn. Unless you grow it in a glass bubble, you will find weeds in any lawn grass. They come in the soil, with grass seed or on the wind from down the block. In order to get rid of those weeds in your turf, you must know how they grow.
Annual grasses grow, set seed and die within one growing season. Dave Gardner of the Ohio State University lists pre-emergent herbicides like prodiamine, dithiopyr and pendimethalin for their control. Pre-emergent herbicides are non-selective poisons that affect the ability of seeds to germinate so they should not be used on recently seeded lawns. Post-emergent herbicides are much less effective on annual grassy weeds. Smooth crabgrass, goosegrass and Johnson grass are common annual grass weeds. Large crabgrass germinates later than smooth crabgrass. The Northwest Coalition for Alternatives to Pesticide reports that corn gluten meal is effective on crabgrass. Other annual grassy weed species include barnyard grass, lovegrass, witchgrass, microstegium, crowfootgrass and green and yellow foxtail. Annual bluegrass and little barley germinate in the fall and grow throughout winter in warm-season grass areas.
Perennial grassy weeds establish clumps or crowns and put up new plants every year. They begin growing a bit later than annual weeds and are most often treated with a post-emergent herbicide containing glyphosate, a selective chemical. Quackgrass is often mistaken for crabgrass. Nimblewill, orchardgrass and timothy are other common perennial weed grasses. Rough bluegrass, one of the ancestors of today's Kentucky bluegrass, is a persistent perennial weed. NCAP reports that corn gluten controls creeping bent grass, a turf grass that can become weedy. Other potentially weedy turf grasses are Bermuda grass, creeping bent grass, centipede grass, perennial ryegrass and tall fescue; all can spread to surrounding lawn and garden areas and persist for years after eradication or replacement in their original location. Zoysia grass is another turf grass that becomes weedy; it greens up earlier and goes dormant later than other turf grasses. Purdue University's turf grass science section of the Agronomy Department reports that research is ongoing on selective controls like sulosufuron and mesotrione for weedy turf grasses that do not respond as well to glyphosate as perennial weed grasses.
Dandelion, thistle and plantain are examples of broadleaf weeds found in lawn grass. These grass weeds are opportunists; they thrive on conditions that kill lawn grass. Ground ivy (creeping Charley) flourishes in shade and knotweed grows in compacted soil. Broadleaf weeds are best controlled by treating lawn grass to the nutrients and water it needs. Post-emergent controls like 2,4-D, 2,4-DP, MCPP, and dicamba are used alone or in combinations. Many are contact systemic toxins; they must be applied when young weeds are actively growing. Other common broadleaf weeds are common bindweed, chickweed, henbit, pigweed, Jimsonweed, shepherd's purse creeping speedwell and morning glory. Clover and violets are also often treated as weeds. NCAP reports that corn gluten is effective on black nightshade, lambsquarters, creeping bentgrass, curly dock, purslane and redroot pigweed.