So, why are we talking about little barley now? Because now is NOT the time to control it unless it is in an area where a non-selective herbicide that kills everything such as glyphosate (Roundup) can be used. The best control for little barley in turf is a thick lawn that is mowed high enough that sunlight does not hit the soil. Little barley seed will not germinate in such conditions.
Overseeding in early September can thicken up a tall fescue lawn and prevent a little barley infestation. However, if you do not plan to overseed even though the lawn is a bit thin, preemergence herbicides can be used to provide at least partial control of this weed. The only preemergence herbicide that I know is labeled specifically for little barley is Surflan. It is also sold under the name of Weed Impede by Monterey Lawn and Garden.
Surflan can only be used on warm-season grasses (bermudagrass, buffalograss, zoysiagrass) and tall fescue grown in warm-season areas such as Kansas. However, Dimension (dithiopyr), is labeled for barley (Herodium spp.) which would include little barley and therefore can be used to keep this weed under control. Because little barley is a winter annual, apply the preemergence herbicide about mid-September and water in to activate. If overseeding, do not apply any preemergence herbicide as it will interfere with the germination of tall fescue. (Ward Upham)