HELPFUL HINTS HELPFUL HINTS
HELPFUL HINTS
FROM THE LAWN INSTITUTE FROM THE LAWN INSTITUTE
FROM THE LAWN INSTITUTE GRASSY WEED CONTROL
Tere are many species of grassy weeds that can be found in home lawns and other turfgrass sites. Like all plants, they can have various life cycles, growth habits, and features that make them easier, or more difficult to control. Tere are fundamental differences between grassy and broadleaf weeds and some grass-like weeds are not grasses at all. Tey are sedges, rushes, or even broadleaf weeds that simply appear to be grass-like. Understanding key differences in features of each of these types of plants is important in controlling them successfully.
Grassy weeds are monocots with leaves that emerge alternately after germination, as opposed to oppositely (in pairs) like broadleaf weeds. Tey have hollow stems and leaves that emerge in a rolled or folded fashion from the sheath. Unlike broadleaf weeds, they have parallel veins that run the length of each leaf making them easy to distinguish from broadleaf weeds which have netted veins. One could almost say that if it looks like a grass, then it is likely a grass. Although, sedges, rushes, and even some dicots have long narrow leaves that can be mistaken for grasses.
Proper identification is extremely important in grassy weed control, because unlike herbicides for broadleaf weeds that control a wide-spectrum, many grassy herbicides only control a handful of grassy weeds. Furthermore, when trying to control a grassy weed in a grass lawn there are many sensitivities that can cause injury to desirable grasses. As a result, not only is it important to know the grassy weed species you are trying to control, it’s important to properly identify the lawn grass as well.
Grassy weeds are most effectively controlled with pre- emergence herbicides that control the weeds immediately after they germinate but before they emerge through the
For more information on lawn care and helpful “How to” tips, visit The Lawn Institute at:
www.TheLawnInstitute.org.
TPI Turf News November/December 2019 9
turfgrass canopy, hence the name pre-emergence. Grassy weeds are more easily controlled during this life stage and grass lawns are generally much more tolerant of pre- emergence herbicides than they are of post-emergence herbicides. Also, grasses are prolific seed producers so it is important to get them before they germinate in order to break the life cycle. Annual grasses such as goosegrass, crabgrass, annual bluegrass, etc. are successfully controlled with herbicides containing pendimethalin, prodiamine, dithiopyr, atrazine, simazine, and oxadiazon. Tese products will control a wide range of grasses at the pre- emergence stage but if allowed to mature there are fewer products that will control them.
Mature perennial grassy weeds are often the most difficult to control. Weeds such as dallisgrass and common bermudagrass cannot be controlled with pre-emergence herbicides after they are already present at which point there are fewer options and increased likelihoods for injury to the desirable grass. Perennial grassy weeds often have storage organs including rhizomes and stolons that can store vast amounts of energy deep in the canopy or underground that allow them to recover from herbicide applications. As a result, herbicides often result in visible injury but most, if not all, take repeated applications to fully kill the weed.
Be sure to apply pre-emergence herbicides before germination and split applications can be helpful under high weed pressure. With post-emergence herbicides, do not apply when the lawn is under heat or drought stress and do not mow 2-3 days before or after application. As always, follow labeled directions and use these products judiciously.
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