Tuesday, March 15, 2011

Rejuvenating Turf in 2011: Part II

Part II: Preemergence and postemergence herbicides for crabgrass control in newly seeded areas
This turf tip is part of a three part series on spring seeding.

Early spring preemergence herbicides are often necessary in Indiana to prevent troublesome annual grassy weeds such as crabgrass and goosegrass. Additionally, these applications help to prevent the emergence of some broadleaf weeds. Most preemergence herbicides work to kill weeds by preventing cell division causing death to weed seedlings shortly after they germinate. All preemergence herbicides (except Tupersan) work to prevent the emergence of turfgrass seeds as well as weed seeds, so do not reseed areas treated with a preemergence herbicide this spring or do not apply a preemergence herbicide if you plan on seeding.

How to control crabgrass in lawns this spring

There are five potential options.

Control crabgrass as normal with a preemergence herbicide (dithiopyr, prodiamine, or pendimethalin) because the turf is not severely damaged and thin areas will fill-in from Kentucky bluegrass rhizomes. NOTE: If the lawn is tall fescue or perennial ryegrass it will not fill-in thin areas without additional seeding.

Tupersan (siduron) may be used for preemerg­ence control of annual grassy weeds in newly seeded cool-season turf and zoysia­grass. Check the label for rates and use directions. This herbicide is more expensive and short-lived, but it is the only safe preemergence herbicide to apply at the time of seeding.

Another strategy is to use a postemergence herbicide instead of a preemergence herbicide to control crabgrass in late May and June that is safe to use on seedling turf. Options include Drive (quinclorac), Tenacity (mesotrione), and SquareOne (quinclorac + carfentrazone). These products can be most safely used very soon after seeding to control crabgrass (see label for exact details on each turf species). If the seedlings are more mature (have been mown 2-3 times following their emergence) then other products such as Q4 Plus (quinclorac + sulfentrazone + 2,4-D + dicamba), Onetime (quinclorac + MCPP + dicamba), or Solitare (quinclorac + sulfentrazone) can also be used. For homeowners, there are now several products that contain quinclorac which can be used. Look for quinclorac in the list of ingredients on the label. NOTE: Tenacity (mesotrione) mentioned above can be used on all turf areas except residential home lawns at the time of this writing; however, a residential lawn label is anticipated for this product in the spring of 2011.

A fourth option is to use Dimension (dithiopyr) in May after a spring seeding to control newly germinated crabgrass that has emerged and is still at the 1-2 leaf stage or just started tillering. Dimension is the only preemergence herbicide which has good postemergence activity on newly germinated crabgrass. This application would also prevent future crabgrass germination through the rest of the summer in newly seeded areas. Another modification of this strategy would be to tank mix Barricade (Prodiamine) or Pendulum (Pendimethalin) with a post-emergence crabgrass product like Acclaim Extra (fenoxaprop), Drive (quinclorac), other quinclorac containing products, or Tenacity (mesotrione) in order to get both preemergence and postemergence control of crabgrass in a newly seeded area. The assumption with all of these herbicide options in this scenario is that the seedlings were planted in early spring and that they have developed enough of a root system to tolerate an application of a preemergence herbicide in May.

The last option is to go ahead and apply a preemergence herbicide to control crabgrass despite the fact that the lawn may be thin and in need of seeding. Since establishing turf in the spring is not as optimal as establishing turf in the late summer (mid-August to mid-September), you might likely have better long term results if you wait to seed in the fall as opposed to seeding this spring. This will only be an option for those patient enough to wait until they get their lawn back into shape.

Aaron Patton, Assistant Professor/Turfgrass Extension Specialist


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