Stop Crabgrass Before It Starts Growing
Cassie Homan, Horticulture Agent
Crabgrass preventers are another name for
preemergence herbicides that prevent crabgrass seeds from developing into
mature plants. Many people have a somewhat foggy idea of how they work and
assume they kill the weed seed. Such is not the case. They do not kill the seed
or even keep the seed from germinating but rather kill the young plant after it
germinates. Therefore, they do not
prevent germination but prevent emergence.
Dimension and Barricade are the only two products
that give season-long control of crabgrass from a single application. In fact,
they can be applied much earlier than April 15th and still have sufficient
residual strength to last the season. Barricade can even be applied in the fall
for crabgrass control the next season
We recommend crabgrass preventers be applied
before fertilizer so that the grass isn’t encouraged to put on too much growth
too early. However, it may be difficult to find products that contain
preemergents without fertilizer. Those that don’t contain fertilizer are listed
below.
Weeds always seem to pop up in our lawns and
gardens no matter how often we pull them out. This year try to get ahead of the
game with a crabgrass preventer.
Crabgrass preventers are another name for
preemergence herbicides that prevent crabgrass seeds from developing into
mature plants. Many people have a somewhat foggy idea of how they work and
assume they kill the weed seed. Such is not the case. They do not kill the seed
or even keep the seed from germinating but rather kill the young plant after it
germinates. Therefore, they do not
prevent germination but prevent emergence.
Crabgrass preventers are just that – preventers.
With few exceptions they have no effect on existing crabgrass plants, so they
must be applied before germination. Additionally, preventers do not last
forever once applied to the soil.
Microorganisms and natural processes begin to
gradually break them down soon after they are applied. If some products are
applied too early, they may have lost much of their strength by the time they
are needed. Most crabgrass preventers are fairly ineffective after about 60
days, but there is considerable variation among products. (Dimension and
Barricade last longer.)
For most of Kansas, crabgrass typically begins to
germinate around May 1st or a little later. April 15th is normally a good target
date for applying preventer because it gives active ingredients time to evenly
disperse in the soil before crabgrass germination starts.
Even better, base timing on the bloom of
ornamental plants. The Eastern Redbud tree is a good choice for this purpose.
When the trees in your area approach full bloom, apply crabgrass preventer. A
follow-up application will be needed about 8 weeks later unless you are using
Dimension or Barricade. Products that do require a follow-up application
include pendimethalin (Scotts Halts) and Team (Hi-Yield Crabgrass Control).
Dimension and Barricade are the only two products
that give season-long control of crabgrass from a single application. In fact,
they can be applied much earlier than April 15th and still have sufficient
residual strength to last the season. Barricade can even be applied in the fall
for crabgrass control the next season
Dimension can be applied as early as March 1st.
Because of the added flexibility in timing, these products are favorites of
lawn care companies who have many customers to service in the spring. Though
Dimension is usually not applied as early as Barricade, it is the herbicide of
choice if it must be applied later than recommended. It is the exception to the
rule that preemergence herbicides do not kill existing weeds. Dimension can
kill crabgrass as long as it is young (two- to three-leaf stage). Dimension is
also the best choice if treating a lawn that was planted late last fall.
Normally a preemergence herbicide is not recommended unless the lawn has been
mowed two to four times. But Dimension is kind to young tall fescue, perennial
ryegrass, and Kentucky bluegrass seedlings and some formulations can be applied
as early as two weeks after the first sign of germination. However, read the
label of the specific product you wish to use to ensure that this use is
allowed. Lawns established in the fall can be safely treated with Dimension the
following spring even if they have not been mowed.
Note that products containing Dimension and
Barricade may use the common name rather than the trade name. The common
chemical name for Dimension is dithiopyr and for Barricade is prodiamine.
Remember, when using any pesticide, read the label and follow instructions
carefully.
We recommend crabgrass preventers be applied
before fertilizer so that the grass isn’t encouraged to put on too much growth
too early. However, it may be difficult to find products that contain
preemergents without fertilizer. Those that don’t contain fertilizer are listed
below.
Pendimethalin
- Scotts Halts
Team (Benefin + Trifluralin)
- Hi-Yield Crabgrass Control
Dimension
- Hi-Yield Turf & Ornamental Weed and Grass Stopper
- Bonide Crabgrass & Weed Preventer
- Green Light Crabgrass Preventer
If you would like more details about treating your lawn for weeds
contact Cassie Homan, Post Rock District Horticulture Agent, at (785)738-3597
or by email at choman@ksu.edu. Also make sure to sign up for our Lawn Care Program
on April 18. Follow this link: https://www.postrock.k-state.edu/events/
