TO CONTROL WEEDS

WEED CONTROL

Several products have been released in recent years that give

superintendents new options for control of difficult weeds.

Several new herbicide formulations or active

ingredients have been released for use in turf during

the past few years. In addition, several experimental

compounds with considerable promise

should be released within the next couple of years.

The emergence of these new herbicides has highlighted

three major trends (Table 1).

Selectivity. Many of these materials promise to

allow the superintendent selectivity, particularly

with perennial grass weed control, that we would

not have thought possible even five years ago.

These new herbicides are Velocity (bispyribacsodium,

Valent USA), Tenacity (mesotrione, Syngenta)

and Certainty (sulfosulfuron, Monsanto).

Single-application weed control. Another trend

is that there are many formulated products, either

newly released or in various stages of testing, that

offer "single application" weed control. That is,

they control both crabgrass and broadleaf weeds.

Q4 (PBI/Gordon) and Quincept (NuFarm Amerj

icas) are examples of products intended to control

all weeds post-emergence with a single applica-

tion. Both combine 2,4-D, dicamba and quinclorac

(the active ingredient in Drive [BASF]). Q4

also contains sulfentrazone and thus has activity

on yellow nutsedge (see below).

Quinclorac is not new, but BASF has released

a new formulation, and quinclorac is now appearing

in combination products, not just for crabgrass

control, but also for broadleaf weed control,

particularly clover. Several other combination

products that will afford pre- and post-emergence

control of broadleaf and grassy weeds with one

application are in various stages of testing.

Granular herbicides. Another emerging trend

is that granular herbicide technology seems poised

to improve considerably in the next few years.

One reason for this improvement is the development

of more herbicides that are active in soil and

therefore more effective when superintendents are

relying on take-up from the soil. Another reason

is that formulation improvements in granules are

increasing the amount of contact between the

herbicide and the foliage.

Mesotrione

Mesotrione, the active ingredient of a new

herbicide introduced by Syngenta under the trade

name Tenacity, controls perhaps the widest weed

spectrum of any herbicide used in turfgrass. It has

been available in agriculture for many years and

has a very distinctive mode of action: By inhibiting

carotenoid pigment synthesis, it bleaches the

affected tissue, which turns the target weed white.

Tenacity: a very broad spectrum

Research conducted at Ohio State and other

institutions over the past few years suggests that

Tenacity will have many uses in turfgrass management,

including pre- and post-emergence activity

on dandelion, white clover, crabgrass, nimblewill,

creeping bentgrass and orchardgrass.

As a broadleaf weed herbicide, Tenacity has

good activity against dandelions and fair activity

against clover. A unique property of this herbicide

is that it benefits from or requires a second

application in order to control certain weeds. One

application results in suppression of the weed, followed

by regrowth in about 42 to 56 days.

Dandelion is, however, an exception. Research

at Ohio State suggests that two applications of

mesotrione do not provide significantly better

control than one application. In either case, control

is about 70%-85% and can be increased by

combining Tenacity with another herbicide. Our

research indicates that Tenacity has better activity

when combined with either dicamba or the

pyridinoxy herbicides Spotlight (fluroxypyr, Dow

Aherbicide introduced by Syngenta under the trade

name Tenacity, controls perhaps the widest weed

spectrum of any herbicide used in turfgrass. It has

been available in agriculture for many years and

has a very distinctive mode of action: By inhibiting

carotenoid pigment synthesis, it bleaches the

affected tissue, which turns the target weed white.

Tenacity: a very broad spectrum

Research conducted at Ohio State and other

institutions over the past few years suggests that

Tenacity will have many uses in turfgrass management,

including pre- and post-emergence activity

on dandelion, white clover, crabgrass, nimblewill,

creeping bentgrass and orchardgrass.

As a broadleaf weed herbicide, Tenacity has

good activity against dandelions and fair activity

against clover. A unique property of this herbicide

is that it benefits from or requires a second

application in order to control certain weeds. One

application results in suppression of the weed, followed

by regrowth in about 42 to 56 days.

Dandelion is, however, an exception. Research

at Ohio State suggests that two applications of

mesotrione do not provide significantly better

control than one application. In either case, control

is about 70%-85% and can be increased by

combining Tenacity with another herbicide. Our

research indicates that Tenacity has better activity

when combined with either dicamba or the

pyridinoxy herbicides Spotlight (fluroxypyr, Dow

Agrosciences) or Turflon ester (triclopyr, Dow

AgroSciences) (Figure 1).

One important note is that our research also

suggests that Tenacity does not combine well with

either Quicksilver (carfentrazone, FMC Corp.) or

Dismiss (sulfentrazone, FMC Corp.) for broadleaf

weed control. Tenacity also has activity on clover.

However, this is more suppression than control,

particularly if only one application is made. When

combined with pyridinoxy herbicides or dicamba,

white clover control is improved.

Research conducted at Ohio State suggests that

when Tenacity is used as a pre-emergence herbicide,

it may achieve 100% control of crabgrass for

160 days. However, some researchers have found

it a bit less effective; check the label for specifics.

In addition, our research suggests that mesotrione's

post-emergence activity on crabgrass is at

least as good as, and occasionally better than, that

of quinclorac.

The dandelion, clover and crabgrass control

are nice bonuses. What I consider the most useful

attributes of this product are its selective activity

on weedy perennial grasses and its safety on seedling

turfgrass.