You’ve tried removing weeds by hand and preventing them with
mulches and landscape fabrics. Your last line of defense is
chemical control.

If you’re not opposed to using herbicides, a large array of them
are available. In fact, so many are on the garden center shelves
that many people get confused.

Much of the confusion comes from the fact that many herbicides
are no longer patented, so any company that wants to can sell
them. Some of the many brands you might recognize are Ortho,
Spectracide, Bonide, Dragon, Hi-Yield and Acme. As if that
weren’t enough, most herbicides, but not all, come in both
granular and sprayable forms.

Think ‘Active Ingredients’

If you keep track of the name and percentage of active
ingredients, you can shop around among brands to get the best
buy.

There’s no difference in the active ingredients except the
percentage and possibly the formulation. The diquat in a Ortho
product is the same diquat in a Spectracide brand.

That doesn’t mean all products are the same. Some sprays have
different surfactants or wetting agents. And different materials
in granular forms can affect the herbicide release rate. These
factors can affect a brand’s ability to control weeds.

More Herbicide Terms

Other herbicide terms to keep clear are selective, nonselective,
pre-emergent and postemergent.

If a herbicide is selective, it will control some plant species
and not others. Ornamec, for example, controls only grasses. A
nonselective herbicide controls any vegetation that it is applied
to. A good example is Roundup, which can kill any plant it comes
in contact with.

Pre-emergent herbicides control weeds that originate from seed
and haven’t yet germinated. They rarely work on perennial weeds
that germinate from bulbs, corms, rhizomes, stolons or other
vegetative structures.

Their active ingredients include dichlobenil, prodiamine,
isoxaben, pendimethalin, metolachlor, trifluralin, simazine,
oxadiazon and oryzalin. Some control only a few tough weeds. Most
control various ranges of annual grasses and broadleaf weeds.

Postemergent herbicides’ active ingredients include bentazon,
triclopyr, clethodim, glufosinate, halosulfuron, fluazifop,
diquat, glyphosate, sethoxydim or potassium salts of fatty
acids.

These products generally control actively growing grasses or
other emerged annual weeds, including tough weeds like purple and
yellow nut sedge and some woody plants.

A few products can be both pre- and postemergent.

Mode-of-Action

Mode-of-action is a term homeowners probably won’t see but should
be aware of. A herbicide’s MOA, or the specific way it works,
is usually understood, but now always.

For example, glyphosate (Roundup) makes plants unable to make key
proteins and enzymes, so they starve to death. But we don’t fully
understand how dichlobenil (Casoron or Norosac) works.

There are many restrictions on the uses of both pre- and
postemergent herbicides. Some can be applied over the top of
actively growing ornamentals, for instance, and some can’t.

Follow Directions

For this reason, it’s wise to read the directions provided with
the herbicide. Precisely following the label can keep you from
damaging landscape plants or wasting costly herbicides.

If you’re unsure about appropriate uses or have questions about
herbicides, contact your county Extension Service agent.

Here are some herbicides homeowners commonly use. They don’t
require a licence when used on your own property. Their active
ingredients can be sold alone or in combination with other
herbicides.

Pre-emergent Herbicides

• Casoron and Norosac (dichlobenil) control many tough
  weeds,
  such as Florida betony and horsetails, in many established woody
  ornamentals. Use them only in the late fall, winter or early
  spring. They can provide postemergent control of some weedy
  plants.

• Factor, Barricade and others (prodiamine) control many
  annual grasses and small seeded broadleaf weeds.
• Gallery and others (isoxaben) control many annual
  broadleaf
  weeds. Isoxaben provides poor control of annual grasses but
  provide excellent pre-emergent control when mixed with other
  herbicides like Surflan.
• Pendulum (pendimethalin) controls many annual grasses
  and
  small seeded broadleaf weeds.
• Pennant (metolachlor) controls many annual grasses and
  small-seeded broadleaf weeds. Pennant provides some pre-emergent
  activity on yellow nut sedge.
• Preen and Treflan 5G (trifluralin), have a
  weed-control
  spectrum like that of Surflan. If possible, apply them before
  planting, under mulch, and incorporate into top 1 to 3 inches of
  soil.
• Princep (simazine) controls many annual grasses and
  small-seeded broadleaf weeds.
• Ronstar and others (oxadiazon) controls many annual
  grasses
  and small-seeded broadleaf weeds.
• Surflan (oryzalin) controls many annual grasses and
  small-seeded broadleaf weeds. Excellent tank-mixed with
  Roundup.