Thursday, November 15, 2007

Nursery - Weed Control in Field Grown Nurseries

The following is some information on weed control in field grown nurseries from a presentation by Dr. Stephen Hart at Rutgers

Weed management challenges in field grown nurseries are:
  • Year round weed control is required
  • There is a lack of crop competition with weeds (not a lot of shading)
  • Tillage is only done at establishment normally
  • These are perennial crops so perennial weeds are often a problem
  • There is a wide diversity of plants being produced so no one herbicide program will fit all
  • There is a relatively small number of herbicides registered

Programs rely on preemergence herbicides with low water solubility and long residual and spot treatments of non-selectives for perennial weed control and annual escapes. Often extensive labor is needed, especially for post spot herbicide applications.

Major weed problems are summer annual grasses and broaleaf weeds with marestail becomming more of an issue (due to glyphosate resistance) and morningglory due to its late season germination. Perennial weed problems include yellow nutsedge, mugwort, bindweeds, and Canada thistle.

Preemergence herbicides that are extensively used extensively according to chemical class are:

  • Dinitroanalines: Pendimethalin (Pendulum), prodiamine (Factor, Barricade), trifluralin (Treflan), oryazalin (Surflan). These give annual grass control and some small seeded broadleaf control and have good safety across ornamental species.
  • Acid Amides: Metolachor (Pennant Magnum) is the main one in this group. Pennant provides nutsedge and grass control. It is labelled mainly on woody species.
  • Triazines: Simazine (Princep) is the main herbicide used in this group. It has annual broadleaf and some grass control. It is low cost. It is limited to woody ornamentals.
  • Diphenylethers: Some of the most effective nursery herbicides fall into this class which includes oxyfluorfen (Goal), oxadiazon (Ronstar), and flumioxizon (SureGuard and Broadstar). This group controls annual broadleaf weeds and some annual grasses.
  • Others: Isoxaben (Gallery) is the main one here. It is an annual broadleaf weed material. It is safe on a wide range of ornamentals including many herbaceous perennials but is relatively high cost.

Selective postemergence nursery herbicides for nurseries include the grass products sethoxydim (Vantage), fluazifop (Fusilade), and Clethodim (Envoy) that are save on most ornamentals (except ornamental grasses). There are only a few postemergence broadleaf materials for nurseries. Chlopyralid (Lontrel, Stinger) is the main one and is very limited in the species it can be used on.

Non selective herbicides for postemergence spot weed control mainly include the glyphosate products (Roundup and many others) and Finale. Finale is mainly used for control of weeds that glyphosate does not work well on. This includes glyphosate resistant marestail and morningglory. One issue with Finale is that it can cause bark splitting.

Where they are labelled, SureGuard/Broadstar and Goal have provided superior annual weed control in field grown nurseries in spring applied programs. Pennant Magnum is often added to give grass and nutsedge control. In fall applications, the grass materials would be Pendulum, Factor, Surflan, or Devrinol mixed with the broadleaf materials SureGuard/Broadstar, Princep, or Gallery. Goal is not recommended for fall due to lack of marestail activity.

Summarized by Gordon Johnson, Extension Agriculture Agent, UD, Kent County

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