NDSU Crop and Pest Report
Weeds


ISSUE 3  May 20, 2004

AFFECT OF FROST ON WILD OAT

Is there any practical difference in frost tolerance with wild oat vs. wheat or barley (e.g. will wild oat lose its leaves at 25 F while wheat would tolerate this temp)?

With all things being equal - there would be no difference to leaf foliage. However, wheat seedlings position their crown about 0.5 inch from the seed or relatively near the seed while wild oat seedlings position their crown about 0.5 inch from the soil surface or relatively close to the surface so if sustained frost or damaging freezing temperatures penetrates through the soil, the crown or growing point of the wild oat would be injured before deeper planted wheat and barley.

 

HERBICIDE UPDATE PART 1

Metolachlor (Several)

Mode of action: Unknown

a.i.: metolachlor

Crops: Various.

Comments: This is an example when the generic may not be equal to the original product. Stalwart C and Me-Too-Lachlor labels recommend the exact same rates as Dual II Magnum. However, their active ingredients differ in a subtle way. The first formulation of Dual and Dual II contained both isomers of metolachlor (s-metolachlor and r-metolachlor). The s- form (Dual/II/Magnum, Cinch) is about 33% more active than the r- and s- form that is in the original Dual/II formulation (2 lb ai/A of s-metolachlor = 3 lb ai/A of r- + s-metolachlor). Syngenta develop a process to deliver only s-metolachlor without the r- form thereby reducing the amount of active ingredient needed. These products are called Dual Magnum, Dual II Magnum (Syngenta) and Cinch (DuPont).

Herbicide

Ingredient

Rate

   

pt/A

lb ai/A

Dual II (Orig)

metolachlor (r+s)

2

1.95

Dual Magnum
Dual II Magnum

s-metolachlor

1.33

1.27

Cinch

s-metolachlor

1.33

1.27

Stalwart C

metolachlor (r+s)

1.33

1.3

Me-Too-Lachlor II

metolachlor (r+s)

1.33

1.3

This table shows the typical rate of Dual II Magnum is about 1/3 less than the original Dual II. These rates provide similar levels of weed control because of the greater activity of the s-metolachlor form. The Stalwart and Me-Too-Lachlor II (half r- and half s- form) labels recommend the same rates as Dual/II/Magnum, Cinch (all s- form). As a consequence the mixed r- and s- metolachlor products at labeled rates will provide less grass control than expected. Under good moisture and light weed populations, control may be fine but under heavy grass pressure and limited rainfall often found in ND, control will be reduced. Higher rates would be required to achieve the same level of control as Dual II Magnum.

These generic products should not be compared on a pint vs pint basis against Dual/II/Magnum or Cinch. Stalwart may be available but Me-Too-Lachlor may not be available in ND.

Spartan (FMC)

Mode of action: PPO Inhibitor

a.i.: sulfentrazone

Crops: Various.

Comments: Full federal Spartan registration has been approved for many crops grown in ND, including dry beans, field pea, chickpea, sunflower, potato, and mint. A 2004 Section 18 exemption has been approved allowing use on flax. The new label list rate ranges for each of the registered crops. The 2004 NDSU Weed Guide rate range for Spartan is more conservative than the federal label for some of the crops. It is recommended than growers use low rates on crops that might show temporary growth reduction and slight injury. The listing of crops from most tolerant to least tolerant is as follows: Most to least tolerant: soybean, chickpea, mint, field pea, flax, alfalfa, sunflower, potato, dry beans, corn, safflower, small grains, canola, lentil, and sugarbeet. Dry edible beans is the least tolerant of all registered crops.

A factor that greatly affects weed control and crop safety from Spartan/Authority is soil pH. The greater the soil pH the more soluble and active Spartan becomes. Use caution and always use the lowest rate allowed in high pH soils where pH is greater than 7.8. If you have not used Spartan before, it is better to use the product on a small acreage basis to determine activity, weed control, and crop safety. This is especially applies to dry beans under high pH soil.

Richard Zollinger
NDSU Extension Weed Specialist
r.zollinger@ndsu.nodak.edu


NDSU Crop and Pest ReportTop of PageTable of ContentsPrevious PageNext page