I wish to follow up last week's article and discuss the factors that affect the performance of Newpath herbicide in Clearfield rice.
First, let's consider the soil-applied treatments. There are basically two ways to make a soil application — preplant incorporated or pre-emergence.
A preplant incorporated treatment needs to be thoroughly mixed into the top 2 or 3 inches of the final seedbed. The treatment is only applicable to conventional seedbed systems and realistically only on the silt loam and lighter soils. Trying to incorporate on a clay soil usually results in moisture loss and clod rolling.
When you thoroughly incorporate a herbicide such as Newpath into a nice, moist, clod-free seedbed, you can get excellent early weed control without rainfall for activation. When it works properly, it is a very nice treatment.
I am not aware of any incorporation research that has been conducted in recent years. However, most research available, going all the way back to the early Treflan days, shows that with the exception of power-driven tools such as a tiller, optimum incorporation requires two passes.
Most final seedbed preparation that I observe is done with a field cultivator and most of it is single pass and usually only about to the depth of planting.
There are some nice tools out there that make an excellent seedbed with one pass. However, they can still result in streaking and very shallow incorporation of the herbicide.
The best incorporation results from a field cultivator are achieved with two passes with the second at some angle to the first.
In addition to streaking resulting in some escapes with incorporated treatments, soil moisture will vary. There may be enough moisture down in the seedbed to get a stand, but the upper portion may be dry enough to allow red rice escapes.
With an incorporated treatment, two incorporation passes are better than one and rolling will break clods and help hold in moisture.
Ultimately though, if rainfall does not occur by emergence, a flush will be required to maintain performance.
A pre-emergence herbicide is applied to the soil surface after planting but before emergence. This is the only practical way a soil-applied herbicide can be used in a no-till or stale seedbed system or on the heavy clay soils.
This is the least consistent way to use Newpath. First, if a soaking rainfall does not occur prior to red rice emergence, failure results if the field is not flushed.
Most growers are reluctant to flush prior to rice emergence unless it is not going to emerge without it. Even in those cases, deep emerging red rice will emerge before the field is flushed for a stand.
Another thing that can cause a pre-emergence herbicide to fail even with rainfall is the presence of heavy residue in a no-till system or large clods on a clay soil. Even when things are ideal, the performance of a pre-emergence herbicide can be disappointing.
From the very earliest research we conducted in Clearfield rice, I was surprised by the results comparing preplant incorporated versus pre-emergence treatments. In most of your studies we would prepare the seedbed, incorporate the preplant treatments, plant the plots, spray the pre-emergence treatments, and flush the plot area immediately.
I initially thought that under these conditions, a pre-emergence treatment would outperform the preplant incorporated treatment. The result was consistently the opposite. The incorporated Newpath treatments would outperform the pre-emergence treatments by 10 to 20 percent, even with immediate flushing.
While the soil-applied treatments can perform nicely under ideal conditions, when they fail they fail miserably. The result is often the red rice emerging untouched and then overpowering the remaining postemergence treatment.
I looked at far too many fields last year where this happened. Next week I will cover the postemergence treatments.
Ford Baldwin, Practical Weed Consultants. e-mail: email@example.com.