Will a Dicamba-Resistant Waterhemp be Resistant to 2,4-D (and vice versa)?

Feb 16, 2021

By Dr. Bob Hartzler

Reliance on synthetic auxin herbicides (HG 4) has increased following the introduction of dicamba and 2,4-D resistant soybean. A common question among users of these products is: “If I use one trait repeatedly and select for resistance to that herbicide, will I be able to switch to the other trait to control the resistant population?”

I did a quick, non-comprehensive literature search for papers that evaluated cross-resistance to 2,4-D and dicamba (Tables 1 and 2). Biotypes that were selected by one of the herbicides had cross-resistance to the other in about 50% of the situations. In most cases where cross-resistance occurred, the level of resistance (R:S) was lower to the herbicide not responsible for selection than for the herbicide that selected the resistance (i.e. a population selected by repeated 2,4-D use had a lower level of resistance to dicamba than to 2,4-D).

Cross Resistance to dicamba

Numerous mechanisms are known to provide resistance to synthetic auxin herbicides, including insensitive target sites, enhanced metabolism, and altered translocation. The specific mechanism found in a weed probably influences the likelihood of cross-resistance. Several populations of waterhemp and Palmer amaranth resistant to synthetic herbicides have been identified in soybean producing states. While cross-resistance between 2,4-D and dicamba is not a given, it occurs frequently enough to reinforce the need for integrated management to sustain the value of these herbicides.

Source : iastate.edu

Video: Winter Canola Trial in Mississippi | Can It Work for Double Cropping? | Pioneer Agronomy

Can winter canola open new opportunities for growers in the Mid-South? In this agronomy update from Noxubee County, Mississippi, Pioneer agronomist Gus Eifling shares an early look at a first-year winter canola trial and what farmers are learning from the field.

Planted in late October on 30-inch rows, the crop is now entering the bloom stage and progressing quickly. In this video, we walk through current field conditions, fertility management, and how timing could make this crop a valuable option for double-cropping soybeans or cotton.

If harvest timing lines up with early May, growers may be able to transition directly into another crop during ideal planting windows. Ongoing field trials will help determine whether canola could become a viable rotational option for the region.

Watch for:

How winter canola is performing in its first season in this Mississippi field

Why growers chose 30-inch rows for this trial

What the crop looks like as it moves from bolting into bloom

Fertility strategy, including nitrogen and sulfur applications

How canola harvest timing could enable double-cropping with soybeans or cotton

Upcoming trials comparing soybeans after canola vs. traditional planting

As more growers look for ways to maximize acres and diversify rotations, experiments like this help determine what new crops might fit into existing systems.