Control of Palmer amaranth (Amaranthus palmeri L.) and common lambsquarters (Chenopodium album S. Wats) with tank-mixtures of

clethodim and dicamba Andrea Rilakovic, Isidor Ceperkovic, Kasey Schroeder, Jeff Golus and Greg R. Kruger

Department of Agronomy & Horticulture, University of Nebraska-Lincoln

Introduction

• Palmer amaranth (Amaranthus palmeri S. Wats.) is aninvasive and aggressive C4 weed. It is a member of theAmaranthaceae family which is native in North America. Ithas become one of the most problematic weeds in corn,cotton, and soybean in the U.S.

• Common lambsquarters (Chenopodium album L.) is alsoone of the most problematic weeds in agriculture. Whatmakes this weed difficult to control with postemergenceherbicide is wettability and foliar uptake because of theepicuticular wax on the plant leaves surface.

• With the new dicamba-tolerant crops, it is possible thatapplicators could use tank-mixtures of dicamba and ACCaseinhibitors to control both grass and broadleaf weeds in asingle application.

Objective

• The objective of this study was to understand the efficacyof tank-mixtures of dicamba and clethodim on control ofPalmer amaranth and common lambsquarters in a doseresponse experiment with a factorial arrangement oftreatments using both herbicides.

Materials & Methods

• Two separate runs were conducted in a randomizedcomplete block design with 49 different tank-mixtures ofdicamba and clethodim.

• The plants were grown in a greenhouse.

• Plants were treated when they reached 10-15 cm in height.Each treatment had four replications with an individual plantbeing considered a single replication.

• Height between nozzle and plants was 38 cm.

• Concentrations of clethodim (0, 0.25, 0.5, 1, 2, 4 and 8X)were applied in all combinations with dicamba (0, 0.25, 0.5,1, 2, 4 and 8X) where 1X of clethodim was 0.13 kg a.i. ha ⁻¹and dicamba was 0.28 kg a.e. ha ̄ ¹.

• Visual estimations of injury were recorded at 28 d aftertreatment (DAT).

• Aboveground plant biomass was harvested 28 DAT. Plantswere dried in a forced-air drying room at 65 C for 7 d andthen weighed.

Results & Discussion

Conclusion

• The addition of clethodim (at some rates) to dicamba had an antagonistic interaction onPalmer amaranth control.

• Clethodim plus dicamba improved weed control for common lambsquarters.

• This research further shows there is not a critical dose that influences the interactionbetween clethodim and dicamba.

• Our research also demonstrates the need to have a clear understanding of the responseof the target species to tank-mixtures of clethodim and dicamba in order to optimize thecontrol of broadleaf weeds.

Figure 3. Palmer amaranth biomass reduction dose response curves for dicamba at 28 DAT with different rates of clethodim in tank-mixtures.

Figure 4. Common lambsquarters biomass reduction dose response curves for dicamba at 28 DAT with different rates of clethodim in tank-mixtures.

Number on picture: 1) Untreated control 2) 0.35 kg ha-1 dicamba3) 0.70 kg ha-1 dicamba4) 1.4 kg ha-1 dicamba5) 2.8 kg ha-1 dicamba6) 5.6 kg ha-1 dicamba7) 11.2 kg ha-1 dicamba

Figure 5. Images (from left to right) of Palmer amaranth treated with dicamba alone and dicamba plus clethodim and common lambsquarters treated with dicamba alone and dicamba plus clethodim.

Figure 1. Common lambsquarters seedlings growing in containers prior to treatment.

Figure 2. Image of the spray chamber used to apply treatments.

Table 1. Influence of different rates of clethodim on ED₅₀ and ED₉₀ values for dicamba on Palmer amaranth.

Table 2. Influence of different rates of clethodim on ED₅₀ and ED₉₀ values for dicamba on common lambsquarter.

Clethodim rate ED₅₀ SE p-value ED₉₀ SE p-value

______________________ kg ha-1 ______________________ __________ kg ha-1 __________

0 0.051 0.013075 - 0.165148 0.076738 -

0.03 0.056 0.049477 0.86957 3.708071 12.975358 0.00002

0.07 0.063 0.017800 0.46880 0.469448 0.401845 0.01123

0.13 0.057 0.017184 0.70837 0.598682 0.631465 0.08384

0.27 0.104 0.018974 0.00086 0.319015 0.142790 0.30410

0.54 0.098 0.046119 0.09899 1.159914 1.840195 0.00659

1.07 0.119 0.030352 0.00035 0.392513 0.203780 0.21338

Dicamba alone Dicamba alone 0.26 kg ha-1 clethodim 0.07 kg ha-1 clethodim

Clethodim rate ED₅₀ SE p-value ED₉₀ SE p-value

______________________ kg ha-1 ______________________ __________ kg ha-1 __________

0 1.490 2.368203 - 20.50485 56.56572 -

0.03 0.133 0.063904 0.01225 1.42988 2.21489 0.21756

0.07 0.073 0.021289 0.01370 0.58782 0.57358 0.28970

0.13 0.064 0.018027 0.03971 0.33228 0.20019 0.45582

0.27 0.099 0.312715 0.10639 12.14012 120.91377 0.71235

0.54 0.079 0.015473 0.03810 0.22043 0.10850 0.64985

1.07 0.235 0.677134 0.12261 16.11567 112.97226 0.96003