The increase in herbicide-resistant weeds over the past decade has led to the introduction of crops that are resistant to auxin herbicides. Strict application procedures are required for the use of auxin herbicides in auxin-resistant crops to minimize off-target movement. One requirement for application is the use of nozzles that will minimize drift by producing coarse droplets. Generally, an increase in droplet size can lead to a reduction in coverage and efficacy depending upon the herbicide and weed species. In studies conducted in 2015 and 2016, two of the potential required auxin nozzle types [(AIXR11002 (coarse) and TTI11002 (ultra-coarse)] were compared to a conventional flat-fan drift guard nozzles [DG11002 (medium)] for weed control in peanut herbicide systems. Nozzle type did not influence annual grass or Palmer amaranth control in non-crop tests. Results from in-crop tests indicated that annual grass control was 5% to 6% lower when herbicides were applied with the TTI nozzle when compared to the AIXR or DG nozzles. However, Palmer amaranth control and peanut yield was not influenced by coarse-droplet nozzles. Peanut growers using the coarse-droplet nozzles need to be aware of potential reduced grass control.
The introduction and mass adoption of glyphosate resistant crops in the late 1990's led to the reliance of glyphosate alone as a weed control method in many instances (
One concern with applying auxin herbicides in current production systems is the sensitivity that many other plant species have to these herbicides (
Herbicide efficacy can be directly related to droplet size but also can differ greatly depending on herbicide and weed species being controlled (Mckinlay
Auxin-resistant technologies will likely be widely adopted by growers. In 2016, 43% of the cotton ha in the Southeastern United States were planted to dicamba-resistant cultivars (
Peanut has long been an important rotational crop with cotton for Georgia growers due to its many benefits, such as reduced disease and insect pressure, decreased/easier to manage weed pressure, and its ability to provide nitrogen to the soil (
Weed control research has been conducted on the effect of nozzle type and droplet size on individual herbicides and herbicide tank-mixture efficacy (
A non-crop study was conducted during 2015 and 2016 at the Ponder Research Farm located near Ty Ty, Georgia (31.5076540N, -83.6583950) on a Tifton loamy sand soil with 93% sand 3% silt, 4 % clay, 1% organic matter, and pH of 6.0. The trial was arranged in a randomized complete block design with a 4 by 3 factorial arrangement of treatments. Four herbicide treatments and 3 nozzle types were used. The herbicide treatments were as follows: Non-treated control (NTC); paraquat (0.21 kg ai/ha) plus bentazon (0.37 kg ai/ha) plus acifluorfen (0.19 kg ai/ha) plus
Plot size was 7.6 m by 0.9 m. Each treatment was replicated 3 or 4 times depending upon field availability. Palmer amaranth and a non-uniform mixture of annual grasses including, Texas millet (
An in-crop trial was also conducted at the Ponder Research Farm and the Attapulgus Research and Education Center (30.7636290N, -84.4799380) on a Faceville loamy sand with 84% sand, 10% clay, 6% silt, 1.6% organic matter, and pH of 6.0 during 2015 and 2016 (4 site-years). Conventional tillage practices were used and 'Georgia-06G' (
The trial was arranged in a randomized complete block design with a 4 by 3 factorial design (4 herbicide programs and 3 nozzle types) with 4 replications. The herbicide programs presented in
Herbicide program, active ingredient, rate, and timings for in-crop/peanut nozzle studies, 2015-2016.
University of Georgia Extension peanut production recommendations were used and supplemental irrigation was applied to maximize peanut growth and development (
Soil type, planting dates, application dates, peanut stages of growth, weed heights, and harvest dates for in-crop/peanut nozzle studies in Georgia, 2015-2016a.
Data for all parameters in both the non-crop and in-crop studies were analyzed as factorial plot designs and subjected to ANOVA using the PROC MIXED procedure in SAS (SAS Institute 107 Inc., Cary, NC 27511). Nozzle type and herbicide treatment/program were considered fixed effects and locations and replications (nested within year) were considered random effects. No treatment by location and herbicide/program by nozzle interactions were significant (P ≥ 77), therefore data were combined over locations and only treatment main effects are presented. Least square means of significant main effects were separated using pairwise t-tests (alpha=0.10).
When data were pooled over the four herbicide treatments, nozzle type had no effect on the control of Palmer amaranth and a non-uniform mixture of annual grasses (
Influence of nozzle type on weed control (non-crop study) in Georgia, 2015-2016a
At 7 and 14 DAT, Palmer amaranth control with imazapic + 2,4-DB +
Influence of herbicide treatment on weed control (non-crop study) in Georgia, 2015-2016abc.
Nozzle type had no effect on peanut injury (
Influence of nozzle type on peanut weed control programs and yield in Georgia, 2015-2016a.
Herbicide program effects on peanut weed control and yield in Georgia, 2015-2016ab.
Palmer amaranth control, when averaged over all four herbicide programs, was not significantly influenced by nozzle type at any rating date (
Herbicides applied with the TTI11002 nozzle which produced the coarsest droplet of the nozzles evaluated, were 5 to 6% less effective at controlling annual grasses at both rating dates than the AIXR and DG nozzles (
Peanut yield was not affected by nozzle type or herbicide program (
In summary, growers who use coarse-droplet producing nozzles for weed control in auxin tolerant crops should not have to change nozzles for weed control in peanut when Palmer amaranth is present. In some instances, annual grass control may be slightly reduced when TTI nozzles are used. It is also important to note that these trials were conducted under irrigated conditions and results could differ in non-irrigated or dryland production systems. Additional nozzle performance data is needed for other troublesome weeds in peanut including sicklepod (
The technical support of Charlie Hilton, Dwayne Dales, Timothy Richards, and the Attapulgus Research and Education Center is greatly appreciated.
Graduate Research Assistant and Professor and Extension Weed Specialist, respectively. Dept. of Crop & Soil Sciences, The University of Georgia, Tifton, GA 31793.
Agricultural Research Statistician, The University of Georgia, Griffin, GA 30223.