Graduate Research Associate, Professor, Professor and Professor, respectively. Department of Crop & Soil Sciences, The University of Georgia, 2360 Rainwater Drive, Tifton, GA 31793;
Assitant Professor, Crop, Soil and Environmental Sciences, Auburn University, Funchess Hall, Auburn, AL 36345
Weed control is an integral part of peanut (
Georgia is the leading producer of peanut (
The critical period of weed control for peanut is from 3 to 8 wk after planting. This makes postemergence (POST) herbicide applications important and necessary to avoid irreversible yield loss (
Bentazon acts as a safener by reducing both paraquat injury on peanut and efficacy on susceptible weed species (
Peanut producers in Georgia have become interested in using a liquid fertilizer replacement for bentazon in their paraquat POST tank-mixtures. Specifically, Ele-Max® Nutrient Concentrate (inorganic liquid nutrient [ILN]) (Helena Chemical Company, Colliervile, TN, 38017), is an 11-8-5 (N-P2O5- K2O) with ethylenediaminetetraacetic acid (EDTA) chelated micronutrients (B, Fe, Mn, Cu, Zn, Co, and Mo) (
Two separate experiments were conducted, one managed with supplemental irrigation and one rainfed. The first location was the University of Georgia (UGA) Southwest Georgia Research and Education Center (SWREC) in Plains, GA (32.0468, -84.3662, which had a Greenville sandy loam (fine, kaolinitic, thermic Rhodic Kandiudult) soil with 3.8% organic matter (OM), 60% sand, 10% silt, and 30% clay. The second location was the UGA Attapulgus Research and Education Center in Attapulgus, GA (30.7608, -84.4870, which had an Orangeburg loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudult) soil with 1.5% OM, 86% sand, 6% silt, and 8% clay. Soil pH was 6.0 and 5.6, respectively. In 2016, only the irrigated field experiment was conducted at the UGA Attapulgus Research and Education Center, while both the irrigated and non-irrigated field experiments were conducted at the UGA SWREC. In 2017, the irrigated and non-irrigated field experiments were conducted at the UGA SWREC only.
All trial sites were prepared by disc harrowing, moldboard plowing (30 cm deep), followed by rotary-tillage. Beds were 1.8 m wide (2 rows per bed). Plot length varied by site and year due to differing field dimensions for the given site-year. In Attapulgus plot length was 7.6 m. At the SWREC, plot length in 2016 was 12.2 m while it was 9.1 m in 2017. Peanuts were planted in two single rows (90 cm spacing) on 2 May 2016 in Attapulgus, and 16 May 2016 and 2 May 2017 at the SWREC. Planting was done using a two row Monosem air planter (Monosem-Inc., Edwardsville, KS) at 19 seeds/m of row to a depth of 5 cm. Georgia-06G (
The trial was arranged as a 4 by 2 factorial (four levels of herbicide treatments and two levels of ILN treatments) in a randomized complete block design (RCB) with four replications. The herbicide treatments were paraquat (0.21 kg ai/ha) plus nonionic surfactant (0.25% v/v), paraquat (0.21 kg ai/ha) plus
Data collection included visual injury and stunting ratings of 0 (none) to 100% (complete necrosis/death), vegetative biomass (g/plant), peanut pod biomass (g/plant), peanut pod yield (kg/ha), and grade (total sound mature kernels % [TSMK]). Visual estimates of foliar injury (chlorosis/necrosis) were evaluated at 3, 7, 11, and 14 d after treatment (DAT). Visual stunting was measured at 3, 7, 11, 14, 21 and 28 DAT. Peanut plant biomass data was collected at the V8, R2, and R7 to R8 growth stages (
Peanut maturity was determined by the hull scrape method (
Analysis of variance (ANOVA) was conducted for all response variables using PROC MIXED in SAS 9.4 (SAS Institute Inc., Cary, NC, 27513). Preliminary analyses were performed on all response variables to measure the effects of site-year as a fixed effect. Independent variables were site-year, herbicide, and ILN. Significant interactions were detected between site-year and treatments for response variables and were the result of magnitude of differences among treatments but with similar trends of response across site-year. Subsequent analyses were done for all data combined across site-year. Herbicide, ILN, and their interactions were considered fixed effects, while site-year and replication were considered random effects. Irrigated and non-irrigated experiments were analyzed separately. Pairwise comparison of least square means for all response variables were made using the Tukey's honestly significant difference test (𝜶=0.05) (
Greenhouse trials were conducted at the UGA Tifton Campus-Coastal Plains Experiment Station in Tifton, Georgia. This experiment evaluated the phytotoxic effects and efficacy of ILN in POST tank-mixtures with paraquat on multiple weed species. Large crabgrass (
This experiment was conducted as a RCB design with a split-plot restriction on randomization with four replications. The experiment was repeated twice in time during 2017. Herbicide treatments (flats) were the whole plot factor while weed species (cells) were the subplots. Herbicide treatments included paraquat (0.21 kg ai/ha) plus nonionic surfactant (0.25% v/v), paraquat (0.21 kg ai/ha) plus
Weeds were treated at the 2-3 true leaf stage. All applications were made using a moving belt sprayer calibrated to spray 187 L/ha at 3 kph. Visual estimates of injury (same scale previously described) for chlorosis/necrosis were evaluated at 3 and 7 DAT. Above ground biomass (% of the control) was measured at 7 DAT after the visual injury ratings were recorded. Above ground re-growth biomass (% of the control) was collected 14 d after the initial biomass harvest. ANOVA was conducted for all response variables using PROC MIXED in SAS 9.4 (SAS Institute Inc., Cary, NC, 27513). Replication was treated as a random effect while weed species and herbicide treatment were treated as fixed effects. Data were combined over iteration. Pairwise comparison of least square means for all response variables were made using the Tukey's honestly significant difference test (𝜶=0.05) (
Herbicide by ILN interactions were detected for leaf burn at 3 DAT and stunting at 3 and 28 DAT (
For leaf burn, herbicide injury was greatest at 3 DAT. However, there were no differences among herbicides at 7 DAT (
Across all ratings, paraquat plus
Herbicide by ILN interactions were present for leaf burn at 3 DAT and stunting at 3 and 14 DAT (
At 3 DAT, there were no differences among herbicide treatments for peanut leaf burn ranging from 20 to 25%, but all were greater than the NTC (
For stunting, paraquat plus
Herbicide by weed species interaction was significant for all parameters except for regrowth biomass (
ILN alone did not cause any significant leaf burn across all weed species when compared to the NTC at 7 DAT (
For biomass, ILN alone was not significantly different from the NTC across all weed species (
Our results indicated that there were similar trends in chlorosis/necrosis (%) among weed species. All herbicide treatments without acifluorfen plus bentazon were not different for large crabgrass, Florida beggarweed, pitted morningglory, bristly starbur, and sicklepod. At 7 DAT, adding
To determine if ILN could be used as a replacement for bentazon in tank-mixture with paraquat, we compared the paraquat plus
The irrigated and non-irrigated studies showed similar trends in injury (leaf burn and stunting) levels. Paraquat plus
Overall, including ILN in tank-mixture only slightly reduced peanut injury up to 7 DAT but had no impact on injury after one week. ILN also had no effect on yield or grade for both irrigated and non-irrigated peanut. Additions of ILN improved the control of sicklepod and prickly sida but did not improve the control of large crabgrass, Florida beggarweed, bristly starbur, Palmer amaranth, and pitted morningglory.
While the addition of ILN to the various paraquat tank-mixtures initially reduced injury, it did not correspond to increases in yield or grade. The variability in weed control, transient injury mitigation, and no yield increase indicates that Georgia peanut growers will receive no benefit for including ILN in their paraquat tank-mixtures but if needed to improve crop nutrition, ILN will not reduce weed control.
This research was supported by the National Peanut Board and the Georgia Peanut Commission. The authors would like to thank Wen Carter, Kristen Pegues, Sidney Cromer, and Nick Hurdle for technical assistance. Seed was donated by the Georgia Seed Development Commission. This project was also supported as part of Federal Hatch project #GEO00273.
Graduate Research Associate, Professor, Professor and Professor, respectively. Department of Crop & Soil Sciences, The University of Georgia, 2360 Rainwater Drive, Tifton, GA 31793;
Assitant Professor, Crop, Soil and Environmental Sciences, Auburn University, Funchess Hall, Auburn, AL 36345