Experiments were conducted in 2016 and 2017 in Stoneville and Starkville Mississippi to determine the impact of different insecticide management options for thrips on herbicide injured peanut. Insecticide treatments included imidacloprid in-furrow at-planting, one or two foliar applications of acephate, and an untreated control with and without an application of flumioxazin. In Stoneville, herbicide applications were made immediately following planting, and in Starkville, applications were made as plants were emerging to maximize herbicide injury. The Stoneville experiment also had an additional factor in which plots were flooded or not flooded to simulate a heavy rainfall in order to maximize herbicide injury and also to give added stress from saturated soils. Thrips counts, thrips injury ratings, plant vigor ratings, plant biomass, width between plant canopies, and yield were recorded. Few interactions were observed, but temporary flooding, herbicide injury, and thrips injury affected peanut growth as measured by biomass and canopy. Imidacloprid was the most consistent insecticide treatment for reducing thrips numbers and injury, but acephate provided some protection. Temporary flooding during the seedling stage, flumioxazin injury, and thrips injury all reduced peanut pod yield. Based on these results, every attempt should be made to minimize early season stress in peanuts including the use of an effective in-furrow insecticide.
Peanut (
At-planting soil insecticides are the primary control option for managing thrips in peanut. Previous research has shown that in-furrow treatments can reduce first generation thrips larvae by 70-95%, resulting in less feeding injury (
Herbicide resistant weeds are an increasing problem in all crops. Currently, 23 different weed species in the mid-south US are resistant to certain classes of herbicides (
An experiment was conducted at the Delta Research and Extension Center in Stoneville, MS in 2016 and 2017. The soil at this location consisted of a Beulah very fine sandy loam (Coarse-loamy, mixed, active thermic Typic Dystrudepts,
Treatments were arranged as a split-split-plot within a randomized complete block design with four replications. The main-plot, sub-plot, and sub-sub-plot factors included flood irrigation at two levels, herbicide application at two levels, and thrips management at four levels, respectively. The main plot factor of flooding included flooded and not flooded. The flooding factor was included to simulate a heavy rainfall event that would cause water ponding and maximize herbicide injury. Flooding treatments were imposed within two d after peanut emergence. Levees were erected around the exterior of the flooded plots with an implement commonly used in rice production (levee plow). Smaller levees were also constructed in the alleys between each replication to ensure sufficient flooding. Surface water was pumped from a nearby creek through 30.5-cm diam. poly-ethylene tubing. Water was held on plots in each replication for 30 minutes to maximize injury. Replications were flooded individually before breaching the levee between replications. This allowed water to flow into plots of the next replication until all were flooded separately. One week after flooding, levees were removed. The sub-plot factor of herbicide included a preemergence application of flumioxazin at a rate of 0.163 kg ai/ha or no flumioxazin. Flumioxazin (Valor® EZ, Valent U.S.A., LLC, Walnut Creek, CA) was applied with a tractor mounted sprayer with a compressed air system calibrated to deliver 140 L ha−1 at 296 kPa through 8004 flat fan nozzles immediately after planting. The sub-sub-plot factor of thrips management included imidacloprid (Admire® Pro, Bayer CropScience, Raleigh, NC) sprayed into the open seed furrow at 0.36 g ai ha−1 at-planting, one foliar application of acephate (Acephate 90 WDG, Loveland Products, Loveland, CO) at seven d after flooding, two foliar applications of acephate at 7 and 14 d after flooding, and an untreated control. The in-furrow imidacloprid treatment was applied with a nozzle attached to the planter positioned over each seed furrow immediately in front of the closing wheels. The application volume was 46.7 L ha−1 at 138 kPa through an 8002 flat fan nozzle. The flat fan nozzle was oriented parallel to the open seed furrow. This resulted in the entire spray pattern being directed into the open seed furrow to insure optimum coverage of the seed furrow and the seed. All foliar applications of acephate were made at a rate of 0.55 kg ai/ha. Foliar applications were made with a self-propelled sprayer (MudMasterTM, Bowman Manufacturing, Newport, AR) with a compressed air system calibrated to deliver 93.3 L ha−1 through TX-6 hollow cone nozzles at 241 kPa.
The size of each sub-sub-plot was four rows (102-cm row spacing) that were 12.2-m in length separated by 3.05-m unplanted alleys. Plots were planted on 06 May, 2016 and 10 May, 2017 at a seeding rate of 21 seeds per row m. The cultivar used for this experiment was Georgia-06G (Birdsong Peanuts, Suffolk, VA). A peanut inoculant (
Treatments for the experiment in Starkville were similar to Stoneville, except they were arranged as a split-plot within a randomized complete block design with four replications. The flooding factor was not included at this location because a levee plow was not available. The main plot factor was herbicide application at two levels. This included an application of flumioxazin at a rate of 0.163 kg ai ha−1 or no flumioxazin. Because the flooding factor was not included in this study, flumioxazin was applied when plants began to emerge instead of preemergence in order to maximize herbicide injury. The sub-plot factor was thrips management at four levels identical to the treatments of the Stoneville experiment. The size of each sub-plot was four rows (96.5 cm row spacing) 9.14 m in length separated by 3.05 m unplanted alleys. Plots were planted 06 May 2016 and 11 May 2017 with the same cultivar and seeding rate used in the Stoneville experiment.
Thrips populations were sampled 10 and 17 d after plant emergence (8 and 15 d after flooding in Stoneville) by cutting five random plants at the soil surface from each plot and placing them into 0.95-L self-sealing plastic bags (Ziploc®, S. C. Johnson & Son, Inc., Racine, WI). These timings corresponded to one day after the acephate foliar applications made at 7 and 14 d after flooding, respectively. Plants were washed using a whole plant method developed for cotton (
Thrips injury was estimated two d after the second insecticide application by visually examining the center two rows of each plot. These ratings were adapted from thrips injury ratings used on cotton (
Plant biomass was recorded 34 d after planting by randomly removing five plants from each plot and placing them in paper bags. Paper bags were placed in a greenhouse and allowed to air dry for two weeks. Upon drying, plants were weighed on an analytical laboratory balance (Mettler-Toledo AL54, Mettler-Toledo, LLC, Columbus, OH). Width between plant canopies was measured 45 and 60 d after planting. This was defined as the width between the outermost vines of plants on rows two and three. Five locations per plot were measured by placing a m stick between the vines on these two rows and then averaged.
Digging dates were determined by the hull scape maturity profile method to determine plant maturity (
Combined thrips counts (adults plus immatures), thrips injury ratings, herbicide injury ratings, plant biomass, width between canopies, and yield data were analyzed with a mixed model analysis of variance (PROC GLIMMIX, SAS 9.4, SAS Institute Inc. Cary, NC). Flooding (Stoneville only), herbicide, insecticide, and their interactions were considered fixed effects in the model. Locations were analyzed separately because the experimental arrangement was different at each location. Year, replication nested in year, and replication by herbicide nested in year were considered random effects in the model. Degrees of freedom were calculated using the Kenward-Roger method. Means and standard errors were calculated with PROC MEANS. Means were separated using LSMEANS and adjusted using the Tukey method for separation. Differences were considered significant at α=0.05.
There was no interaction between flooding, herbicide, and insecticide for any of the variables measured (
Results of the analysis of variance for thrips numbers and damage, herbicide injury, plant growth, and peanut yields as impacted by flooding, herbicide use, and insecticide use for an experiment conducted in Stoneville, MS during 2016 and 2017.
Impact of insecticide treatment on thrips numbers and damage, plant growth, and peanut yields in Stoneville, MS averaged across 2016 and 2017.
In terms of plant growth, flood and insecticide had an impact on plant biomass (
There was a significant effect of flood, herbicide, and insecticide on peanut pod yields (
Insecticide was the only factor that impacted thrips populations at the first sample date (
Results of the analysis of variance for thrips numbers and damage, plant growth, and peanut yields as impacted by herbicide use and insecticide use for an experiment conducted in Starkville, MS during 2016 and 2017.
Impact of insecticide treatment on thrips numbers and damage and plant growth in Starkville, MS averaged across 2016 and 2017.
For peanut growth, there was an effect of herbicide and insecticide on canopy coverage at both rating periods, and an effect of insecticide on biomass (
For peanut pod yields, there was an herbicide by insecticide interaction. Pod yield of peanut plants grown with one foliar application of acephate and plants grown with imidacloprid applied in the seed furrow at planting was greater than pod yield for untreated peanuts where flumioxazin was not applied (
Early season biotic and abiotic stressors can limit yield in multiple cropping systems. Injury from the use of flumioxazin for preemergence weed control reduced pod yield at the Stoneville location. At the Starkville location, flumioxazin was applied at the cracking stage instead of preemergence and little injury was observed, but pod yield was still lower than where flumioxazin was not used. Previous research suggests that flumioxazin rarely causes yield losses in peanut when applied preemerge (
In general, use of an insecticide for thrips management resulted in fewer thrips, less thrips injury, and increased plant vigor than where no insecticides were used. This was expected as similar results were observed in previous research (
At the Stoneville location, the flumioxazin-treated plots had more injury from thrips than plots with no herbicide. This was not observed in the Starkville experiment where flumioxazin applied at cracking resulted less injury than that observed in Stoneville. The additional stress from flooding resulted in plants incurring more injury in the flooded plots than the unflooded plots which may have also had an effect on thrips injury. Flooding, which moved the flumioxazin onto the plants from the soil surface increased herbicide injury and further delayed seedling development, which may have rendered plants more susceptible to thrips injury.
Use of an insecticide resulted in more vigorous plants compared to those in plots with no insecticide application across all years at both the Stoneville and Starkville locations. Flooding and flumioxazin use had negative effects as plants were not able to grow as vigorously as uninjured plants. In a non-flooded environment, there was no difference in vigor whether there was a flumioxazin application or not.
In general, plants with an insecticide treatment had greater biomass and faster canopy closure compared to the untreated control. Flumioxazin use created adverse growing conditions for plants, which in turn resulted in less biomass and slower canopy closure. Like flumioxazin and thrips injury, flooding also had a negative effect on biomass and canopy closure in Stoneville. Canopy closure is important in peanut production for weed control. The narrower the width between canopies of adjacent rows, the more likely weeds are to be shaded out and not able to become established. Similarly, the incidence of tomato spotted wilt virus has been shown to be reduced with thicker plant canopies and in twin-row production systems (
In regards to yield, significant differences were only observed in the experiment in Stoneville. Any insecticide application resulted in a significant yield increase compared to the untreated control. Flumioxazin caused a yield decrease in the Stoneville experiment, however, this what not observed in Starkville. Flooding during the seedling stage also resulted in lower yields of peanut. Previous research has shown thrips injury, herbicide injury, and saturated soils can have adverse effects on yield (
No interaction between flumioxazin use, flooding, and insecticide use, was observed. However, each factor individually effected peanut growth and yield. With herbicide resistant weeds becoming more of a concern, choosing not to make a preemergence application of flumioxazin could result in yield reduction due to competition from weeds. Insecticide applications early in the growing season could result in greater yields. Insecticide applied at-planting are recommended to manage thrips, preserve plant vigor, expedite canopy closure, and preserve yield. Inoculant is already being applied in-furrow at the time of planting, so co-applying imidacloprid is a less expensive option than making one or two foliar applications of acephate after plant emergence. Foliar application of acephate is an option if additional stress from thrips needs to be alleviated. Additionally, more research is needed to determine the best herbicide options for a preemergence program that maximize weed control and minimize plant injury.
The authors thank the Mississippi Peanut Promotion Board, Mississippi Peanut Growers Association, and Cotton Incorporated for partial funding of this project. This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch project under accession number 1003452.
First, second, fourth, and fifth authors: Graduate Student, Research Professor, Associate Research Professor, Assistant Extension Professor, Delta Res. & Ext. Center, Mississippi State Univ. Stoneville, MS 38776; Third and eighth author: Extension Professor and Graduate student, Dept. of Biochemistry, Molecular Biology, Entomology, & Plant Pathology, Mississippi State University, Mississippi State, MS 39762. Sixth, seventh (formerly), and ninth authors, Dept. of Plant & Soil Sciences, Mississippi State Univ., Mississippi State, MS 39762