Jarrod T. Hardke

LABORATORY TOXICITY AND FIELD EFFICACY OF SELECTED INSECTICIDES AGAINST FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE) 1

ABSTRACT Fall armyworm, Spodoptera frugiperda (J. E. Smith), is an occasional but often serious pest of several row crops in the southern U.S., including cotton, field corn, and grain sorghum. The objective of these studies was to generate baseline dose-mortality responses for fall armyworm larvae in laboratory bioassays, to confirm field efficacy against natural infestations, and to determine residual efficacy of selected insecticides. These studies evaluated 4 recently developed insecticides (chlorantraniliprole, cyantraniliprole, flubendiamide, and spinetoram) and 5 commercial standards (indoxacarb, lambda-cyhalothrin, methoxyfenozide, novaluron, and spinosad). In diet-incorporated assays, the LC50 values of chlorantranilprole and spinetoram were significantly lower than the LC50s of all other insecticides. The results of a field trial against a native fall armyworm infestation in grain sorghum indicated that chlorantraniliprole reduced the number of infested whorls below that in the non-treated control and the lambda-cyhalothrin- and methoxyfenozide-treated plots at 3 d after treatment (DAT). At 7 DAT, no insecticides significantly reduced the number of infested whorls below that in the non-treated plots. In residual efficacy studies, exposure of fall armyworm larvae to chlorantraniliprole- and cyantraniliprole-treated tissue resulted in significantly greater mortality compared to those exposed to non-treated tissue and lambda-cyhalothrin-, flubendiamide-, novaluron-, and methoxyfenozide-treated tissues at 7 DAT. In addition, chlorantraniliprole and cyantraniliprole were the only compounds that resulted in >40% mortality at 28 DAT. These results indicate that newer insecticides are equal to or more efficacious against fall armyworm than traditional insecticides.

Susceptibility of Southern Green Stink Bug and Redbanded Stink Bug to Insecticides in Soybean Field Experiments and Laboratory Bioassays

Abstract Recently the redbanded stink bug, Piezodorus guildinii (Westwood), has become a major pest of soybean, Glycine max (L.) Merrill, in Louisiana and has begun to infest soybeans throughout the Mid-South. Soybean industry and cooperative extension personnel have reported differential susceptibility between the southern green stink bug, Nezara viridula L., and redbanded stink bug treated with currently labeled insecticides in commercial production fields. To address their concern, we evaluated susceptibility of southern green stink bug and redbanded stink bug to insecticides in field and laboratory experiments. Insecticide field efficacy experiments during 5 years indicated control with pyrethroids was 94.4 ± 1.3% for southern green stink bug and 75.1 ± 1.9% for redbanded stink bug, with organophosphates, 89.8 ± 2.7% for southern green stink bug, and 84.8 ± 1.7% for redbanded stink bug, and with neonicotinoid insecticides, 78.0 ± 5.6 and 63.2 ± 6.0%, respectively. Insecticide pre-mixtures or product combinations provided 98.6 ± 0.6 and 83.8 ± 2.4% control, respectively. Bioassays of adults in vials validated results in the field. Pyrethroid and organophosphate LC50 values ranged from 0.02 to 2.36 µg per vial for southern green stink bug and 0.21 to 4.86 µg per vial for redbanded stink bug. The redbanded stink bug was four to eight-fold less susceptible to pyrethroids and two to eight-fold less susceptible to organophosphates than was the southern green stink bug.

Efficacy of Dermacor-X-100® Seed Treatment Against Diatraea saccharalis (Lepidoptera: Crambidae) on Rice

Abstract The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), which attacks sugarcane, corn, sorghum, sudan grass and rice, is a major agronomic pest in the southeastern United States. This study was conducted to investigate the efficacy of different rates of Dermacor-X-100® (active ingredient, chlorantraniliprole) seed treatments on D. saccharalis in rice in the laboratory, greenhouse and field. In laboratory assays using cut stems, Dermacor-X-100® resulted in 40–50% more mortality than in the control, while in greenhouse intact plant assays Dermacor-X-100® resulted in approximately 70–80% higher mortality compared to controls. In the field study, Dermacor-X-100® seed treatment resulted in significantly lower numbers of borer entry and exit holes per plant. Results from this study suggest that Dermacor-X-100® seed treatment could be used as a valuable component of integrated pest management program for stem borers in Louisiana rice. As the boring behavior of larvae, life cycle and injury caused by most stem borers are generally similar, and because the active ingredient in Dermacor-X-100® is highly efficacious against lepidopteran pests, results for D. saccharalis may extend to management of other stem boring species as well.

Previous Crop and Cultivar Effects on Methane Emissions from Drill-Seeded, Delayed-Flood Rice Grown on a Clay Soil

Due to anaerobic conditions that develop in soils under flooded-rice (Oryza sativa L.) production, along with the global extent of rice production, it is estimated that rice cultivation is responsible for 11% of global anthropogenic methane (CH4) emissions. In order to adequately estimate CH4 emissions, it is important to include data representing the range of environmental, climatic, and cultural factors occurring in rice production, particularly from Arkansas, the leading rice-producing state in the US, and from clay soils. The objective of this study was to determine the effects of previous crop (i.e., rice or soybean (Glycine max L.)) and cultivar (i.e., Cheniere (pure-line, semidwarf), CLXL745 (hybrid), and Taggart (pure-line, standard-stature)) on CH4 fluxes and emissions from rice grown on a Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts) in eastern Arkansas. Rice following rice as a previous crop generally had greater () fluxes than rice following soybean, resulting in growing season emissions () of 19.6 and 7.0 kg CH4-C ha−1, respectively. The resulting emissions from CLXL745 (10.2 kg CH4-C ha−1) were less () than those from Cheniere or Taggart (15.5 and 14.2 kg CH4-C ha−1, resp.), which did not differ. Results of this study indicate that common Arkansas practices, such as growing rice in rotation with soybean and planting hybrid cultivars, may result in reduced CH4 emissions relative to continuous rice rotations and pure-line cultivars, respectively.

Oviposition and Sex Ratio of the Redbanded Stink Bug, Piezodorous guildinii, in Soybean.

Redbanded stink bug, Piezodorus guildinii (Westwood), is a significant soybean pest across the mid-south region of the United States. The objectives of these studies were to characterize: (1) redbanded stink bug oviposition in relationship to soybean maturity group (MG), plant structure, crop phenology, and vertical distribution within the plant canopy; and (2) redbanded stink bug adult sex ratios in relationship to soybean phenology. A total of 5645 redbanded stink bug eggs in 421 egg masses (clusters) were field collected from naturally-occurring populations in MG IV and V soybean over a three year period (2009 to 2011). The mean number of eggs within a cluster was 16.6 ± 0.3. Plant structures by MG interactions were highly significant with more egg masses oviposited on leaves in MG IV (79.4%) and more on pods in MG V (72.7%). The ratio of females to males was similar in all soybean growth stages except R5, where the sex ratio increased to 1.4:1, coinciding with peak oviposition. Only 29.9% of egg clusters in MG IV and 18.3% of egg clusters in MG V were oviposited in the upper 35 cm of the soybean canopy. Based on these results, sampling strategies and insecticide application placement for stink bugs may require modification.

Soil Physical and Chemical Characteristics Influencing Hydrogen Sulfide Toxicity

Hydrogen sulfide (H2S) toxicity is a poorly understood physiological disorder that occurs under anaerobic conditions and can cause substantial yield loss in rice (Oryza sativa L.). Though the reduction of sulfate (SO42-) to H2S is the causes of toxicity, there are many factors that influence the extent to which this occurs. Two greenhouse studies were designed to investigate the chemical and physical characteristics of four soils in Arkansas where this disorder occurs regularly (H and HR-W), sometimes occurs (HR-E), and has never been reported (PTRS). The three soils that have had this disorder (H, HR-W, and HR-E) contained approximately 30% more silt than PTRS. Mehlich 3 extractable SO42- and Fe concentrations were significantly different among the soils. In the first study, the effect of soil sterilization on SO42- concentration was examined. This study showed that SO42- concentrations over time were significantly greater in the sterilized soils from day 7-77 (p=0.0231 to <0.0001) indicating that microbes play a key role in the disappearance of SO42-. Sulfate concentrations were different from day 21-77 (p=0.0310 to <0.0001), however H and PTRS were not statistically different. Redox potential dropped more rapidly in H than PTRS, suggesting that redox potential greatly influences the occurrence of H2S toxicity. When rice was grown, there was again a statistical difference between locations (p=0.0405 to 0.0095), however H contained the most SO42- and PTRS the least. The most rapid decline in SO42- occurred after two weeks of flooding, which coincides with the onset of symptoms in the field. Within four weeks after flooding, H lost 20.7 mg SO42- kg-1 soil solution whereas PTRS lost 13.5 SO42- kg-1 soil solutions. These results indicate that the rate of SO42- reduction, decline in redox potential, and activity of microorganisms all play a role in the occurrence of H2S toxicity.

Efficacy of Rice Insecticide Seed Treatments at Selected Nitrogen Rates for Control of the Rice Water Weevil (Coleoptera: Curculionidae)

ABSTRACT Seed-applied insecticides are the standard control method used in the United States to minimize rice water weevil (Lissorhoptrus oryzophilus Kuschel) injury to rice (Oryza sativa L.) roots, and often results in greater yields than rice that receives no seed-applied insecticide. Yield increases from seed-applied insecticides often occur even when insect pressure is low and should not cause yield loss. The research objective was to evaluate the effect of urea-nitrogen rate and seed-applied insecticide on number of rice water weevil larvae, nitrogen uptake, and rice grain yield. Six trials were conducted at the Pine Tree Research Station (PTRS) and the Rice Research Extension Center (RREC) to examine the response of rice plants receiving different insecticide-seed treatments and urea-nitrogen rate combinations. Insecticide-seed treatments included label rates of clothianidin, thiamethoxam, and a noinsecticide (fungicide only) control, in combination with season-total nitrogen rates of 0, 50, 100, 150, and 200 kg urea-nitrogen/ha. Rice seed that was treated with clothianidin or thiamethoxam generally had equal numbers of rice water weevil larvae, which were significantly fewer compared with rice that received no insecticide with an equivalent urea-nitrogen rate. Nitrogen uptake at panicle differentiation was not affected by insecticide-seed treatments at four of six sites and usually increased positively and linearly as urea-nitrogen rate increased. As urea-nitrogen rate increased, grain yield increased either linearly or nonlinearly. Averaged across urea-nitrogen rates, both insecticide seed treatments had similar yields that were 4 to 7% greater than the grain yields of rice that received no insecticide at four of the five harvested sites.

EVALUATION OF SULFOXAFLOR (GF-2372) AGAINST TARNISHED PLANT BUGS IN COTTON, 2010

Insecticide efficacy trials were conducted during 2010 at the Northeast Research Station (NERS) near St. Joseph, LA (Tensas Parish) and the Macon Ridge Research Station (MRRS) near Winnsboro, LA (Franklin Parish). Cotton seed (DP 555 BG/RR) was planted into a Commerce silt loam on 25 May at NERS (trial 1) and a Gigger silt loam on 1 Jun at MRRS (trials 2 and 3). Plot size was four to eight rows (40-inches on row centers) X 50 ft with four replications. Insecticides were applied with a highclearance sprayer and compressed air system calibrated to deliver 12 GPA through TeeJet TX-10 hollow cone nozzles (2/row) at 48 psi at NERS and at 9.5 GPA through TeeJet TX-8 hollow cone nozzles (2/row) at 50 psi at MRRS. In trial 1, insecticides were applied on 20 and 29 Jul, and post-treatment evaluations were made on 3, 7 DAT1, and 2, 7, 12 DAT2. In trial 2, insecticides were applied on 3 Aug and post-treatment evaluations were made on 3, 8, 10, 14 DAT. In trial 3, insecticides were applied on 25 Aug and post-treatment evaluations were made on 3, 7, 10 DAT. Plots were sampled with a standard 2.5 x 2.5 ft black cloth shake sheet by taking two samples on two-four rows (10 row ft total) of each plot. Data were subjected to ANOVA and means separated according to DNMRT. Rainfall of 7.61, 1.46, and 0.4 inches occurred during trials 1, 2, and 3, respectively.

EVALUATION OF INSECTICIDE EFFICACY AGAINST SOYBEAN LOOPER IN SOYBEANS, 2010

A field trial evaluated selected foliar treatments against soybean looper (SBL) on R5.5 stage soybeans at the Macon Ridge Research Station (Franklin Parish). Soybean seed were planted into a Gigger-Gilbert silt loam soil on 15 Apr. Plot size was four rows (40inches on centers) X 45 ft. Treatments were arranged in a RCB design with four replications. Insecticides were applied with a highclearance sprayer and compressed air system calibrated to deliver 6 gpa through TeeJet TX-8 hollow cone nozzles (2/row) at 50 psi. Insecticides were applied on 13 Aug, and post-treatment evaluations were performed at 3, 7 and 11 DAT. Insecticide efficacy was measured by taking 25 sweep-samples with a sweep net (15 inches diameter) in each plot and recording the number of SBL larvae > 1⁄2 inch. Data were subjected to ANOVA and means separated according to DNMRT. Total rainfall of 0.76 inches occurred during the trial period.

EVALUATION OF SELECTED INSECTICIDES FOR CONTROL OF HELIOTHINES IN BT AND NON-BT COTTON, 2006

Three field trials evaluated control of heliothines on cotton in Jefferson County, AR. Cotton seed (Deltapine cultivars) were planted across the test areas on 16 May. Plot size was four rows (38-inches on centers) X 50 ft. Treatments were placed in a RCB design with four replications. Insecticides were applied with a John Deere 6500 Hi-Cycle and compressed air system calibrated to deliver 9.69 GPA through TeeJet TXVS-6 hollow cone nozzles (2/row) at 45 psi. Insecticide efficacy was measured by randomly selecting 25 samples each of terminals, flower buds (squares), blooms, and bolls. The number of damaged structures and the number of structures with surviving larvae were recorded in each plot. In the first trial (Table 1), insecticides applied to plots of a non-Bacillus thuringiensis (Bt) cotton (DP 434RR) and compared to a Bollgard II cotton (DP 117 B2RF) cultivar and non-treated plots of DP 434RR. Insecticides were applied on 10 Jul, and post-treatment evaluations were made on 13, 19 Jul; and 2 Aug. In the second trial (Table 2), insecticides were applied to a Bollgard cotton (DP 444 BGRR) cultivar on 31 Jul and plots were evaluated on 3, 7 Aug. In the third trial (Table 3), insecticides were applied to a nonBt cotton (DP 434 RR) cultivar on 10, 20 Jul, and 1 Aug, and plots evaluated on 13, 17, 24, 31 Jul; 3 Aug and 9 Aug. Rainfall did not influence treatment efficacy in these trials.