Aerial application methods control spider mites on corn in Kansas, USA.

The Banks grass mite, Oligonychus pratensis (Banks), and two-spotted spider mite, Tetranychus urticae Koch, are important chelicerae herbivores on irrigated corn in Kansas, USA. They cause loss of foliage, stalk breakage, kernel shrinkage and yield loss. Aerial application methods were evaluated to control spider mites in a commercial corn field in August, 2017, near Hoxie, Kansas. Dimethoate (0.56 kg active ingredient/ha) and Lorsban Advanced (1.05 kg active ingredient/ha) mixed with a nonionic surfactant, Traverse (0.25% v/v), were aerially applied using conventional flat-fan hydraulic nozzles at 28.1 L/ha and aerial electrostatic nozzles at 9.3 L/ha. To assess spray droplet spectra of the aerial application methods, water sensitive paper samplers were deployed at the whorl of husk leaves at the tip of the ear before aerial spray treatments were applied. Spray droplet spectra were quantified using commercial image analysis software. Treatment efficacy was assessed both objectively and subjectively. Objective efficacy evaluation incorporated the use of an active multispectral optical sensor via spectral analysis of the midrib regions of corn leaves on the abaxial surface where spider mites reside. Subjective damage ratings based upon in-field spider mite movement observations were scored by professional crop scouting consultants. Results of objective spectral analysis and subjective damage ratings indicated that both the conventional and electrostatic nozzles with 283 and 210-µm spray droplet 'volume median diameter' (VMD) at 28.1 and 9.3 L/ha, respectively, controlled spider mites compared to an untreated check.

Active optical sensor assessment of spider mite damage on greenhouse beans and cotton.

The two-spotted spider mite, Tetranychus urticae Koch, is an important pest of cotton in mid-southern USA and causes yield reduction and deprivation in fiber fitness. Cotton and pinto beans grown in the greenhouse were infested with spider mites at the three-leaf and trifoliate stages, respectively. Spider mite damage on cotton and bean canopies expressed as normalized difference vegetation index indicative of changes in plant health was measured for 27 consecutive days. Plant health decreased incrementally for cotton until day 21 when complete destruction occurred. Thereafter, regrowth reversed decline in plant health. On spider mite treated beans, plant vigor plateaued until day 11 when plant health declined incrementally. Results indicate that pinto beans were better suited as a host plant than cotton for rearing T. urticae in the laboratory.

Evaluation of selected acaricides against twospotted spider mite (Acari: Tetranychidae) on greenhouse cotton using multispectral data.

Twospotted spider mite (TSSM), Tetranychus urticae Koch, is an early season pest of cotton in the mid-southern USA and causes reduction in yield, fiber quality and impaired seed germination. Objectives of this study were to investigate the efficacy of abamectin and spiromesifen with two divergent LC50 values against TSSM in a computer-operated spray table which simulated aerial application parameters. Combined with a pressure of 276 kPa and a speed of 8 km/h, a 650033 nozzle delivered a spray rate of 18.7 L/ha. The active ingredient rates were 1/8, 1/4, 1/2 and the lowest label recommended rates for early season cotton. The intent was to study efficacy relative to deposition characteristics at active ingredient rates equal to and lower than those recommended by the label. Spectral reflectance values from a multispectral optical sensor were used to calculate the Normalized Difference Vegetation Index which numerically described the surface reflectance characteristics of cotton canopies concomitant to damage caused by T. urticae in the greenhouse. Water sensitive paper samplers described spray droplet spectra parameters (Dv0.1, Dv0.5 and Dv0.9, µm) and percent spray coverage. The volume median diameter (Dv0.5, µm) for abamectin and spiromesifen were respectively, 218 and 258 at one-half rate of the lowest label rate. These spray droplets were well above the driftable portions of the spray volume (<141 µm) for both abamectin and spiromesifen. Efficacy evaluations indicated that spiromesifen was more effective than abamectin in controlling T. urticae on early season cotton at one-half rate of the lowest label rate. Results reported herein demonstrate that the multispectral optical sensor in lieu of manually counting T. urticae appears to be a promising tool for efficacy evaluations against acaricides for early season plants grown in greenhouses.

Remote Sensing Evaluation of Two-spotted Spider Mite Damage on Greenhouse Cotton.

The objective of this study was to evaluate a ground-based multispectral optical sensor as a remote sensing tool to assess foliar damage caused by the two-spotted spider mite (TSSM), Tetranychus urticae Koch, on greenhouse grown cotton. TSSM is a polyphagous pest which occurs on a variety of field and horticultural crops. It often becomes an early season pest of cotton in damaging proportions as opposed to being a late season innocuous pest in the mid-southern United States. Evaluation of acaricides is important for maintaining the efficacy of and preventing resistance to the currently available arsenal of chemicals and newly developed control agents. Enumeration of spider mites for efficacy evaluations is laborious and time consuming. Therefore, subjective visual damage rating is commonly used to assess density of spider mites. The NDVI (Normalized Difference Vegetation Index) is the most widely used statistic to describe the spectral reflectance characteristics of vegetation canopy to assess plant stress and health consequent to spider mite infestations. Results demonstrated that a multispectral optical sensor is an effective tool in distinguishing varying levels of infestation caused by T. urticae on early season cotton. This remote sensing technique may be used in lieu of a visual rating to evaluate insecticide treatments.

Mortality and reproductive effects of ingested spinosad on adult bollworms.

BACKGROUND: Upon emergence from their pupal cells, bollworm, Helicoverpa zea (Boddie), adults actively seek and feed on plant exudates before they disperse and reproduce on suitable host plants. This nocturnal behavior of the bollworm may be exploited as a pest management strategy for suppression of the insect by using an attractant/stimulant mixed with an insecticide to induce feeding to cause adult mortality or reproductive reduction/inhibition. This study aimed to determine in the laboratory whether or not spinosad when mixed with sucrose solution as a feeding stimulant and ingested by bollworm could influence mortality and reproduction of the insect. RESULTS: Sublethal concentrations of spinosad fed to laboratory-reared females confined with males significantly reduced percentage hatch of eggs at 0.1 mg L(-1), and it was reduced to near zero at 2.5 mg L(-1) when compared with females fed 2.5 M sucrose solutions only. The lethal concentration (LC(99)) for males captured from the field in sex-pheromone-baited traps was 73 mg L(-1) for 24 h response. Proboscis extension response was not inhibited significantly even at 10 g L(-1). In spite of a 137-fold increase in lethal dose concentration, spinosad did not inhibit feeding. CONCLUSION: A detailed study of laboratory-reared and field-collected bollworm adults relative to mortality and reproduction after ingestion of spinosad indicates that spinosad would be useful in an attract-and-kill strategy to control the insect when mixed with a feeding attractant/stimulant. Field validation of the data is warranted.

Aerial electrostatic-charged sprays for deposition and efficacy against sweet potato whitefly (Bemisia tabaci) on cotton.

BACKGROUND: The efficacy of aerial electrostatic-charged sprays was evaluated for spray deposit characteristics and season-long control of sweet potato whitefly (SWF), Bemisia tabaci Genn. biotype B (aka B. argentifolii Bellows & Perring), in an irrigated 24 ha cotton field. Treatments included electrostatic-charged sprays at full and half active ingredient (AI) label rate, uncharged sprays and conventional sprays applied with CP nozzles at full label rate with several different insecticides. RESULTS: Spray droplet size was significantly smaller for electrostatic-charged sprays than for conventional sprays in top- and mid-canopy locations. The seasonal mean numbers of viable eggs and live large nymphs on cotton treated with electrostatic-charged sprays were comparable with those on cotton treated with conventional applications. Lethal concentration (LC(50)) for adults for electrostatic-charged sprays was comparable with that for conventional sprays. CONCLUSION: The amenability of electrostatic-charged sprays to a wide array of pesticides with different chemistries should be a useful tool in combating insect resistance. Results reported here suggest that the potential exists for obtaining increased efficacy against whiteflies using an electrostatic spray charging system, and that additional research will be required to improve charge-to-mass (Q/M) ratio in order to increase deposition of pest control materials to the lower surfaces of cotton leaves where the whiteflies reside.