Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2015
Publication Date: 4/12/2015
Citation: Martin, D.E., Latheef, M.A., Lopez, J. 2015. Evaluation of selected acaricides against two-spotted spider mite (Acari: Tetranychidae) on greenhouse cotton using multispectral data. Experimental and Applied Acarology. 66(2):227-245.
Interpretive Summary: Greenhouse studies were conducted on the effect of partial chemical rates using two different active ingredients to control two-spotted spider mites on cotton. A handheld multispectral optical sensor was effectively used to quantify spider mite damage to the cotton. It was determined from the study that a half-rate of each chemical was just as effective at controlling spider mites as the lowest labelled rate. Chemical companies, farmers, crop consultants and applicators will be able to use the results of this study to better monitor cotton health and reduce chemical usage and environmental loading while maintaining good control of these cotton pests.
Technical Abstract: Two-spotted spider mite (TSSM), Tetranychus urticae (Koch), is an early season pest of cotton in the mid-southern United States 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 kmh, a 650033 nozzle delivered a spray volume of 18.7 L/ha. The active ingredient rates were ', ¼, ½ and the lowest label recommended rates. 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 (NDVI) which described numerically 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. Efficacy evaluations indicate that both abamectin and spiromesifen at the ½ active ingredient rates, respectively, improved plant health and suppression of T. urticae on cotton significantly compared to control at 12 and 14 days post-treatment. The volume median diameter (Dv0.5) of spray droplets was 217.6 and 258.3 µm, respectively, for abamectin and spiromesifen at the ½ rate. This study demonstrated that a multispectral optical sensor can be an effective sampling tool for the quantitative assessment of TSSM damage on cotton in greenhouse and field plot tests. We posit that field studies are required to validate the results reported herein.