Spray deposit patterns and persistence of diflubenzuron in some terrestrial components of a forest ecosystem after application at three volume rates under field and laboratory conditions

Abstract

Spray deposit patterns and persistence of diflubenzuron [1‐(4‐chlorophenyl)‐ 3‐(2,6‐difluorobenzoyl)urea] in white pine (Pinus strobus L.) and sugar maple (Acer saccharum Marsh.) canopies, forest litter and soil were studied after aerial application of a 250 g kg−1 wettable powder formulation, ‘Dimilin® WP‐25’, at 70 g active ingredient (a.i.) ha−1, using three volume rates (10, 5 and 2.5 liters ha−1) over three blocks in a mixed forest near Kaladar, Ontario, Canada, during 1986. Spray droplets were sampled at ground level using ‘Kromekote®’ cards, and diflubenzuron deposits were collected on glass plates. Droplets were the largest (with a volume median diameter of 250 μm) at the 10 liters ha−1 rate, resulting in the highest number of droplets per cm2 on the Kromekote cards and deposits of diflubenzuron on glass plates. Deposits on foliage, litter and soil were also correspondingly the highest. At the 5.0 and 2.5 liters ha−1 rates, volume median diameter values were smaller (195 and 150 μm, respectively) and deposits on the substrates were markedly lower. In the spray block that received 10 liters ha−1, diflubenzuron persisted in foliage as long as 120 days after treatment, but it lasted for only about a week in forest litter and soil samples. At 5 and 2.5 liters ha−1, diflubenzuron failed to persist in foliage as long, and residues in litter and soil, which were barely above the quantification limit, persisted only for a few days. Laboratory studies, conducted under constant meteorological conditions using different droplet‐size spectra, showed that deposit levels were not affected when the volume median diameter of the spray cloud decreased from 253 μm to 145 μm, but were markedly reduced as this progressively decreased from 92 to 37μm. The dissimilarities between the field and laboratory findings were attributed to meteorological and other factors influencing droplet deposition on tree canopy in aerial applications of pesticides over forests.

Persistence and mobility of tebufenozide in forest litter and soil ecosystems under field and laboratory conditions

“…13 The residual concentrations (individual values measured) obtained during the initial 85 days after spray were subjected to regression analysis, and were found to Ðt into eqns (1) to (3) :…”

Deposition, distribution, persistence and fate of bacillus thuringiensis variety kurstaki (BTK) in pecan orchards following aerial and ground appucations to control pecan nut casebearer larvae

“…These factors include spray droplet size (Yates and Akesson, 1973;, release height (Teske and Barry, 1993), aircraft speed, prevailing meteorological conditions [especially wind speed and direction, and relative humidity (RH), if the formulation is aqueous] (Picot et al, 1993), formulation properties (Sundaram et al, 1997a), volume and dosage rates (Sundaram, 1991), nozzle type and mode of application (rotary vs fixed wing aircraft) (Sundaram et al, 1997b), etc. Quantification of on-target deposits is essential to understand the efficiency of the spray operation, and to relate it to the observed efficacy.…”

“…The coverage [i.e., droplet density (droplets/cm 2 )] and droplet size spectra of dyed spray-mixes have been assessed routinely in the past using Kromekote® cards (K-cards) and other collection surfaces (Sundaram, 1991). Direct quantification of the AI on the target and simulated matrices (Sundaram et al, 1994a), although labour intensive and expensive, is the preferable method to minimize potential extrapolative errors in order to evaluate, accurately, the deposition and dissipation characteristics (Duan et al, 1994).…”

A simple empirical model to predict forest insecticide ground-level deposition from a compendium of field data

“…Most of the deposit data summarized here are taken from studies to assess efficacy or environmental fate and effects of forest insecticides, and variables to explain spray application and deposit dynamics were not measured. Others have studied the influences of variables like atmospheric stability, [10] formulation additives, [11] formulation properties, [12] application rates, [13] atomization properties, [14] meteorological conditions, [15] aircraft turbulence, [16] and droplet size spectra [17] on spray dispersal and deposit.…”