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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of ground and aerial application, fungicide deposition and biological activity in large pecan tree canopies.

Authors
item Reilly, Charles
item Wood, Bruce
item Cottrell, Ted

Submitted to: Southeastern Pecan Growers Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 15, 2007
Publication Date: July 7, 2007
Citation: Reilly, C.C., Wood, B.W., Cottrell, T.E. 2007. Comparison of ground and aerial application, fungicide deposition and biological activity in large pecan tree canopies. Southeastern Pecan Growers Meeting Proceedings. 100:115-123.

Interpretive Summary: Estimates of the vertical spray deposition of fungicides in pecan canopies of large trees were conducted to determine if the entire canopy was protected from fungal pathogens. Metallic tracer application by air blast sprayer at three spray volumes (50, 100 and 200 gallons/acre) or three ground speeds (1.5, 2.0 and 2.5 mph) plus aerial application (8 gallons/acre) were used to deliver tracers to canopies. Deposition of metallic tracers nickel and tin on foliage, at molar amounts equivalent to the molar rate of active ingredient in Orbit and SuperTin, applied at 50, 100 or 200 gallons per acre and 2.0 mph was numerically similar at each of the five heights (5, 25, 50, 75 and 100% of canopy height). For each volume (50, 100 and 200), deposition was greatest at lower parts of the canopy and decreased upward through the canopy. Inhibition of the fungal pathogens on agar was 80% or greater at 5 ppm for most fungi, however, deposition of tracers applied using an air-blast sprayer were less than 5 ppm at the two highest sampling sites (75 and 100% of the canopy height), thus the upper 25% of the canopy apparently does not receive high enough rate of fungicide to prevent disease development.

Technical Abstract: The study was conducted to determine vertical spray deposition in pecan canopies of large trees and to estimate the biological activity of the deposited fungicides. Tracer elements were used at molar concentrations equivalent to the molar amount of active ingredient found in the recommended rates of certain fungicides. Metallic tracer application by air blast sprayer at three spray volumes (50, 100 and 200 gallons/acre) or three ground speeds (1.5, 2.0 and 2.5 mph) plus aerial application (8 gallons/acre) were used to deliver tracers to canopies. Recovery of metallic tracer from pecan foliage and subsequent quantification of the amount recovered enabled calculation of an equivalent molar amount of fungicide active ingredient being deposited to pecan foliage at different heights in the tree as a function of spraying parameters. Deposition of metallic tracers Ni and Sn) on foliage, at molar amounts equivalent to the recommended molar rate of active ingredient in Orbit and SuperTin, applied at 50, 100 or 200 gallons per acre and 2.0 mph was numerically similar at each of the five heights (5, 25, 50, 75 and 100% of canopy height). For each volume (50, 100 and 200), deposition was greatest at lower parts of the canopy and decreased upward through the canopy. Inhibition of the fungal pathogens on agar was 80% or greater at 5 ppm for most fungi, however, deposition of tracers applied using an air-blast sprayer were less than 5 ppm at the two highest sampling sites (75 and 100% of the canopy height), thus the upper 25% of the canopy apparently does not receive high enough rate of fungicide to prevent disease development.

Last Modified: 7/31/2014
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