Application Pressure and Carrier Volume Affects the Concentration of Azoxystrobin on Peanut Foliage and in Soil

Abstract

ABSTRACT Azoxystrobin can be used to manage pod rot of peanuts, and applications are typically made at mid-season or later, when it can be difficult to move the fungicide through the foliage and down into the soil. Spanish peanuts were sprayed with azoxystrobin in 2013 at carrier volumes ranging from 252 to 1038 L ha−1 and pressure ranging from 138 to 552 kPa; and in 2014 virginia peanuts were sprayed with carrier volumes ranging from 131 to 524 L ha−1 and pressure ranging from 138 to 414 kPa. Square root transformed azoxystrobin concentration (√A in ppm) on foliage at carrier volumes < 300 L ha−1 was higher in 2 of 3 experiments (√A averaged 2.4 times higher) with spanish peanuts and 1 of 2 experiments (√A averaged 1.3 times higher) on virginia peanuts, than at volumes ≥ 524 L ha−1. A linear model could be used to describe the negative relationship between carrier volume and (√A) on foliage for all three applications on spanish peanuts. Azoxystrobin concentrations in soil were 3 times higher for carrier volumes < 300 L ha−1 in 2 of 3 experiments on spanish peanuts and were not affected by carrier volume on virginia peanuts, than carrier volumes ≥ 524 L ha−1. However, application pressure of 138 kPa resulted in higher concentrations of azoxystrobin (1.7 times higher) in the soil in 1 of 2 trials than using an application pressure of 515 kPa on virginia peanuts. Foliar concentrations of azoxystrobin on virginia peanuts declined over time and irrigation events. However, soil concentrations of azoxystrobin generally increased between 0 and the first irrigation event for the higher carrier volume (524 L ha−1), but did not change between the first and second irrigation event. Attempts to force azoxystrobin through the peanut canopy with high pressure (414 to 552 kPa), high carrier volume (≥524 L ha−1) or combinations of high pressure and high carrier volumes were unsuccessful at increasing azoxystrobin concentrations in soil compared to more traditional carrier volume and pressure.