Doctoral Dissertations

Date of Award

12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plants, Soils, and Insects

Major Professor

Brandon J. Horvath

Committee Members

Alvin R. Womac, Bonnie H. Ownley, John C. Sorochan, Alan S. Windham

Abstract

Large patch (Rhizoctonia solani AG 2-2LP) epidemics cause significant damage to Japanese lawngrass (JLG; Zoysia japonica) in the transition zone. Large patch primarily affects the stems and sheaths of JLG and is difficult to control using traditional fungicide sprays. Field and growth chamber experiments were conducted during 2015-2016 in TN and GA to evaluate methods to enhance fungicidal control of large patch in JLG landscapes. The 1st experiment evaluated the most critical application target site that resulted in the greatest amount large patch control. In this experiment, four fungicides (azoxystrobin, flutolanil, tebuconazole, and chlorothalonil) were dispensed as single droplets on either the stem, sheath, or leaf plant part of JLG. Plants were evaluated for large patch control and photochemical efficiency (Fv/Fm). The 2nd experiment evaluated the effects of spray rate volume ((93, 374, 748, and 1496 L ha-1) and adjuvants on large patch control and spray deposition quality on JLG. Results of the 1st experiment suggested that JLG treated with fungicides dispensed on the stem or sheath exhibited significantly lower large patch severity and higher Fv/Fm values compared to JLG receiving leaf applications on most rating dates. Results of the 2nd experiment suggested that increasing the spray rate volume from 93 to 1496 L ha-1 improved large patch control by more than 20% depending on the fungicide. On most rating dates, each increase in spray rate volume resulted in significant decreases in large patch severity. The addition of adjuvants in the spray solution had less pronounced impacts compared to spray rate volume. Increases in spray rate volume were also critical in depositing more spray solution on the stems and sheaths of JLG plants. Higher spray rate volumes increased the percentage of stems and sheaths that contained spray deposits by as much as 35% compared to the lowest spray rate volume. This research demonstrated that higher spray rate volumes were able to penetrate the spray solution lower in the canopy near the site of pathogen infection. Increased spray rate volume applications were identified to enable increased fungicide deposition lower in the canopy and results in enhanced fungicidal control of large patch.

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