Date of Graduation

5-2019

Document Type

Thesis

Degree Name

Master of Science in Plant Pathology (MS)

Degree Level

Graduate

Department

Plant Pathology

Advisor/Mentor

Ken Korth

Committee Member

Terry Spurlock

Second Committee Member

Nick Seiter

Third Committee Member

Travis Faske

Keywords

Canopy Density, Corn, Disease identification, Distribution, Foliar disease, Microclimates, Normalized Difference Vegetative Index, Precision Agriculture, Predictive scouting models, Soil phosphorus maps, Southern rust, sub-field environmental conditions

Abstract

Southern rust caused by the fungus Puccinia polysora (Underwood) is the most economically important foliar disease in corn (Zea mays) (Linnaeus) (Cyperales: Poaceae)) for Arkansas. The objective of this work was to determine distribution of southern rust in corn and to determine factors that may control its distribution.

During the 2017 and 2018 season, seven corn fields in Arkansas were rated for southern rust. After disease confirmation, fields were marked with GPS sample point locations in a grid pattern across the entire field. Ratings for disease severity were taken below, at, and above the ear leaf at each point every two weeks until maturity. Data analyses showed that southern rust did not occur randomly, which is common thought about foliar diseases. However, the disease spread in a uniform fashion across each field but also built in localized areas and were statistically clustered (P = 0.05). This distribution indicates the disease is likely dependent on clustered environmental phenomenon’s that favor development. Soil samples were collected at each GPS point. A significant positive correlation existed between relative levels of phosphorus and southern rust severity in five of seven fields (P = 0.05). A normalized difference vegetative index (NDVI) ratio was calculated for four fields. There was a significant positive correlation with relatively higher canopy density in early June and relatively higher southern rust severity weeks later (P = 0.05).

A planting date study was conducted over the 2017 and 2018 growing seasons. The trial was conducted in randomized 4-row wide plots in 2017 and 2-row wide strips in 2018 with six planting dates (15 May, 1 Jun, 15 Jun, 1 Jul, 15 Jul, 1 Aug). Objectives included if southern rust severity influenced pre-harvest lodging, and disease severity relative to date and growth stage. Lodging was not observed in either year and southern rust was most severe in early planted plots compared to later planted plots. In both years, southern rust infested the three earliest planting dates 2-3 weeks prior to the later three planting dates. These results suggest that southern rust severity is dependent on another factor in the field, likely environmental.

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