Agronomy and Horticulture, Department of


First Advisor

Loren J. Giesler

Date of this Version


Document Type



Arneson, N.J. 2019. Effect of soil-applied protoporphyrinogen oxidase inhibitor herbicides on soybean seedling disease. Masters Thesis. University of Nebraska-Lincoln, Lincoln, NE.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor Loren J. Giesler. Lincoln, Nebraska: May, 2019.

Copyright (c) 2019 Nicholas J. Arneson


Seedling disease is one the most economically important diseases of soybean in the United States. It is commonly caused by Fusarium spp., Rhizoctonia solani, Pythium spp., and Phytophthora sojae, alone, or together as a disease complex. Fungicide seed treatments continue to provide the most consistent management of seedling diseases. Soil-applied protoporphyrinogen oxidase (PPO) inhibitor herbicides are used preemergence in soybean production to manage several broadleaf weeds. Applications of PPO-inhibitors can result in phytotoxic injury to soybean when environmental conditions are not favorable for soybean growth. These environmental conditions can favor seedling disease development as well. In this thesis, two studies were conducted to determine the effect of soil-applied PPO-inhibitors on soybean seedling disease development in Nebraska under field and controlled conditions.

The first study assessed the effect of two PPO-inhibitors and a fungicide seed treatment on seedling disease and yield in 9 soybean fields in Nebraska. PPO-inhibitor injury occurred at 7 of 9 locations with inconsistent effects on seedling disease, where increases in root rot severity of 6.6–28.1% were observed at 5 of 9 locations, decreases of 4.7–10.9% at two locations, and no effect at three locations. None of these effects impacted yield at any of the locations. Fungicide seed treatment did not reduce root rot severity at any location; however, it increased yield at two locations.

The second study investigated the effect of PPO-inhibitors on seedling disease caused by Fusarium solani under controlled conditions. Disease pressure was consistent throughout this study, with root rot severities ranging 32.1–38.9%. PPO-inhibitor injury occurred in all experiments with severities ranging 7.0–33.0%. Sulfentrazone alone increased root rot severity 9–12%.

There was an effect of PPO-inhibitors on seedling disease development, although results were inconsistent, indicating a need for further research. PPO-inhibitors should continue to be used in part of an integrated weed management program and fungicide seed treatments should be used in fields that have a history of seedling disease.

Advisor: Loren J. Giesler