Document Type

Thesis - Open Access

Award Date

2025

Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Adam Varenhorst

Abstract

Wheat, Triticum aestivum L., and sunflower, Helianthus annuus L., are major crops in South Dakota that are threatened by stem-boring insect pests capable of reducing yield and harvestability. In wheat, the wheat stem sawfly, Cephus cinctus Norton, has long been recognized as a destructive pest in the Northern Great Plains, yet its actual distribution within South Dakota remained uncertain. To determine its presence, a two-year survey was conducted across the state from 2023–2024, during which one to four wheat fields per county were sampled using standardized sweep net transects. Wheat stem sawflies were collected only from Harding and Perkins Counties in 2023 and from Harding County in 2024, contradicting earlier reports of broader infestations and indicating that growers outside these counties can continue cultivating hollow-stem wheat varieties without substantial risk from this pest. Next, the Dectes stem borer, Dectes texanus LeConte, a common stalk-boring pest of sunflower, poses an emerging concern primarily through preharvest stalk girdling that leads to lodging. With recent increases in infestations observed in biennial surveys and ongoing management adjustments to reduce red sunflower seed weevil damage via earlier planting, it is important to evaluate whether such planting shifts influence Dectes infestations in South Dakota. A two-year field experiment conducted at two locations in 2023 and 2024 compared early and late-planted sunflower and revealed consistently high levels of Dectes infestation across both planting dates, but greater lodging was observed in early-planted fields. Together, this research provides a comprehensive assessment of two key stem-boring insects in South Dakota, confirming the highly localized presence of wheat stem sawfly and clarifying the interaction between sunflower planting date and Dectes stem borer infestations.

Publisher

South Dakota State University

Download

Share

COinS
 

Rights Statement

In Copyright