Date of Award:

8-2024

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Fabiane Mundim

Committee

Fabiane Mundim

Committee

Ricardo A. Ramirez

Committee

Earl Creech

Committee

Corey Ransom

Committee

Robert Scheffer

Abstract

With climate change, it is predicted that more frequent high temperatures and drought severity will lead to an increase in damage caused by pests that thrive under these conditions. Spider mite outbreaks, for example, are associated with plant waterstress and there is evidence that some weeds are more resilient and adapted to drought than some crops, leading to major concerns for the management of these two pest types. Weeds directly compete with crops for limited resources, but what is unclear is which weeds harbor spider mites and whether they exacerbate the impact of spider mites on corn crops under water-stressed environments like Utah. In addition, farmers have access to technologies including drought tolerant corn hybrids in the region to help alleviate water-stress but their impact on crop-pest interactions and management is unknown. Therefore, I started by evaluating the competitive effects of redroot pigweed (Amaranthus retroflexus) and common lambsquarters (Chenopodium album) on drought tolerant (DT) and drought susceptible (DS) corn hybrids, exposed to optimal and reduced irrigation levels in a semi-controlled and greenhouse studies. Weeds accumulated high shoot biomass when growing with DS corn than DT corn under reduced irrigation suggesting that DT corn outcompeted weeds under water stressed conditions. I then evaluated the critical period of weed control (CPWC) in a DT versus DS stand of corn, exposed to the two irrigation levels. DT corn had a shorter CPWC compared to DS, emphasizing the role of DT in outcompeting weeds, thus the shorter period of weed control. Finally, I conducted a survey to identify weed species at the edges of corn fields to evaluate associated spider mite species. This was followed by a parallel field study to investigate how varied irrigation levels impact spider mite infestations from weeds to corn. I identified weeds acting as hosts to spider mites at the edges of corn fields and observed that reducing irrigation level led to an increase in mite populations and their eggs. Mite and egg densities were also lower on DT corn compared to DS corn. Results show the potential of DT corn in outcompeting weeds and spider mite populations under water stressed conditions. This information may assist in developing strategies for managing the two pest types, consequently, contributing to the development of integrated pest management for corn production systems in water stressed environments.

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