Date of Award
Master of Science
Plant Pathology and Microbiology
Mark L. Gleason
Organic production of cucurbit crops in the Midwest is limited by several insect pests (e.g., striped cucumber beetle, spotted cucumber beetle, squash bug, squash vine borer) and the bacterial diseases they vector (e.g., cucurbit bacterial wilt and cucurbit yellow vine disease (CYVD)). Current management strategies – low tunnels and insecticides – fail to provide reliable protection, are not durable, and are harmful to beneficial insects such as pollinators. Organic producers in the Midwest need more effective pest management options to consistently produce cucurbit crops.
A 3-year field experiment aimed to develop new row cover strategies for full-season, organic control of cucurbit insect and disease pests. The objectives were to evaluate traditional and modified row cover strategies for differences in incidence of disease and insect pest damage, number of insecticide applications, number and weight of marketable fruit, and maximum temperatures inside tunnels. Full-season “mesotunnels” – nylon-mesh fabric supported by 3.5-foot-high conduit hoops - resulted in the lowest incidence of disease and insect pest damage in muskmelon and acorn squash, and no disease or insect pest damage in muskmelon. Full-season mesotunnels required no insecticide applications, whereas a noncovered control treatment required the most insecticide applications and part-season mesotunnels and low tunnels were intermediate. The weight of marketable muskmelon in full-season mesotunnels was higher than in the noncovered control for all 3 years and higher than in the low tunnels and part-season mesotunnels for 1 of 3 years. The weight of marketable muskmelon in part-season mesotunnels was higher than in the non-covered control in 2 years. The number of marketable muskmelon in full-season mesotunnels was higher than in the noncovered control in 2 years and higher than in low tunnels in 1 year. The number of marketable muskmelon in part-season mesotunnels was higher than in the non-covered control in 1 year. The weight of marketable squash in full-season mesotunnels was higher than in low tunnels for all 3 years, higher than in low tunnels and part-season mesotunnels in 1 year. The weight of marketable squash in part-season mesotunnels was higher than in the non-covered control in 1 year. The number of marketable squash in full-season mesotunnels was higher than in the non-covered control in all 3 years and higher than in low tunnels and part-season mesotunnels in 1 year. The number of marketable squash in part-season mesotunnels was higher than in the non-covered control in 1 year. The nylon-mesh row cover material used for mesotunnels provided plant coverage throughout the growing season with minimal increase in midday air temperature inside the tunnels, whereas the spunbond polypropylene row cover fabric used in low tunnels raised maximum midday temperatures to levels that could damage plants.
A second 3-year field experiment investigated weed management strategies for mesotunnels. The objective was to evaluate between-row mulching strategies for differences in weed suppression, number and weight of marketable fruit, and contribution to soil permanganate oxidizable carbon (POXC) in muskmelon and acorn squash production in mesotunnels. Chopped corn stover provided more effective weed suppression on both crops in 2018 than a living mulch consisting of annual ryegrass and red clover, and more effective weed suppression than a bare-ground control treatment in 2016 on both crops. Living mulch never outperformed corn stover in suppressing weeds, but did outperform the bare-ground treatment in 2016 on muskmelon and in 2017 on acorn squash. POXC levels were higher for soil in the corn stover treatment than in the living mulch treatment in 2016 in muskmelon. In the same year, corn stover increased POXC compared to bare ground in acorn squash. Corn stover resulted in higher number and weight of marketable muskmelon than living mulch in 2017 and a higher number of marketable muskmelon than bare ground in 2016. In acorn squash, living mulch resulted in higher number of marketable fruit than bare ground in 2017.
These field experiments addressed major limitations to production of organic cucurbit crops in the Midwest, particularly lack of effective pest, disease, and weed control strategies. My experiments were the first replicated trials to examine the use of mesotunnels for cucurbit production in the Midwest, and provide organic cucurbit growers with new options for pest, disease, and weed management.
The final objective of my thesis was to develop a teaching case study to enhance undergraduate science education. The case study highlighted differences in disease management between organic and conventional production methods in the context of commercial cucurbit-crop production, and challenged students to come up with a reasonable management plan for a fictional muskmelon producer in Iowa. The case was tested in an undergraduate plant pathology course at Iowa State University, and modified according to student feedback prior to submission for peer review to the open-access online journal The Plant Health Instructor.
Nelson, Hayley, "Disease and insect pest management in organic cucurbit production" (2019). Graduate Theses and Dissertations. 17066.