Variation in Clarireedia spp. inhibition and turfgrass phytotoxicity among demethylation inhibitor fungicides
Open Access
- Author:
- Kahiu, Maureen
- Graduate Program:
- Agronomy
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- January 21, 2022
- Committee Members:
- Erin Connolly, Program Head/Chair
John Edward Kaminski, III, Thesis Advisor/Co-Advisor
Peter Landschoot, Committee Member
Wakar Uddin, Committee Member - Keywords:
- Demethylation inhibitor fungicides
phytotoxicity
DMIs
dollar spot - Abstract:
- Dollar spot is arguably the most common and economically important disease in turfgrass systems. Although several cultural practices can be implemented to reduce disease severity, fungicides are often required to meet acceptable standards for golf course turf. Among fungicides available for control of dollar spot, demethylation inhibitor fungicides (DMIs) are one of the most commonly used fungicide group to manage the disease. DMI fungicides have however been reported to cause phytotoxicity when applied in the summer. The objectives of this study were to 1) elucidate the phytotoxicity of commercially available DMIs when applied to annual bluegrass (Poa annua) (ABG) and creeping bentgrass (Agrostis stolonifera) (CBG) fairways; and 2) determine EC50, relative mean growth, and discriminatory dose values for nine commercially available DMIs for Clarireedia jacksonii isolates with varying levels of insensitivity. Fungicide treatments were applied to creeping bentgrass and annual bluegrass fairways for two consecutive years. Turfgrass injury caused by triticonazole was significant on annual bluegrass but not on creeping bentgrass. Repeated use of DMI fungicides has previously been reported to cause reduced sensitivity to Clarireedia spp. populations and injury to both ABG and CBG. Fifty isolates were screened across nine commercially available DMIs and discriminatory doses for each determined. Isolates of varying sensitivity levels to propiconazole were screened across determined discriminatory doses. In both experiments, mefentrifluconazole, myclobutanil, and triticonazole resulted in the least mycelial growth across sensitive isolates while prothioconazole and triadimefon resulted in the highest radial mycelial growth. On fungicide amended media, relative mean growth was lowest in the sensitive isolates followed by the moderately and highly insensitive isolates respectively.