Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2002
Publication Date: 12/31/2002
Citation: PFENDER, W.F., ALDERMAN, S.C. EVALUATION OF POST-HARVEST BURNING OR FUNGICIDES TO REDUCE POLYETIC EPIDEMIC RATE IN ORCHARDGRASS CHOKE DISEASE. PLANT DISEASE. 2002. v.87. p. 375-379. Interpretive Summary: Orchardgrass is a high-quality forage grass used throughout the US for livestock. Choke disease, caused by a fungus, does not affect forage quality but can severely limit production of seed. The disease increases within a seed production field from year to year. Experiments were done to determine whether commonly-used systemic fungicides are effective in reducing spread of choke disease, and whether post-harvest burning of stubble has an effect. We found that the fungicides are ineffective in the field, even though they are toxic to the fungus in laboratory tests. Reclipping of stubble after harvest was also ineffective for disease management. Propane-assisted burning of post-harvest stubble did significantly decrease rate of disease spread in the stand, from 9.2% per year to 2.7% per year.
Technical Abstract: Epichloë typhina, causal agent of choke disease, is detrimental to orchardgrass seed production. The fungus grows systemically and persists indefinitely as an endophyte within the perennial host, and produces a stroma bearing conidia and ascospores about the time of host flowering. The spores are thought to infect plants through cut ends of tillers after swathing at harvest. Post-harvest treatments were evaluated for potential to interrupt the yearly spore-mediated infection cycle needed for plant-to-plant spread. Propiconazole and azoxystrobilurin fungicides reduced germination of conidia of E. typhina in vitro, but had no effect on stroma development or viability of conidia produced on infected plants. In field tests, fungicides applied to cut ends of post-harvest tillers were ineffective in reducing the rate of epidemic increase. Likewise, reclipping of stubble in an attempt to remove incipient infections in tillers did not reduce infection rates. However, propane-assisted burning of post-harvest stubble and vegetation did reduce polyetic epidemic rate to 2.7% per year, compared with approximately 9.2% per year in plots receiving the fungicide, reclip or check treatments. The results suggest the existence of infection courts in addition to the pith of reproductive tillers, and indicate that post-harvest burning may be useful in disease control.