Evaluation of Postharvest Burning and Fungicides to Reduce the Polyetic Rate of Increase of Choke Disease in Orchardgrass Seed Production.

Epichloë typhina, causal agent of choke disease, is detrimental to orchardgrass seed production. The fungus grows systemically, persists indefinitely as an endophyte within the perennial host, and produces a stroma bearing conidia and ascospores at the time of host flowering. The ascospores or conidia are thought to infect plants through the cut ends of tillers after swathing at harvest. The objective of this study was to evaluate the potential of systemic fungicides and postharvest treatments (burning and reclipping) to reduce the rate of increase of choke disease among plants. The fungicides propiconazole and azoxystrobin reduced germination of conidia of E. typhina in vitro, but had no effect on development of stroma or viability of conidia produced on infected plants. In field tests, fungicides applied to the cut ends of tillers after harvest were ineffective at reducing the rate of increase in disease. Likewise, reclipping of orchardgrass stubble after harvest, in an attempt to remove incipient infections in the tillers, did not reduce the rate of disease increase in the stand. However, propane-assisted burning of postharvest stubble did reduce the polyetic epidemic rate to 2.7% per year, compared with approximately 9.2% per year in plots receiving the fungicide, reclipping, or control treatments. The results suggest that postharvest burning may be useful in controlling choke disease and raise the possibility that there are infection courts other than the pith of cut reproductive tillers.