Rice Disease Research and Management, 2013


Project Leader

Christopher Greer, rice farming systems advisor, UC Cooperative Extension Sutter, Yuba, Placer and Sacramento counties

The overall objective of this research is to increase understanding of the biology of California rice diseases and to develop effective, economically viable management practices for these diseases. Specific objectives for 2013 research included:

   • Evaluate timing and potential of fungicide applications for aggregate sheath spot, stem rot, and rice blast.

   • Compare genetic relatedness of blast isolates in relation to a newly identified race of the fungus that is pathogenic to rice variety M-208.

Fungicide evaluations

For a second year, research focused on evaluation of fungicide product efficacy against stem rot, aggregate sheath spot, and rice blast.

Three small-plot fungicide trials were established in M-206 commercial rice fields to evaluate the standard fungicide Quadris® alongside the more recently introduced product Quilt Xcel™. Application timing specifically targeted aggregate sheath spot and rice blast diseases during panicle emergence.

In general, 2013 was an early planting season and an average year for rice diseases. Both aggregate sheath spot and stem rot incidence and severity appeared to be greater than in 2012. Disease levels in 2013 were excellent for evaluating rice disease control materials.

Across locations both products significantly reduced stem rot and aggregate sheath spot incidence and severity. Aggregate sheath spot incidence was reduced 69% to 77%, while stem rot incidence was reduced 31% to 40%. Head-rice milling quality and harvest grain moisture were significantly higher in plots treated with Quadris® and Quilt Xcel™. Harvest grain moisture was 1% to 1.5% higher and head-rice milling quality was 3.5% to 4.5% higher in fungicide-treated plots. All fungicide treatments, except for a late timing of Quadris®, significantly increased yields over control plots by 200 to 360 pounds/acre.

The long-term goal of this work is to develop an integrated rice-disease management program for California growers based on sound fungicide data and pathogen biology. Future research will focus on evaluating Quadris®, Quilt Xcel™, and Stratego® fungicides for disease management in California rice. Management of both aggregate sheath spot and stem rot diseases will be priorities. Earlier fungicide timings will include a propanil application timing that may boost impact on stem rot.

Blast isolates

M-208 is the only commercially available rice variety in California with specific resistance to the IG-1 race of the blast pathogen. IG-1 was the only race of this pathogen known to exist in California until recently. Confirmed cases of limited blast infestations in M-208 fields, however, indicate that a new race of the pathogen has evolved through mutation or has been introduced into California. M-208 is still resistant to IG-1 but not to the new race.

Previously collected blast isolates from 2011 and 2012 will undergo genetic analysis in 2014. The goal is to identify genetic tools that will provide a better understanding of the loss of resistance in M-208 and to provide a solid base for future studies of the blast organism.